Disappearance of 6-acetylmorphine, morphine and codeine from human scalp hair after discontinuation of opiate abuse

Opiates continue to be used at high rates in East and Southeast Asia. Hair analysis for drugs of abuse has been developed into a powerful and widely used tool in forensic and clinical toxicology. Specifically, testing the proximal segment of scalp hair to confirm morphine (MOR) positive urine samples could solve the poppy seed problem. Human scalp hair grows approximately 1 cm per month and can therefore reflect a retrospective timeline of drug exposure. This study is the first to investigate the disappearance of 6-acetylmorphine (6-AM), MOR and codeine (COD) from human scalp hair after the discontinuation of drug use. Thirty-two healthy women (ages 21–51 years) with a known history of heroin abuse, who went to a rehabilitation centre and ceased consuming heroin (for 4–5 months), were recruited into the study. A pharmacokinetic analysis in seven individual hair segments was performed using a first-order kinetic. Assuming a rate of hair growth of 1 cm/month, the mean hair elimination half-lives of 6-AM, MOR and COD were 0.88 months (95% CI, 0.74–1.03), 0.73 months (95% CI, 0.64–0.81), and 0.61 months (95% CI, 0.54–0.69), respectively. Our results suggest that to evaluate the discontinuation of opiate abuse after a 6-month period of abstinence, the results from a 3-cm proximal hair segment should be free of 6-AM at the proposed 0.2 ng/mg cutoff level. This finding should become the basis for the interpretation of results from segmental hair analyses in the evaluation of drug abstinence.