Cannabis treatments for multiple sclerosis may be more effective than initially estimated, according to researchers.

A review of a short-term study into the impact of drugs containing cannabinoid compounds on patients with multiple sclerosis (MS) cast doubt on whether the treatment really alleviated chronic symptoms such as muscle stiffness or spasms.

But longer term monitoring of the patients for up to a year now appears to show a greater benefit, it was announced yesterday.

Study leader Dr John Zajicek, from the Peninsular Medical School in Devon, told the British Association Festival of Science at the University of Exeter: "Initial results of the longer term study are positive and will be published in the near future.

"In the short-term study there was some evidence of cannabinoids alleviating symptoms of multiple sclerosis; in the longer term there is a suggestion of a more useful beneficial effect, which was not clear at the initial stage.

"I hope these results will encourage support of further studies of cannabinoids in multiple sclerosis and potentially other diseases."

The original 15-week study, published in the Lancet medical journal last year, showed patients found cannabinoid compounds in the drug helpful in managing chronic symptoms of MS.

But independent examinations only found some improvements in walking in mobile patients and no significant reduction in disability.

The Cannabinoids in Multiple Sclerosis Research (CAMS) study allocated MS patients capsules containing either a whole extract of cannabis, the active cannabis ingredient THC, or an inactive dummy substance.

After the initial study of 15 weeks, patients were taken off the capsules for a few days and then given the opportunity to recommence the same medication for up to a year.