Cannabis-based pain relief drugs could be available on prescription from the National Heath Service (NHS) within two years, the Department of Health (DoH) has announced.
Hundreds of multiple sclerosis sufferers in the UK are already being treated with cannabis-based medicines in clinical trials funded by the Medical Research Council (MRC).
Ministers are also looking at the possibility of using them for post-operative pain relief and have promised to recommend that the Medicines Control Agency licenses the treatments if the success of earlier experiments is repeated.
Now the DoH is asking the National Institute for Clinical Excellence (NICE) to investigate whether the NHS could make the drugs available on prescription.
The results of the MRC's trials are expected by the end of the year and will be used by NICE in carrying out its appraisal of the drugs.
A decision on whether any of the cannabis derivatives being tested will be licensed for official medical use is thought "likely" some time in 2004 or 2005.
The department says the NHS would need "timely and clear guidance" from NICE on the cost-effectiveness of the treatments and which patients would benefit most.
Health Minister Lord Hunt said the drugs would not made be available unless they met strict criteria.
And he denied there would be any conflict between making the drugs available on the NHS if cannabis remained illegal for recreational use.
"I think it's important to make a distinction between the drugs for MS pain relief and the use of cannabis for smoking, for pleasure," Lord Hunt said.
He added: "Of course, the Home Secretary will have to come to a view on these issues in the future, but what we're talking about here is a proper process, first for the licensing of medical products and then decisions about whether the NHS should make those products available for NHS patients."
Drug companies have isolated the active ingredients in cannabis and made them available in the form of a pill or a spray.
Neither gives a "high" - but some patients say the pills make them nauseous.
Cannabis has long been favoured by many MS and cancer sufferers for its pain-relieving properties.
They say it also stimulates their appetite without the unpleasant side effects of many alternatives currently available on prescription.
The British company GW Pharmaceuticals, which is developing cannabis-based medicines, recently said it would expand its clinical trials to look at how it could help cancer patients.