Simulation of drug use and urine screening patterns.

Urine drug screens are used extensively in substance-abuse treatment, especially methadone maintenance treatment programs, as well as criminal-justice and clinical research settings. While positive urinalysis generally indicates drug use, no information is provided about the context or pattern of use. A computer generated model was created to examine the influence of drug use patterns and drug screen schedules upon urine test results. The results indicate that (1) when urine testing is performed at a rate of eight times per year, the probability of testing positive in a given month is little better than 50-50 even for daily use, (2) infrequent drug use is difficult to detect regardless of drug testing frequency, and (3) the benefits of more frequent drug testing are greatest with moderate drug use. The data presented provide a guide for clinicians to match drug screen schedules to frequency or pattern of suspected drug use.