Journal of Analytical Toxicology,Vol. 28, April 2004
Urinary Pharmacokinetics of 11-Nor-9-carboxy-A 9tetrahydrocannabinol after Controlled Oral Ag.
letrahydrocannabinol Administration
Richard A. Gustafson 1, Insook Kim 1, Peter R. Stout 2, Kevin L. Klette 3, M.P. George 4, Eric T. Moolchan 1,
Barry Levines, and Marilyn A. Huestis 1,*
IChemistry and Drug Metabolism, Intramural ResearchProgram, National Institute on Drug Abuse, National Institutes of Health,
5500 Nathan Shock Drive, Baltimore, Maryland 21224; 2AegisSciencesCorp., 345 Hill Avenue, Nashville, Tennessee37210;
3Navy Drug Screening Laboratory, P.O. Box 113, Bldg. H-2033, Naval Air Station, Jacksonville, Florida 32212;
4Quest Diagnostics, Inc., 506 EastState Parkway, Schaumburg, Illinois 60173; and SUniversityof Maryland,
Department of Epidemiology and Preventive Medicine, Baltimore, Maryland 21201
]Abstract
Understanding the pharmacokinetics of orally administered
cannabinoids is vitally important for optimizing therapeutic usage
and to determine the impact of positive tests on drug detection
programs. In this study, gas chromatography-mass spectrometry
(limit of quantitation = 2.5 ng/mL) was used to monitor the
excretion of total 11-nor-9-carboxy-A%tetrahydrocannabinol
(THCCOOH) in 4381 urine voids collected from seven participants
throughout a controlled clinical study of multiple oral doses of
THC. The National Institute on Drug Abuse Institutional Review
Board approved the study and each participant provided informed
consent. Seven participants received 0, 0.39, 0.47, 7.5, and 14.8
mg THC/day for five days in this double blind, placebo-controlled,
randomized protocol conducted on a closed research ward. No
significant differences (P_<0.05) were observed in mean time of
maximum excretion rate, mean maximum excretion rate, and
mean terminal elimination half-life (t,/2) between the four THC
doses, with ranges of 67.4 to 94.9 h, 0.9 to 16.3 pg/h, and 44.2 to
64.0 h, respectively. Mean apparent elimination t,/2 of 24.1 • 7.8
and 21.1 • 4.3 h for the 7.5 and 14.8 rag/day doses, respectively,
were calculated from the excretion rate curve prior to the last
urine sample with a THCCOOH concentration _>15 ng/mL. An
average of only 2.9 • 1.6%, 2.5 • 2.7%, 1.5 • 1.4%, and 0.6 •
0.5% of the THC in the 0.39, 0.47, 7.5, and 14.8 rag/day doses,
respectively, was excreted as THCCOOH in the urine over each
14-day dosing session. This study demonstrated that the terminal
urinary elimination tl a of THCCOOH following oral administration
was approximately two to three days for doses ranging from 0.39
to 14.8 mg/d. These data also demonstrate that the apparent
urinary elimination t,/2 of THCCOOH prior to reaching a 15 ng/mL
concentration is significantly shorter than the terminal urinary
elimination t,/2. These controlled drug administration data should
* Author to whom correspondenceshould be addressed. Marilyn A. Huestis, Ph.D.,
Acting Chief, CDM, IRP, NIDA, NIH, 5500 Nathan Shock Dr., Baltimore, MD 21224.
E-mail: mhuestis@intra,nida,nih.gov.
160
assist in the interpretation of urine cannabinoid results and provide
clinicians with valuable information for future pharmacological
studies.
Introduction
There are important reasons to understand the pharmacokinetics of oral Ag-tetrahydrocannabinol (THC), the principle psychoactive constituent of Cannabis. A major initiative
in pharmacological research is the development of cannabinoid
therapeutic agents. In 1999, the United States National
Academy of Sciences, Institute of Medicine called for clinical
trials to test the effectiveness of cannabinoids in pain relief,
control of nausea and vomiting, appetite stimulation, and other
indications and of improved delivery systems (1). Studies on
the administration of THC and other cannabinoids via oral, inhalation, and sublingual routes are being conducted. Currently, there are two oral medications containing synthetic
THC, dronabinol (Marinol~ and nabilone (Cesamet~ however, only dronabinol is approved for use in the United States.
Both drugs may be prescribed as antiemetics for chemotherapy-related nausea and vomiting and as appetite stimulants
for anorexia/cachexia syndrome associated with AIDS.
The last decade has seen an expanding global market for
food products and nutritional supplements derived from or
containing cannabis material. One such item is hemp oil,
which may contain a variable amount of THC (2,3). Hemp oil
is reported to contain a favorable ratio of essential fatty acids,
o~-linolenicacid and linoleic acid, which purportedly provide
health benefits. Ingestion of these products may result in positive urine drug tests (4,5). This has led to questions about the
validity of urine drug tests intended to deter drug use in treat-
Reproduction(photocopying)of editorialcontentof thisjournalis prohibitedwithoutpublisher'spermission.
Journal of Analytical Toxicology, Vol. 28, April 2004
ment, workplace,criminal justice, and military programs.
THC is rapidly oxidized to 11-hydroxy-A9-tetrahydrocannabinol (11-OH-THC), an equipotent psychoactive metabolite,
and further to the non-psychoactive 11-nor-9-carboxy-A9tetrahydrocannabinol (THCCOOH).Smaller quantities of other
metabolites are produced by minor metabolic pathways (6).
Cytochrome P450enzymes, CYP3A4, CYP2C9, and CYP2C11
are responsible for the oxidative activity, primarily in the liver
but to a lesser extent in other tissues (7). These metabolites
generally undergo further biotransformation to glucuronide
conjugates, with THCCOOH glucuronic acid as the primary
urinary metabolite of THC.
Several studies reported that ingestion of hemp oil can produce positive urine tests for cannabinoids (2,8-10). Lehmann
et al. (2) found THC concentrations of 3 to 1500 IJg/g in 25
hemp oil samples. Six subjects ingested one or two tablespoons
of 1500 IJg/g hemp oil (approximately 16.5 and 33 mg THC).
Positive urine specimens were observed for up to six days with
a 50 ng/mL cannabinoid imrnunoassay cutoff and a 15 ng/mL
THCCOOH gas chromatography/mass spectrometry (GC-MS)
cutoff. Costantino et al. (10) reported that seven subjects ingesting 15 mL of hemp oil of an unknown THC concentration
had positive urine drug tests by immunoassay at a cutoff of 20
ng/L for up to 48 h after ingestion. GC-MS analysis of urine
specimens for THCCOOH identified concentrations up to 78.6
ng/L. This is substantially above the federally mandated urine
THCCOOH confirmation cutoff concentration of 15 ng/L.
In the past fewyears, there has been a reduction in the THC
concentration of hemp food products (11). The decrease is due
to improved quality control measures such as more thorough
seed cleaning. The Drug Enforcement Agencyand Justice Department added an interpretive rule to 21 CFR Part 1308 in the
Federal Register in October 2001 (12). This addition to the
Controlled Substances Act declared that any product containing any THC is a Schedule I controlled substance. However,
hemp oils with considerable THC concentration are available
in other countries, over the Intemet, and from older, previously
purchased oils. Therefore, hemp oil ingestion may be used by
some to justify a positive cannabinoid urine test and to conceal
illicit cannabis use.
Early studies on THC metabolism following intravenous,
oral, or smoked administration generally entailed a singledose administration followed by a relatively short monitoring
period (13-15). Estimates of drug disposition and elimination
half-lives in blood, urine, and feces were determined through
administration of radiolabeled THC, a very sensitive technique
(14,16,17). One drawback to the studies with radiolabeled THC
is low selectivity, the inability to differentiate THC from its
metabolites. Also, shorter estimates of elimination half-life
were observed because of a lack of sensitive analytical techniques to monitor the excretion of cannabinoid metabolites for
extended periods of time (18).
In addition, it has been logistically impractical to collect
and analyze large numbers of urine specimens required for a
detailed excretion study until the development of large-scale
urine drug testing laboratories. In 1998, Huestis et al. (18)
reported on the urinary excretion half-life of THCCOOH following the smoking of marijuana cigarettes. All urine voids
were collected and individually analyzed by GC-MS with a 0.5
ng/mL limit of quantitation. Applying the amount remaining
to be excreted method, they reported THCCOOHmean urinary
terminal elimination half-livesof 31.5 • 1.0 and 28.6 • 1.5 h for
the 1.75% and 3.55% THC cigarettes, respectively,with a seven
day monitoring period.
Although there are several pharmacokinetic studies of THC
and its metabolites in plasma or urine after smoked cannabis
(18-23), few studies have addressed the urinary pharmacokinetics of THCCOOHfollowingoral THC administration (15,17).
Law et al. (15) studied the urinary kinetics of THC and combined metabolites following a single oral 20-rag dose of THC.
Urinary cannabinoid concentrations were adjusted with the
creatinine concentration for variations in urine flow rate. They
reported a urinary cannabinoid half-life of 25 • i h based on
single daily urine samples for 14 days. In 1990, Johansson et al.
(17) orally administered 20 mg of [14C]THC to two naive users
and monitored urinary excretion for 120 h. THCCOOH quantitation was determined by a GC-MS method with a 7 ng/mL
limit of detection. A THCCOOH urinary half-life of 14.5 h was
found for urine samples taken between 24 and 48 h, and a
17.7 h half-life for the 48-72-h monitoring period.
The objective of this study was to investigate the urinary
pharmacokinetics of THCCOOH in humans after oral THC administration. Varying THC doses were administered through
gelatin capsule and liquid hemp oil, along with THC in sesame
oil, to examine effects due to dose, vehicle type and form. This
study also reports on elimination half-life determinations for
the terminal phase of urinary THCCOOH excretion and excretion prior to a 15 ng/mL cutoff.
Materialsand Methods
Participants
Seven healthy participants with a history of marijuana use
resided on the secure clinical research unit of the Intramural
Research Program (IRP), National Institute on Drug Abuse
(NIDA), National Institutes of Health while participating in a
protocol designed to characterize the pharmacokinetics and
pharmacodynarnicsof oral THC. The NIDAInstitutional Review
Board approved the study. All subjects provided written informed consent, were under continuous medical supervision,
and were financially compensated for their participation. Subject characteristics and drug use histories were previously described (24).
Prior to admission, each participant underwent thorough
medical (physical exam, ECG, blood, and urine chemistries)
and psychological evaluations, including past and recent drug
use history. Participants did not receive the first drug administration until urine cannabinoid concentrations were below 10
ng/mL by fluorescence polarization immunoassay (Abbott Laboratories, Abbott Park, IL). TWenty-four-hourmedical surveillance and a closed, secure ward prevented access to unauthorized licit or illicit drugs. In addition, weekly urine drug tests
for amphetamines, cannabinoids, cocaine, opiates, and phencyclidine were performed.
161
Journal of Analytical Toxicology, Vol. 28, April 2004
Drug administration
This protocol was a randomized, double blind, double
dummy, placebo-controlled clinical study. Double dummy
refers to the fact that liquid oil and capsules were administered
at each time point, although at most one of the dosage forms
contained active cannabinoids. Neither research personnel nor
participant were aware of drug content, thus the term double
blind. Each subject participated in five dosing conditions. Each
entailed supervised administration of 15 mL (approximately
one tablespoon) hemp oil and two capsules three times per day
with meals for five consecutive days. Subjects freely selected
food choices, without restriction, from the clinical research
unit menus. After 5 consecutive dosing days, there was a 10-day
washout period. Individuals resided on the secure clinical unit
for 10 to 13 weeks.
Dosing conditions were randomized and assigned by the
IRP's pharmacy to ensure that research staff and participants
were blind to the administered dose. The five dosing conditions
were as follows: 1. placebo oil and placebo capsules; 2. low
dose hemp oil and placebo capsules; 3. high dose hemp oil
and placebo capsules; 4. placebo oil and low dose capsules;
and 5. placebo oil and dronabinol capsules. The hemp oil capsules and dronabinol capsules were contained within larger
capsules to maintain double blind conditions.
Hemp oils were assayed by GC-MS to accurately determine
the concentration of THC. Flax oil was administered as the
placebo. The liquid low-dose hemp oil contained 9 pg/g THC
for a total daily dose of 0.39 mg. The low-dose hemp oil administered in capsules contained 92 pg/g THC for a total dose
of 0.47 mg/d. A total daily dose of 14.8 mg was achieved with
the liquid high dose hemp oil (concentration 347 IJg/g THC).
Dronabinol (synthetic THC in sesame oil), 2.5 mg THC per capsule, was administered as a positive control with a daily total
dose of 7.5 rag. For safety reasons, only 5.0 mg THC was administered on the first dosing day of the session. Doses administered reflected concentrations of THC in commercially
available hemp oil at the time of study design.
Analytical analysis
Every urine void was collected from admittance to discharge
from the clinical unit. Specimens (N = 4381) were collected in
polypropylene containers, refrigerated immediately after urination, and measured for total volume. Aliquots of urine specimens were stored at -20~ within 48 h of collection. After the
protocol was completed, frozen specimens were assembled and
coded. Specimens were randomized within a large batch to
eliminate potential analytical bias. Samples were assayed immediately after thawing and mixing; each specimen underwent only one freeze-thaw cycle. Specimens were analyzed
within one to two years of collection for total THCCOOH by
GC-MS, with a limit of detection of 2.5 ng/mL, according to a
published procedure (25,26). Aliquots from each specimen
also were analyzed for creatinine (Roche Diagnostic, Indianapolis, IN) on a Hitachi 704 automated clinical analyzer
(Roche Diagnostic, Montclair, NJ). Each batch of samples contained assayed negative and positive blind controls.
Creatinine normalized values for urinary THCCOOH excretion were calculated by dividing the THCCOOH concentration
162
(ng/mL) by the creatinine concentration (mg/mL) to yield the
normalized THCCOOH concentration (ng/mg).
Pharmacokinetic and data analysis
Elimination half-lives (tl/~) were calculated as tl/2 = ln2/~,
where the elimination rate constant (~.)was calculated from the
slope of the terminal portion of the semilogarithmic excretion
rate-time curve by linear regression analysis. Pharmacokinetic
parameters were derived by noncompartmental methods with
the use of WinNonlin Professional software (Ver.3.2; Pharsight
Co.). There was uniform weighting of all data points. A minimum of six and a maximum of twelve points on the excretion
rate-time curve were used in the half-life determination.
To determine the percentage of total dose excreted as THCCOOH, the molar equivalent dose of THC to THCCOOH was
calculated for each dosing session. The adjusted total dose was
divided by the cumulative amount of THCCOOH excreted
throughout each individual dosing session.
Data are represented as mean plus or minus standard deviation (SD). Statistical analysis was performed by SPSS software
(Ver. 10.0; SPSS Inc.). Data were analyzed employing t-test
statistics. Statistical significance was assumed when P was _<
0.05. Paired t-tests were performed on nonrandomized factors
when effects were significant.
Results
Urine THCCOOH excretion profile
Figure 1 is the urinary excretion profile for Subject A for five
THC dosing sessions and the initial washout phase. The
washout phase was necessary to allow excretion of cannabinoid
metabolites from cannabis use prior to admission to the secure
research unit. Order of dose administration was randomized
between participants and included a placebo dose for pharmacodynamic assessments. Seven participants produced an average of 626 • 122.8 urine specimens over the entire study protocol, including the initial washout period. Mean maximum
THCCOOH and concentration ranges for daily doses of 0.39,
0.47, 7.5, and 14.8 mg THC were 19.8 • 13.1 (7.3-38.2), 12.2
• 9.6 (5.4-31.0), 145.7 • 143.4 (26.0-436.0), and 116.0 • 93.2
(19.0-264.0) ng/mL, respectively.
Pharmacokinetic parameters of
urinary THCCOOH excretion
Mean urinary terminal elimination half-lives averaged 50.3
+ 17.4, 44.2 • 19.4, 64.0 • 22.5, and 52.1 + 21.8 h following
daily doses of 0.39, 0.47, 7.5, and 14.8 mg THC, respectively
(Table I). The half-lives were calculated from the terminal
phase of the excretion rate curve for each subject after the
last dose. The excretion rate curve for Subject A at the 7.5
mg/d dose is presented in Figure 2A. The dark line indicates the
data used in predicting the terminal elimination half-life.There
were no significant differences in mean terminal elimination
half-lives for the four doses. Up to a fourfold intrasubject variation across doses and a sixfold intersubject variation for a
single dose in terminal elimination half-liveswere observed.
Journal of Analytical Toxicology, Vol. 28, April 2004
IOO
100
$0
5OO
_
-
lOOO
]SOO
-
El
Time (b)
Figure 1.11-Nor-9-carboxy-A9-tetrahydrocannabinol urinary excretion
profile of Subject A over five oral A%tetrahydrocannabinol dosing sessions. Each point representsa single urine specimen. Arrows indicate dose
and time of session initiation. The 0.47 and 7.5 rag/day doses were delivered in capsule form with the 0.39 and 14.8 rag/day doses delivered in
liquid form. Excretion of previously self-administered cannabinoids indicated by asterisk (*).
Elimination half-lives were determined also from an earlier
phase of the excretion curve, from the last dose to the last
urine sample with a THCCOOH concentration cutoff of > 15
ng/mL. These half-life data are presented in Table II for the two
high doses. Mean apparent half-lives of 24.1 • 7.8 and 21.1 •
4.3 h were found for the 7.5- and 14.8-mg daily doses, respectively. These times were significantly different (P < 0.05) from
their respective terminal elimination half-lives. Figure 2B illustrates the shorter elimination half-life found in this portion
of the excretion curve. There was an approximate 60% decrease in half-lives when the final concentration endpoint was
increased to 15 ng/mL.
Urinary excretion rate curves also were generated from THCCOOH concentrations normalized to urinary creatinine concentrations (data not shown). Terminal elimination half-lives
were not significantly different from non-normalized elimination data. Also, no significant differences were found in other
pharmacokinetic parameters, that is, maximum excretion rate
and time of maximum excretion rate, between the non-norrnalized and creatinine-normalized data. Non-normalized mean
maximum excretion rates during three times daily dosing were
Table I. Urinary 11-Nor-9-Carboxy.L~%Tetrahydrocannabinol Terminal Elimination Half-Lives (h) after Oral
Ag-Tetrahydrocannabinol
Elimination Haft.lives (h)
14.8 rag/day
(Liquid)
N
~bjed
N*
7.5 rag/day*
(Capsule)
N
A
C
G
H
L
N
P
12
9
12
6
9
10
7
61.5
79.4
88.8
23.6
49.4
82.1
63.2
6
6
6
8
7
8
7
64.8
79.3
25.6
23.9
81.0
45.0
45.3
-
64.0 (22.5)
-
52.1 (21.8)
Mean (• SD)
0.47 mg/day
(Capsule)
N
0.39 mg/day
(Liquid)
12
8
6
6
7
6
6
51.7
59.0
34.7
11.6
65.0
58.0
29.5
7
9
7
6
10
10
6
44.2
84.1
31.4
59.8
45.8
37.6
48.7
-
44.2 (19.4)
-
50.3 (17.4)
* Number of points on excretion curve usedto determineterminal elimination half-life.
I
* Dronab'nol,
syntheticA9-tetrahydrocannabinol,2.5 mg THC capsules.
,=]
A
O
10000]
t
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ONer~d
10000
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o o,.~Po
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~~176 2
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100000
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O QD
O
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-
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o
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IO0
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10
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10
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50
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150
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200
~pol::t (h)
i
250
i
300
1
350
0
i
50
t
100
t
180
J
200
i
260
t
300
i
380
Mktpeim(h)
Figure 2. Urinary excretion rate curve for 7.5 mg/d dose for Subject A with black line indicating section of curve used to predict terminal elimination half-life
(A). Urinary excretion rate curve for 7.5 mg/d dose for Subject A with black line indicating section of line, prior to last urine sample with a THCCOOH concentration ~ 15 ng/mL, used to determine apparent elimination half-life (B).
163
Journal of Analytical Toxicology, Vol. 28, April 2004
0.26 • 0.22, 0.09 • 0.06, 1.6 • 1.8, and 0.68 • 0.39 ng/h for the
0.39, 0.47, 7.5, and 14.8 mg/d doses, respectively. The mean
time to maximum excretion rates from non-normalized data
ranged from 67.4 • 29.0 to 94.9 • 69.0 h.
Percent of total dose excreted as THCCOOH
When expressed as a percentage of the total available THC
dose, and corrected for molar equivalents, the low THC daily
doses generally had a higher percentage excreted in 14 days
than did the two high daily doses (Figure 3). Mean percentages
of total THC dose excreted were 2.5 • 2.7, 2.9 • 1.6, 1.5 • 1.4,
and 0.6 • 0.5% with ranges of 0.7-8.1, 1.4-4.6, 0.4-4.4, and
0.2-1.5% for the 0.39, 0.47, 7.5, and 14.8 mg/d doses, respectively. The highest percent total dose excreted was 8.1% by participant C following the 0.47 mg/d dose, and the lowest percent
excreted was 0.2% by participant L at the 14.8-mg daily dose.
A higher intersubject variability was observed with the capsulated doses, 0.47 and 7.5 mg/d THC, than when THC was delivered in 15-mL hemp oil doses, 0.39 and 14.8 mg/d THC.
There were significance differences (P _<0.05) in the mean
percent total dose excreted between the dronabinoi (7.5 mg/d)
and the high liquid hemp oil dose of 14.8 rag/d, and between
the high and low liquid doses.
Discussion
There is a need to improve our knowledge of cannabinoid
pharmacokinetics after oral administration. It is vitally important for developing potential therapeutic uses and for understanding oral cannabis abuse. Although cannabinoid research has expanded since THC was identified as the primary
psychoactive constituent (27), the recent discovery of a mammalian endocannabinoid system emphasizes the need for
further research.
Table II. Apparent* 11-Nor-9-Carboxy-AgTetrahydrocannabinol Urinary Elimination Half-Life (h)
for GC-MS Cutoff of 15 ng/mL after Oral A9Tetrahydrocannabinol
THC metabolites are almost exclusivelyeliminated from the
body in urine and feces, with about one-third of the absorbed
dose excreted in the urine and the remainder in the feces
(14,28). William and Moffat (29), in 1980, identified the THCCOOH glucuronide conjugate as the major urinary metabolite
of THC in humans. In this study, we chose to examine the urinary excretion of THCCOOH, not only because it is the primary
metabolite, but also because it is the analyte most often quantified in urinalysis drug testing for detection of cannabis exposure. Closed clinical conditions were utilized to obtain the
most reliable data. Access to outside drugs that may have confounded results was eliminated. Also, every urine void was collected and analyzed providing detailed information not obtainable from studies of 24-h pooled samples or when only
single daily specimens are tested.
Previous reports have indicated low bioavailabilityafter oral
THC administration due to poor absorption, degradation by
gastric acid, and biotransformation to metabolites prior to systemic circulation (6,7). Unlike the inhalation route, THC absorbed from the gastrointestinal system has considerable first
pass metabolism in the liver. THC is extensively biotransformed
by Cytochrome P450enzymes, decreasing the amount of available THC for systemic distribution. Absorption of THC from the
gut is slow and erratic with peak plasma concentrations occurring between 1 to 6 h (13-15). Ohlsson et al. (13) found
variable peak plasma concentrations of 4.4 to 11 ng/mL from
60 to 300 rain after ingestion of a cookie containing 20 mg
THC. One factor, which can influence a drug's absorption
across the gut, is degradation by gastric acids (30). Several
competing reactions may occur within the stomach's low pH
environment including isomerization of THC to the thermodynamically more stable AS-tetrahydrocannabinol or protonation of the oxygen in the pyran ring resulting in ring cleavage
to cannabidiol (6,31).
This study examined the percent total THC dose excreted as
THCCOOH in urine. Previous studies have examined the urinary excretion of combined THC metabolites after oral dosing.
In 1972, Perez-Reyes et al. (16) reported a range of 18.3 + 6.9
to 21.9 • 4.2% for mean percentage of total dose excreted in
urine as cannabinoids, following oral dosing using five dif9T
EliminationHalf-Lives(h)
8
Subject
N~
A
C
G
H
L
N
P
Mean (_ SD)
6
9
10
6
7
6
10
*
*
7.5 mg/day*
(Capsule)
N
14.8 mg/day
(Liquid)
16.3
36.7
32.6
22.0
18.0
18.9
24.3
24.1 (7.8)
9
9
9
6
12
8
7
-
22.8
22.0
24.6
26.2
19.0
13.0
20.5
21.1 (4.3)
Calculatedfrom excretion rate curve prior to last urine samplewith a 11-nor-9carboxy-Ag-tetrahydrocannabinolconcentration> 15 ng/mL by GC-MS.
Number of points on excretioncurve usedto determineapparentelimination
half-tile.
Dronabinol, syntheticA~-tetrahydrocannabinol,2.5 mg capsules.
164
7
6
'Lt L
A
C
G
YI
L
N
P
Mean
Subjects
Figure 3. Percentages of total Ag-tetrahydrocannabinol dose, calculated as
the 11-nor-9-carboxy-A9-tetrahydrocannabinol molar equivalents, excreted
in urine over t4 days during and after oral Ag-tetrahydrocannabino] doses.
Journal of Analytical Toxicology, Vol. 28, April 2004
ferent vehicles to deliver THC. Sadler and Wall (32) reported a
21 • 1% cumulative excretion of radiolabeled cannabinoids in
urine after 72 h, following a 20-rag THC oral dose in sesame
oil. Wall et al. (14) observed mean cumulative cannabinoid
excretion after 72 h of 15.9 • 3.6 and 13.4 • 2.0% following
oral doses in sesame oil to women (15 mg THC) and men (20
mg THC), respectively. Halldin et al. (19) reported that of the
approximately 20% of dose eliminated as acidic urinary
metabolites, 27% was conjugated and unconjugated THCCOOH.
Mean percentages of total THC dose excreted as THCCOOH
metabolite were 2.5 • 2.7 and 1.5 • 1.4% for the 0.47 and 7.5
mg/d THC doses in capsules, respectively;and 2.9 • 1.6 and 0.6
• 0.5%, for 0.39 and 14.8 mg THC daily doses in liquid form,
respectively. These data are in close agreement with those reported by Cone et al. (33). After ingestion of 22.4 and 44.8 mg
THC in cannabis brownies, a mean of 1.3% of the total THC
dose was excreted in the urine. Although not an oral dosing
study, Huestis et al. (23) observed similar THCCOOHexcretion
percentages, 0.54 • 0.1 and 0.53 • 0.1%, of total dose following smoking of low and high-dose marijuana cigarettes.
In our study, significant differences (P _r 0.05) were observed for the mean percent of dose excreted between the
capsulated 7.5 mg/d THC high dose (1.46 • 1.41%) and the
14.8 mg/d liquid dose in hemp oil (0.55 • 0.46%). Also, there
was a significant difference in percent excreted between the
14.8 mg/d liquid hemp oil dose and the 0.47 mg/d capsulated
dose (2.51 • 2.73%). It is difficult to ascertain if the significant
differences observed in this study are of clinical significance,
in that, no differences were found between the other combinations of doses. The dronabinol dose had a significantly larger
percentage of THCCOOH excreted in urine than the high
hemp oil dose (Figure 3), indicating improved bioavailability.
There are two possible explanations, one is that the capsule
provides protection against degradation by stomach acids, allowing for a larger portion of THC to pass into the small intestine for absorption. Also, the high molecular weight sesame
oil may in someway improve THC absorption. Perez-Reyes et
al. (16), dissolved THC in five different vehicles and delivered
each in gelatin capsules. The vehicle that produced the highest
plasma cannabinoid concentration was sodium glycocholate
followed by sesame oil. The authors concluded that the speed
and degree of absorption were greatly influenced by the vehicle. However, it also was noted that even with the same vehicle, drug absorption demonstrated considerable intersubject
variability.
Late in excretion, a urine sample may be positive, above a
certain cutoff, then negative and then positive again; the hydration level of an individual influences urine drug concentrations. This problem of fluctuating THCCOOHconcentration
has been addressed by normalizing metabolite concentration to
urine creatinine concentration, a method intended to reduce
variability of analyte concentration attributed to dilution.
Huestis and Cone (34) examined creatinine normalization of
urinary THCCOOHto differentiate between residual metabolite
excretion and new marijuana use; a situation of considerable
importance to drug testing and drug-treatment programs. No
study to date has examined the effect of creatinine norrnaliza-
tion on THCCOOH pharmacokinetic parameters. This study
compared pharmacokinetic parameters: half-life, maximum
excretion rate and time to maximum excretion rate, between
non-normalized and normalized creatinine data. No significant
differences (P _r 0.05) were observed between the two sets of
data for three parameters at four different doses.
The rate-limiting step in the elimination of THC from the
body is the redistribution of THC from tissue depots back into
circulation (35). Urinary half-lives were determined from the
terminal phase of the excretion rate-time curve for each subject, after 15 THC doses over five days, with four different THC
doses. No significant differences (P ~ 0.05) in mean terminal
elimination half-lives (range: 44.2 • 19.4 to 64.0 + 22.5 h)
were observed across doses. These results are similar to urinary
THCCOOH terminal elimination half-lives reported in previous smoking and oral dosing studies (17,18,21).
Johansson et al. (21) conducted a study to determine the urinary excretion half-life of THCCOOH in heavy marijuana users
following smoking of two marijuana cigarettes, each containing 15 mg THC. A mean urinary excretion half-life of 72.0
• 55.2 h was found with monitoring times extending as long as
25 days in one of the subjects. In a subsequent study (17), urinary THCCOOHexcretion half-lives of 14.5 and 17.7 h were estimated from urine samples collected between 24 to 48 h and
48 to 72 h after an oral dose of 20 mg THC. The authors also reported a 32.4 h urinary THCCOOH excretion half-life in one
subject after smoking a 19 rng THC cigarette and monitoring
for 120 h monitoring period. These two studies demonstrate a
considerable range in urinary THCCOOH excretion half-lives.
In 1998, Huestis et ai. reported elimination half-lives after
smoking 15.8 mg and 33.8 mg THC cigarettes of 31.5 •
h
and 28.6 • 1.5 h, respectively, after monitoring urinary THCCOOH excretion for seven days (18). They also reported longer
half-lives of 52.8 • 3.4 h for the high dose when the monitoring
period was extended to 14 days. The urinary THCCOOH terminal elimination half-lives observed in the present study with
a ten day monitoring period are in close agreement to previously reported studies. However, the area of the excretion rate
curve used in the determination may influence estimates significantly.
Researchers studying THC plasma elimination have reported
a polyphasicTHC excretion rate curve (6). Barnett et al. (36) reported a triexponential function to describe plasma-time data
for the elimination of THC following smoking of two 1% THC
cigarettes in six subjects. The "apparent terminal half-life" is
determined from an earlier portion of the excretion rate curve.
Examination of urinary THCCOOH excretion profiles (Figure
1) reveals a minimum of biphasic elimination. In our study,
two half-life estimates, terminal elimination, and apparent
elimination to 15 ng/mL, were determined for the dronabinol
dose, using the terminal phase of the excretion rate-time curve
and the segment of the curve just prior to the last urine sample
with a THCCOOH concentration of 15 ng/mL. The same analysis was performed with the high hemp oil dose of 14.8 mg/d
THC. There was more than a twofold decrease in the apparent
half-lives, 24.1 • 7.8 and 21.1 • 4.3 h, as compared to the terminal elimination half-lives, 64.0 • 22.5 and 52.1 • 21.8 h, for
THC daily doses of 7.5 and 14.8 rag, respectively. These data
165
Journal of Analytical Toxicology,Vol. 28, April 2004
demonstrate similar results as observed in THC plasma kinetic
studies.
Estimates of urinary THCCOOH elimination half-life are
used by forensic toxicologists to evaluate possible cannabis
exposure scenarios based on urine THCCOOHconcentrations.
This is not an uncommon occurrence for an expertwitness involved in urine drug testing programs. However for a urine
sample to be reported positive for cannabinoids, it generally
must have a THCCOOHconcentration > 15 ng/mL by GC-MS;
anything below that value is considered a negative specimen.
If half-lives used to evaluate these scenarios are based on estimates determined from the terminal area of the excretion
curve that consists of lower THCCOOHconcentrations, these
longer half-life estimates may not reflect elimination rates
prior to THCCOOHconcentrations > 15 ng/mL. The measured
elimination half-life for THCCOOHwill vary based on the area
of the excretion curve monitored. As the sensitivity of analytical methods and monitoring time increase, longer terminal
elimination half-life estimates are obtained.
This study provides pharmacokinetic data on the urinary
excretion of THCCOOHfollowing controlled oral administration. These data demonstrate that the apparent urinary elimination tlr2 of THCCOOHprior to reaching a 15 ng/mL concentration is significantly shorter than the terminal urinary
elimination tl/2. These controlled drug administration data
should assist in the interpretation of urine cannabinoid results and provide clinicians with valuable information for future pharmacological studies.
Acknowledgments
We thank David Darwin, Debbie Price, and the clinical staff
of the NIDA IRP Research Unit for their technical assistance.
We are grateful also to Carole Trojan, Erick Fitzer, and the Navy
Drug Screening Laboratory Jacksonville Screening and Confirmation staff for analytical assistance in this project. We
would also like to thank the Research Triangle Institute for the
GC-MS analysis of the hemp oil and the Department of Defense, Department of Transportation, Substance Abuse and
Mental Health Services Administration, and NIDA IRP for
funding this project.
References
1. L. Iversen. High times for cannabis research. Proc. Natl. Acad. Sci.
96:5338-5339 (1999).
2. 1-. Lehmann, F. Sager, and R. Brenneisen. Excretion of cannabiholds in urine after ingestion of cannabis seed oil. J. Anal. Toxicol.
21:373-375 (1997).
3. T.Z. Bosy and K.A. Cole. Consumption and quantitation of A9tetrahydrocannabinol in commercially available hemp seed oil
products. J. Anal. Toxicol. 24:562-566 (2000).
4. N. Fortner, R. Fogerson, D. Lindman, T. Iversen, and D. Armbruster. Marijuana-positive urine test results from consumption of
hemp seeds in food products. J. Anal Toxicol. 21:476-481
(1997).
166
5. A. Air and G. Reinhardt. Positive cannabis results in urine and
blood samples after consumption of hemp food products. J. Anal.
Toxicol. 22:80-81 (1998).
6. D.J. Harvey and W.D.M. Paton. Metabolism of the cannabinoids.
Rev. Biochem. Toxicol. 6:221-264 (1986).
7. M.A. Peat. Distribution of delta-9-tetrahydrocannabinol and its
metabolites. In Advances in Analytical Toxicology II. R.C. Baselt,
Ed. Year Book Medical Publishers, Chicago, IL, 1989, pp
186-217.
8. R.E. Struempler, G. Nelson, and F.M. Urry. A positive cannabiholds workplace drug test following the ingestion of commercially
available hemp seed oil. J. Anal ToxicoL 2t: 283-285 (1997).
9. J.C. Callaway, R.A. Weeks, L.P. Raymon, H.C. Walls, and W.L.
Hearn. A positive THC urinalysis from hemp (Cannabis) seed
oil. J. Anal. Toxicol. 21: 319-320 (1997).
10. A. Costantino, R.H. Schwartz, and P. Kaplan. Hemp oil ingestion
causes positive urine tests for Ag-tetrahydrocanabinol carboxylic
acid. J. Anal. Toxicol. 21: 482-485 (1997).
1t. G. Leson, P. Pless, F. Grotenhermen, H. Kalant, and M.A. EISohly. Evaluating the impact of hemp food consumption on workplace drug tests. J. Anal. ToxicoL 25:691-698 (2001).
12. Interpretation of listing of "Tetrahydrocannabinols" in Schedule I,
Interpretive rule. Fed. Regist. 66(195)" 51530-51544 (2001).
13. A. Ohlsson, J.E. Lindgren, A. Wahlen, S. Agurell, L.E. Hollister,
and H.K. Gillespie. Plasma delta-9-tetrahydrocannabinol concentrations and clinical effects after oral and intravenous administration and smoking. Clin. Pharmacol. Ther. 28:409-416 (1980).
14. M.E. Wall, B.M. Sadler, D. Brine, H. Taylor, and M. Perez-Reyes.
Metabolism, disposition, and kinetics of delta-9-tetrahydrocannabinol in men and women. Olin. Pharmacol. Ther. 34"
352-363 (1983).
15. B. Law, P.A. Mason, A.C. Moffat, R.I. Gleadle, and L.J. King.
Forensic aspects of the metabolism and excretion of cannabinoids
following oral ingestion of cannabis resin. J. Pharm. Pharmacol.
36:289-294 (1984).
16. M. Perez-Reyes, M.A. Lipton, M.C. Timmons, M.E. Wall, D.R.
Brine, and K.H. Davis. Pharmacology of orally administered
delta-9-tetrahydrocannabinol. Clin. Pharmacol. Ther. 14:48-55
(1973).
17. E. Johansson, H.K. Gillespie, and M.M. Halldin. Human urinary
excretion profile after smoking and oral administration of [14C]
delta-l-tetrahydrocannabinol. J. Anal. Toxicol. 14:176-180
(1990).
18. M.A. Huestis and E.J.Cone. Urinary excretion half-life of 11-nor9-carboxy-delta-9-tetrahydrocannabinol in humans. Ther. Drug
Monit. 20:570-576 (1998).
19. M.M. Halldin, M. Widman, S. Agurell, L.E. Hollister, and S.U
Kanter. Acidic metabolites of delta-l-tetrahydrocannabinol excreted in the urine of man. In The Cannabinoids: Chemical, Pharmacologic and Therapeutic Aspects, S. Agurell, W.L. Dewey,
and R.E. Willette, Eds. Academic Press, New York, NY, t984, pp
211-218.
20. L.I. McBurney, B.A. Bobbie, and L.A. Sepp. GC/MS and Emit
analyses for delta-9-tetrahydrocannabinol metabolites in
plasma and urine of human subjects. J. Anal. Toxicol. 10:
56-64 (1986).
21. E. Johansson and M.M. Halldin. Urinary excretion half-life of
deltal-tetrahydrocannabinol-7-oic acid in heavy marijuana users
after smoking. J. Anal. Toxicol. 13:218-223 (1989).
22. P. Kelly and R.T.Jones. Metabolism of tetrahydrocannabinol in frequent and infrequent marijuana users. J. Anal. Toxicol. 16"
228-235 (1992).
23. M.A. Huestis, J.M. Mitchell, and E.J. Cone. Urinary excretion
profiles of 11-nor-9-carboxy-Ag-tetrahydrocannabinol in humans
after single smoked doses of marijuana. J. Anal. Toxicol. 20"
441-452 (1996).
24. R. Gustafson, B. Levine, P.R. Stout, K.L. Klette, M.P. George, E.T.
Moolchan, and M.A. Huestis. Urinary cannabinoid detection
times following controlled oral administration of Ag-tetrahydrocannabinol to humans. Cfin. Chem. 49(7): 1114-1124 (2003).
Journal of Analytical Toxicology,Vol. 28, April 2004
25. R. Mechoulam. Recent advances in cannabinoid research. Forsch
Komplementarmed 6:16-20 (1999).
26. P.R.Stout, C.K. Horn, and K.L. Klette. Solid-phase extraction and
GC-MS analysis of THC-COOH method optimized for a highthroughput forensic drug-testing laboratory. J. Anal Toxicol. 25:
550-554 (2001).
27. R. Mechoulam and Y. Gaoni. A total synthesis of dl-delta-1tetrahydrocannabinol, the active constituent of hashish. J. Am.
Chem. Soc. 87:3273-3274 (1965).
28. C.A. Hunt and R.T. Jones. Tolerance and disposition of tetrahydrocannabinol in man. J. PharmacoL Exp. Ther. 215:35-44
(1980).
29. P.L.Williams and A.C. Moffat. Identification in human urine of
delta-9-tetrahydrocannabinol-11-oic glucuronide: a tetrahydrocannabinol metabolite. J. Pharm. PharmacoL 32:445-448 (1980).
30. S. Agurell, M. Halldin, J.E. Lindgren, A. Ohlsson, M. Widman, H.
Gillespie, and L. Hollister. Pharmacokinetics and metabolism of
delta-tetrahydrocannabinol and other cannabinoids with emphasis on man. Pharmacol. Rev. 38:21-43 (1986).
31. E.R.Garrett and C.A. Hunt. Physiochemical properties, solubility,
and protein binding of delta-9-tetrahydrocannabinol. J. Pharm.
Sci. 63:1056-1064 (1974).
32. B.M. Sadler, M.E. Wall, and M. Perez-Reyes. The pharmacokinetics of delta-9-tetrahydrocannabinol in after simultaneous intravenous and oral administration. The Cannabinoids: Chemical
Pharmacologic and Therapeutic Aspects, S. Agurell, W.L. Dewey,
and R.E. Willette, Eds. Academic Press, New York, NY, 1984, pp
227-238.
33. E.J.Cone, R.E.Johnson, B.D. Paul, L.D. Mell, and J. Mitchell. Marijuana-laced brownies: behavioral effects, physiologic effects,
and urinalysis in humans following ingestion. J. AnaL ToxicoL 12:
169-175 (1988).
34. M.A. Huestis and E.J. Cone. Differentiating new marijuana use
from residual drug excretion in occasional marijuana users.
J. Anal. Toxicol. 22:445-454 (1998).
35. E.R. Garrett and C.A. Hunt. Pharmacokinetics of delta-9-tetrahydrocannabinol in dogs. J. Pharm. Sci. 66:395-406 (1977).
36. G. Barnett, C.W.N. Chiang, M. Perez-Reyes, and S.M. Ownes.
Kinetic study of smoking marijuana. J. Pharm. Biopharm. 10:
495-506 (1982).
Manuscript received April 15, 2003;
revision received July 23, 2003.