Laboratory detection of marijuana use

R. H. Schwartz and R. L. Hawks

Frequent smoking of cannabis (marijuana) has been shown to be associated with a decline in social, mental, and perceptual skills and, during adolescence, with maladaptive emotional development. Urinalysis for the detection of such use can be a useful tool for the physician responsible for treatment and counseling of adolescents who develop habitual use of marijuana. Primary methods for urinalysis detection of cannabis use include the homogeneous enzyme immunoassay (EMIT) and the radioimmunoassay. These and other methods are discussed along with the issues of "false" results (both positive and negative) and the "limits of interpretation" that can be placed on a positive urine result. The pharmacokinetics and metabolism of the active constituents of cannabis are described as well as the interpretation of urinalysis results as they relate to use patterns. Guidelines are presented for the primary care physician for selecting candidates for such testing and for the use of such tests in the treatment or counseling of adolescents for whom marijuana abuse has become a psychological and social problem.