Cannabinoids have analgesic and, possibly, anti-inflammatory properties but their clinical use has been restricted by legislation. This is the first United Kingdom report of the controlled use of a standardised pharmaceutical preparation of cannabinoids in capsular form. The therapy was assessed in a patient with familial Mediterranean fever, who presented with chronic relapsing pain and inflammation of gastrointestinal origin. After determining a suitable analgesic dosage, a double-blind placebo-controlled cross-over trial was conducted using 50 mg tetrahydrocannabinol daily in five doses in the active weeks and measuring effects on parameters of inflammation and pain. Although no anti-inflammatory effects of tetrahydrocannabinol were detected during the trial, a highly significant reduction (p < 0.001) in additional analgesic requirements was achieved. Future study designs can now incorporate prescribable forms of cannabinoids but the choice of previous cannabis users only as patients has clinical limitations. Cannabis naive patients would tolerate controlled investigations but may generate medicolegal problems.