An open study in 137 MS patients with symptoms not controlled satisfactorily using standard drugs was conducted with an oral cannabis extract (Sativex) to investigate long-term efficacy and safety. Participants had completed a 10-week, placebo-controlled study and were followed for an average of 434 days (range 21-814).

A total of 58 patients (42.3 percent) withdrew due to lack of efficacy (24 patients), adverse events (17), and other reasons (17). Patients reported 292 unwanted effects, of which 86 percent were mild to moderate, including oral pain (28 patients), dizziness (20), diarrhoea (17), nausea (15) and oromucosal disorder (12). Three patients had five serious adverse events (two seizures, one fall, one pneumonia, one inflammation of the bowel). Four patients had first-ever seizures.

The improvements recorded and dosage taken in the acute study remained stable. Planned, sudden interruption of cannabis administration for two weeks in 25 patients did not cause a consistent withdrawal syndrome, although 11 (46 percent) patients reported at least one withdrawal symptom (tiredness, interrupted sleep, hot and cold flushes, mood alteration, reduced appetite, emotional lability, intoxication or vivid dreams). The authors concluded that long-term use of a cannabis extract "maintains its effect in those patients who perceive initial benefit. The precise nature and rate of risks with long-term use, especially epilepsy, will require larger and longer-term studies."

(Source: Wade DT, Makela PM, House H, Bateman C, Robson P. Long-term use of a cannabis-based medicine in the treatment of spasticity and other symptoms in multiple sclerosis. Mult Scler 2006;12(5):639-45.)