“…Third, a quarter of the patients who were tested positive for cannabis in urine and negative in blood denied use of drugs. In the study by Stark et al evaluating the validity of self-reported substance misuse amongst detainees in police custody, nearly one half of detainees tested positive for cannabis in urine denied use of drugs [31]. However, these authors conclude that reasonable information can be usually obtained via self-reporting in detainees [31].…”