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The dose absorbed after having smoked a cannabis joint
varies between 5 and 30 mg. The plasma concentration of tetrahydrocannabinol (THC) presents a very fast peak (about 3 to
8 minutes) and then decreases quickly (half-life of approximately
30 minutes). THCCOOH has a much longer half-life, about 20 to 57
hours in occasional users and 3 to 13 days in regular users.
THC is detectable (LOD 1 ng/mL) for approximately 5 hours
in plasma and 10 hours in urine (LOD 10 ng/mL).
THCCOOH can be detected much longer, and a detection time (LOD 5
ng/mL) of 25 days has been reported.
A study carried out in Lübeck with 52 volunteers admitted to a detoxification ward showed that THCCOOH (LOD 10 ng/mL) remained detectable in serum on average for 23.8 hours, and 49 hours to the
After smoking a 1.75% or 3.55% THC cigarette, the last
positive (15 ng/mL THCCOOH by GC-MS) urine sample was
found at 33.7 ± 9.2 hours and 88.6 ± 9.5 hours, respectively.
After smoking marihuana, urine tested positive consecutively
for average periods of 26 ± 9 (extreme values 2–72) hours with
EIA and 33 ± 10 (extreme values 4–72) hours with GC-MS.
The average THCCOOH detection times of the last positive
specimen were 42 ± 10 (extreme values 2–72) and 58 ± 6 (extreme
values 16–72) hours by EIA and GC-MS, respectively.
After a subject smoked a joint containing 1.75% THC, urine
was positive (cutoff > 20 ng/mL, EMIT) for 2.1 days; after
a joint with 3.5% THC, the detection time was 3.8 days.
Creatinine normalization of the THCCOOH values gives
smoother excretion curves than THCCOOH concentrations
alone, but even after normalization considerable variation between
consecutive specimens remains.
Criteria were established for differentiating new drug use from residual excretion, and these were evaluated by other authors.
After oral intake, the detection time in urine seems to be
longer, eg, after intake of 2 brownies containing 2.8% THC,
the metabolite could be detected by EMIT (cutoff 20 ng/mL)
for 5.9 days.
In chronic users, the inactive metabolite (THCCOOH) can be detected for weeks or even months.
The study by Lübeck in 52 volunteers admitted to a detoxification
ward showed that THCCOOH (LOD10 ng/mL) remained detectable
in urine for 4.9 days on average and 18 days to the maximum.
The longest reported detection times are 93 days and
95 days, but these are probably exceptional cases.
Niedbala et al measured the salivary concentrations of
THC after oral administration or smoking of marihuana. The
LOD were, respectively, 1 ng/mL and 0.5 ng/mL for ELISA
and gas chromatography–tandem mass spectrometry (GCMS-
MS). All the analyses were positive for up to 15 hours
(range 1–24) by ELISA and 13 hours (1–24) by GC-MS-MS.
The detection times (last positive sample) were 31 hours (1–
72) by ELISA and 34 hours (1–72) by GC-MS-MS.
In this study THCOOH was positive in urine for 58 hours (16–72
hours). However, the subjects were not supervised during the
whole study, and some of them could have taken supplementary
doses after supervision ended.