This paper describes the application of solid-phase microextraction (SPME) to cannabis testing in hair. Fifty milligrams of hair was washed with petroleum ether, hydrolyzed with NaOH, neutralized, deuterated internal standard was added and directly submitted to SPME. The SPME was analyzed by GC-MS. The limit of detection was 0.1 ng/mg for cannabinol (CBN) and delta9-tetrahydrocannabinol (THC) and 0.2 ng/mg for cannabidiol (CBD). THC was detected in a range spanning from 0.1 to 0.7 ng/mg. CBD concentrations ranged from 0.7 to 14.1 ng/mg, and CBN concentrations ranged from 0.4 to 0.7 ng/mg. The effectiveness of different decontamination procedures was also studied on passively contaminated hair. The proposed method is also suitable for the analysis of methadone in hair; cocaine and cocaethylene can be detected in hair with SPME extraction after enzymatic hydrolysis.