Leading article: The cannabis debate

Our front-page headline last week, "Cannabis: an apology", certainly grabbed the attention of a lot of people. No issue since the Iraq war has provoked such a reaction from our readers and from other media. Today we publish a selection of letters, including many from people dismayed by our repudiation of our 1997 campaign to decriminalise cannabis.

Our front page was no mere attention-seeking device, however. The Independent on Sunday has changed its view because of the growing weight of evidence that cannabis contributes to mental illness. Yes, we sought to dramatise that change, not least in order to question some outdated assumptions and suggest people look again at the latest evidence.

It may be, though, that last week's headline did not do full justice to our special report. Certainly some of the journalists who contacted our office to follow up the story of our "U-turn" had not read much beyond the headline. Our "apology" was not a complete reversal of everything this newspaper stands for, or a repudiation of our fundamental liberal values. We still believe that adults should be free to live their lives as long as they cause others no harm. But the argument about the harm caused to family, friends and the wider society by cannabis-induced psychosis has changed. As we made clear in this space last week, what was a law-enforcement argument about priorities in 1997 has become, in 2007, a medical debate about mental health. Two things changed in the intervening 10 years: one was the increasing evidence that cannabis is a trigger factor in psychosis, especially for males, with the risk greater the younger cannabis use starts and the stronger the dose; the other was the big switch to high-strength "skunk".

Some of our readers doubt the medical evidence, and suggest that the growth in reporting of mental illness might have suggested causation where none exists, or even that those who are susceptible to mental illness would be more likely to misuse cannabis. We would urge them to read the testimony, on page 43, of Julie Lynn-Evans, a child psychotherapist with extensive experience in the field, which makes persuasive reading.

Others noted the Lancet study last week that compiled an "index of harm" for a number of mood-altering drugs, legal and illegal. Cannabis was ranked in the middle of the table, as more harmful than ecstasy and less harmful than either alcohol or tobacco. Two fallacious arguments are made on the basis of this kind of ranking. One is that cannabis should be legalised because more harmful drugs are already legal. That is a bit like the argument, which this newspaper never made, that we should not invade Iraq because North Korea was a worse tyranny. The other is that the risks of taking cannabis - or ecstasy - are low. There is a difference between overall "harm" and individual risk. Last week, another teenager died after taking ecstasy. And if you are among the one in four who is susceptible, to use cannabis, especially at a young age, is to take a terrible risk with your mental health.

Nor is our position the only one that has changed over the past decade. We hear much less of the "war on drugs" from the Government now, and the emphasis of public policy is much more focused on information, education and harm reduction. That is how it should be, and we should say so.