[Methodology and problems in the study of drugs of abuse in urine].

The analysis of drugs of abuse in urine is a valuable tool for the detection of illicit drug use and the treatment and rehabilitation of addicts. In order for the results to be conclusive, however, several precautions have to be taken during the collection, storage, mailing and analysis of the urinary specimen. Since immunological methods for the determination of drugs of abuse are not completely specific, all positive results on immunoassay should be confirmed, at least for forensic purposes, by a chromatographic technique. Although much more complicated and time-consuming, some chromatographic techniques such as gas chromatography-mass spectrometry offer the possibility of unambiguously identifying drugs of abuse. However, in some cases, even with this method it is not possible to decide whether the identified metabolite of a drug of abuse stems from food or illicit or elicit drug use. A single urinary analysis is, therefore, sometimes not sufficient to provide unambiguous proof of the use of illicit drugs. However, definite evidence of repeated drug abuse can be obtained if the person involved is carefully instructed as to which medicines or food must not be taken during the investigation period and yet the analysis of several urinary specimens taken at intervals of one or two days proves positive.