So medical marijuana will soon be added to your local GP's prescription slate. But don't all go rushing down asking for a couple of spliffs every time you've got a stomach ache.

The drug will be available for therapeutic purposes only, initially for treatment of spacisity in Multiple Sclerosis.

However, it has clinical applications for an array of ailments, including seizures and to improve cancer patients' tolerance for treatments such as chemotherapy.

The pro-legalisation lobby might be forgiven for treating this as a small victory. But we'd be wrong to see this as an ideological step towards a more liberal era.

In amongst the minefield of drugs legislation debate and the extreme emotions it inevitably provokes, this is one area in which sane empirical evidence can prevail.

There will be many people celebrating this development. The case for legalising medical cannabis has, thank God, nothing really to do with the wider war on drugs, nor is it about gratifying the liberal values of the post-dinner party spliff-smoking set, whose support of legalising pot is as much an identity issue as an ideological one.

Instead it's simple pragmatism. Medical cannabis has been evaluated according to the same method by which we test the benefits and efficacy of any other new medicine.

An empirical cost/benefit calculation has been made and it has been deemed useful.

I have an aunt with MS, who has for years, been declaring her interest in testing out medical cannabis. For her, it's not about declaring a liberal, live-and-let-live political agenda.

She's simply a person grasping at any opportunity for some measure of reprieve from the daily struggles her condition entails.

The case in support of therapeutic cannabis is overwhelmingly strong.

Last week, the well-known academic and physician Dr Sanjay Gupta wrote a long, heartfelt public apology, renouncing his former scepticism about the benefits of the drug, and endorsing it for a range of conditions.

This idea isn't new. Before weed was herbal rebellion, it was widely used as a remedy.

It was the great counter-cultural wave of the Sixties that led to its classification as a schedule 1 drug in America. Before then, it was available on prescription.

How we make the distinction between those drugs considered recreational and those considered therapeutic is almost scarily arbitrary.

The chemical difference between heroin, scourge of the streets and most destructive of social ills, and morphine, the widely used painkiller, is pretty slight.

Indeed, heroin itself is a legally prescribed drug in the UK, often administered in place of morphine because it causes fewer side-effects.

Of course, this doesn't apply to all addictive drugs. Some are just rotten. There is, as far as I'm aware, no current constructive application for, say, crystal meth.

But the division of psychoactive substances into those that are harmful and those that are beneficial is rarely that cut and dried.

The example of legislating for cannabis use as a therapeutic drug might be instructive. If we approach recreational drugs in the same way we treat prescription ones, we might be in a better state.

Sure, there are plenty of people who abuse prescription drugs. But the vast majority of us take them sensibly, in carefully limited and regulated doses, with the aim of achieving exactly the desired effect; no more and no less.

And yet, when it comes to alcohol, or ecstasy, or cocaine, the approach of those of us who take them seems to be to neck them with impunity and hope for the best. Cannabis can do many positive things.

But like many drugs, it has significant and sometime serious side-effects. Growing evidence links its prolonged use to psychosis. Those who have to take it for medical reasons, will no doubt do so with caution and care and with attention to proper dosing in order to limit any possible harm.

Perhaps those who do it just for fun should aspire to do the same?

Sunday Independent