This hands-on study (hands on pubic hair) suggests that the hunt for illicit drug use may be more interesting than is generally known:
“Cocaine Contamination in Pubic Hair: Analysis of the Decontamination Method,” Guido Romano, Francesca Indorato, Giorgio Spadaro, Salvatore Barbera, and Nunziata Barbera, Egyptian Journal of Forensic Sciences, vol. 4, no. 4, 2014, pp. 129–136. The authors, at the University of Catania, Italy, report:
The aim of this study was to verify whether the external contamination of pubic hair with cocaine could inﬂuence the discrimination between active users and false positive subjects. The analysis was performed on in vivo and in vitro samples; the contamination was carried out by rubbing pubic hair with cocaine hydrochloride contaminated hands for three consecutive days….
Data from our studies show that all in vivo samples yielded false positives; the in vitro samples were negative only for 10 days and then yielded false positives.