A study into the use of cannabis-based medicines in the treatment of multiple sclerosis (MS) sufferers has been given a £2m grant.
The long-term effects of cannabis-based medicine will be studied
The Medical Research Council-funded trial will continue research on patients by the Peninsula Medical School in Plymouth.
It suggested that THC in cannabis may protect nerve cells and help reduce muscle stiffness and disability.
The new three-year study will recruit 500 patients with progressive MS.
It is hoped that by studying patients for a longer period than the previous 18-month tests, any benefits of cannabis may become clearer.
Currently very few medicines are effective in treating MS and none have been shown to have any effect in the later stages of the disease.
John Zycheck, research leader in the Cupid (Cannabinoid Use in Progressive Inflammatory Brain Disease) project, said: "Cannabis-based medicines may have an effect on the symptoms of MS, and we've got reasonable evidence for that at the moment.
"But what we haven't got evidence for is the longer-term effect on progressive MS and we hope that some of the cannabis-based medicines may do this."