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Cannabinoids in hair: strategy to prove marijuana/hashish consumption
by Uhl M, Sachs H.


Delta(9)-Tetrahydrocannabinol (THC) and 11-nor-Delta(9)-tetrahydrocannabinol-9-carboxylic acid (THCA) are equally used to indicate consumption of cannabis (hashish and marijuana). Publications of the early 90's demonstrate the possibilities of determining THC, cannabinol (CBN), and cannabidiol (CBD). All these substances are present in cannabis smoke and can be incorporated into the hair only by contamination. Generally, washing procedures should prevent false positive results, but finally it cannot be excluded that traces of THC may be found in hair after mere passive cannabis smoke exposure. Three authentic cases illustrate the problems originating in the exclusive determination of THC/CBN. The first example is the case of a couple living together in an apartment. Both persons' hair samples had been taken and gave positive results for THC and CBN. The male subject admitted smoking cannabis several times per day, but the female mate denied any consumption. Examination of the hair for THCA showed a high level (>6.6pg/mg) in the sample of the male person and negative results (LOQ 0.1pg/mg) in the sample of his mate. The second case hair is of a self admitted cannabis user's hair and was tested first by an immunoassay and GC/MS with a negative result. Nevertheless, the THCA concentration quantified in his sample was 2.7pg/mg hair. The third hair sample is of a 2-year-old child that was tested positive for cannabis by using an immunochemical test. No THC and CBN were detectable by GC/MS, however, trace amounts of THCA using GC/MS/MS. A comparative study of hair samples (screening for cannabinoids using ELISA test, THC determination by GC/MS, THCA by GC/MS/MS) showed that only 26 segments of 66 were positive for both THC and THCA. Thirteen were negative for THC and positive for THCA, and six were positive for THC but negative for THCA. The cases were selected by an ELISA test or re-examined when the blood/urine results or the statement of the accused did not match with a THC outcome. The most appropriate strategy to prove cannabis consumption is immunochemical initial test followed by a GC/MS/MS confirmation of THCA.

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