The aim of this study was to evaluate whether physical exercise or food deprivation may increase cannabinoid levels in serum or urine in abstinent chronic cannabis users. The study took place in a drug detoxification ward parallel to study participants receiving treatment. Six chronic, daily cannabis users (one female, five males, average age 30.0 years; BMI 20.8) were exposed to a 45-min. moderate-intensity workout and a 24-hr period of food deprivation. Serum samples were drawn prior to and after interventions and analysed for ∆9-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-∆9-tetrahydrocannabinol (THCCOOH) by liquid chromatography–tandem mass spectrometry (LCMSMS), and all voided urine was tested for THCCOOH by LCMSMS and normalized to the creatinine levels, yielding ng/mg ratios. There were no major differences in the measured cannabinoid levels in serum or urine before and after physical exercise or food deprivation. We conclude that exercise and/or food deprivation are unlikely to cause sufficient cannabinoid concentration changes to hamper correct interpretations in drug testing programmes.