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. 2009 Dec;104(12):2041-8.
doi: 10.1111/j.1360-0443.2009.02705.x. Epub 2009 Oct 5.

Do Delta9-tetrahydrocannabinol Concentrations Indicate Recent Use in Chronic Cannabis Users?

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Do Delta9-tetrahydrocannabinol Concentrations Indicate Recent Use in Chronic Cannabis Users?

Erin L Karschner et al. Addiction. .
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Abstract

Aims: To quantify blood Delta(9)-tetrahydrocannabinol (THC) concentrations in chronic cannabis users over 7 days of continuous monitored abstinence.

Participants: Twenty-five frequent, long-term cannabis users resided on a secure clinical research unit at the US National Institute on Drug Abuse under continuous medical surveillance to prevent cannabis self-administration.

Measurements: Whole blood cannabinoid concentrations were determined by two-dimensional gas chromatography-mass spectrometry.

Findings: Nine chronic users (36%) had no measurable THC during 7 days of cannabis abstinence; 16 had at least one positive THC > or =0.25 ng/ml, but not necessarily on the first day. On day 7, 6 full days after entering the unit, six participants still displayed detectable THC concentrations [mean +/- standard deviation (SD), 0.3 +/- 0.7 ng/ml] and all 25 had measurable carboxy-metabolite (6.2 +/- 8.8 ng/ml). The highest observed THC concentrations on admission (day 1) and day 7 were 7.0 and 3.0 ng/ml, respectively. Interestingly, five participants, all female, had THC-positive whole blood specimens over all 7 days. Body mass index did not correlate with time until the last THC-positive specimen (n = 16; r = -0.2; P = 0.445).

Conclusions: Substantial whole blood THC concentrations persist multiple days after drug discontinuation in heavy chronic cannabis users. It is currently unknown whether neurocognitive impairment occurs with low blood THC concentrations, and whether return to normal performance, as documented previously following extended cannabis abstinence, is accompanied by the removal of residual THC in brain. These findings also may impact on the implementation of per se limits in driving under the influence of drugs legislation.

Conflict of interest statement

The authors have no conflicts of interest to report.

Figures

Figure 1
Figure 1
Detection rate percentages of Δ9-tetrahydrocannabinol (THC), 11-hydroxy-9-THC (11-OH-THC) and 11-nor-9-carboxy-THC (THCCOOH) in whole blood of participants (N = 25) over 7 days of continuously monitored cannabis abstinence. LOQ for THC and THCCOOH 0.25 ng/mL and 11-OH-THC 0.50 ng/mL.
Figure 2
Figure 2
Representative patterns of Δ9-tetrahydrocannabinol (THC) (◊), 11-hydroxy-9-THC (11-OH-THC) (■) and 11-nor-9-carboxy-THC (THCCOOH) (▲) excretion. Participant O (panel A), U (panel B) and S (panel C) whole blood cannabinoid concentrations during 7 days of continuously monitored cannabis abstinence.

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