Quantitation of cannabinoids in biological fluids by radioimmunoassay.

A tritium based radioimmunoassay for delta9THC and its metabolites has been developed for the use of investigators studying the epidemiological, medical, clinical, and research aspects of cannabis use. The assay is sufficiently sensitive to detect cannabinoids in the urine of marijuana smokers for several days after their last exposure to the drug. The results obtained from a 28 day study indicate that the assay reflects the administration and removal of oral doses of THC. The specificity of the antisera, as determined in cross reactivity studies, allows not only the assay of metabolites in biological samples without interference from other drugs, but also the evaluation of extracts of other kinds of samples which may contain unmetabolized delta9THC. The technique of radioimmunoassay has many advantages over other methods of analysis. It is simple to perform and can be readily applied to the rapid analysis of large numbers of samples. It can be used in the direct analysis of physiological fluids and other biological samples which ordinarily have to be processed before other techniques can be applied. The method is non-destructive abd obviates the need to use radiolabelled drugs in man during metabolic and other studies. This radioimmunoassay has been designed with particular emphasis on ease of use by other investigators. We anticipate that it will prove useful to investigators and scientists for determining the absence, or presence and amount, of THC metabolite in a biological specimen, for epidemiologists in determining the full extent of cannabis use and to the medical/clinical community for establishing the minimum effective dose of delta9THC for each patient. The widespread application of a single method of analysis should also remove a great deal of the controversy surrounding marijuana studies performed to date.