A review in Britain of evidence on the drug Sativex said there were "limitations" which made it difficult to identify the place of the product in clinical practice.
Sativex, in the form of a mouth spray, contains the principal extracts -- dronabinol and cannabidiol -- found in the leaf and flower of the cannabis plant, and is the first cannabinoid preparation to be licensed for use in the treatment of muscle spasms in MS.
It is intended for use as a second-line treatment in patients in whom other options have failed.
But the review said the trial data on which the success of Sativex is based are limited.
This month's Drug and Therapeutics Bulletin (DTB), published by BMJ Journals says muscle tone, or spasticity, is a common symptom of MS, causing involuntary spasms, immobility, disturbed sleep, and pain. Complex combinations of drugs are sometimes needed to manage spasticity, but they do not work that well and have a range of unpleasant side-effects.
Overall, the trials, on which the drug's approval was based, did show a small difference in the numbers of patients in whom symptoms abated compared with those taking a dummy (placebo) preparation.
However, the makers of the drug said they believed the comments gave a misleading view and that the review writers appeared to have misunderstood important elements of trials.
GW Pharmaceuticals, the drug's maker, said: "We are disappointed with the conclusions drawn and strongly believe these comments give a misleading view of the drug."