In this feasibility study of an observational nature, we used the protocol 'AnalyTox-Op' to compare analytical data with anamnestic reports gathered from specialized drug addiction treatment centers. These data were collected from 32 drug addicts who were patients undergoing treatment with addictive drug substitutes or prescribed psychotropic drugs. Urine toxicology screens were performed using immunological methods followed by confirmation with more specific techniques, i.e. gas chromatography coupled with mass spectrometry (GC-MS) and liquid chromatography with diode array detection (HPLC-DB). While complete agreement between patient reports of drug consumption (obtained from a questionnaire) and analytical data was only observed in 13 out of the 32 cases, a very good concordance was seen with opiate substitutes (88% with methadone and high-dosage buprenorphine, combined) and legally prescribed psychotropic drugs. Of note, however, was the omission of illicit drug use in patient questionnaires, especially with cocaine (22%) and recreational opiates (22%), causing discordance in the comparison. This study is currently being expanded to include a large number of participants across the country with the aim of obtaining data under homogeneous conditions, verifying the discordance we found and determining its significance.