Hair Analysis for Drug-Facilitated Crime: The Critical Role of Hair Growth Rate

Hair analysis is increasingly used in detecting drug-facilitated crime (DFC) claiming success in identifying even single dose exposures. The calculation of accurate deposition time of the drug in hair is typically based on the assumption of mean hair growth of 1 cm/month. We describe a case of potential exposure to flunitrazepam. Assuming the literature average hair growth rate of 1 cm/month, the alleged victim had measurable amounts of the 7 amino flunitrazepam a month after the alleged drug exposure. However, in this case, due to hair dying, the true growth rate could be quantified at 1.5 cm/month. This difference has led to different interpretation from the one based on the average assumed hair growth of 1 cm/month. In conclusion, hair growth rate can be a critical variable in verifying the alleged time of drug exposure.