A medical journal said that there is no strong evidence for the efficacy of a cannabis-based drug used in Britain to treat muscle spasms in multiple sclerosis (MS) patients.
The drug's developer dismissed the claims, which add to debate about the usefulness of the popular recreational drug and its extracts in treating the debilitating disease.
According to the BMJ Group journal Drug and Therapeutics Bulletin, clinical trials conducted with the drug Sativex were flawed, often lasting only a few weeks at a time and lacking data on its long-term effects.
"If you look at the evidence from the trials, it is very meagre," editor James Cave told AFP of the "disappointing" outcome of the journal's review of several Sativex trials.
"The results have been pretty poor really. In fact we were wondering quite why this drug managed to get a licence given the strength of the evidence for it."
The criticism was rejected by CW Pharmaceuticals, which said the article contained numerous errors.
"The writers appear to have misunderstood important elements of the design of Sativex clinical trials and provide a flawed assessment of Sativex data," the company's research and development director Stephen Wright said in an emailed response.
A 2008 study by the World Health Organisation and the Multiple Sclerosis International Federation reported some 1.3 million MS cases around the world, about 630,000 of them in Europe and 520,000 in the Americas.
MS affects vision, movement, balance, sensation, bladder control and eventually also memory and thinking. There is no cure.
The disease also causes uncontrollable muscle spasms, which Sativex is meant to ease.
The drug, in the form of a mouth spray, contains the extracts dronabinol and cannabidiol found in the leaf and flower of the cannabis plant, and is authorised in Britain, Spain, Germany, Denmark, the Czech Republic, Sweden, New Zealand and Canada.
The journal said two of the trials analysed exceeded the recommended daily dose of 12 sprays, and one did not have enough participants to validate the results.
A third trial, which was properly designed and had enough participants, did not find a significant improvement in symptom relief.
The drug cost about 10 times as much as others used to treat MS muscle spasms, it added.
"The strength of the evidence is insufficient to warrant its routine use," said a BMJ statement.
But GW Pharmaceuticals rejected these claims and stressed the trials had met all the specifications required by 22 authorities in Europe and around the world that had licensed the drug for use.
In October, a study published in the BMJ sister Journal of Neurology, Neurosurgery and Psychiatry said an unrelated trial had shown a tablet containing the cannabis extract tetrahydrocannabinol to ease painful muscle stiffness caused by MS.
Some MS sufferers smoke cannabis to alleviate their symptoms.