Right of Reply

The former professor of addiction behaviour at the Institute of Psychiatry in London responds to yesterday's article by our health editor on cannabis use

I WAS very interested to read Jeremy Laurance's article ("My drugs shame") including his confessions that he "inhaled, cooked, drank and ate" Afghani, Moroccan and Lebanese variants of cannabis and that "yeah, man it was groovy". But I was much more concerned about Jeremy saying that the damage caused by cannabis was "not excessive" when compared to that wreaked by smoking and drinking alcohol.

The problem is that making general comparison about different drugs can be rather fatuous. Drugs affect different people in different ways, of course. More to the point, research is not standing still and we are finding out more and more about what these substances can do to us.

As for cannabis, clearly it is the case that the majority of users will not experience serious health and social problems: 40 per cent of the population is thought to have used the drug at some time.

But there are cases where it can become addictive if used in sufficiently high doses and with regularity. In other words, there are people who want to stop using cannabis but cannot do so. Why does this matter? Well there is growing scientific evidence that suggests that the use of cannabis can lead to a number of problems. It can damage the respiratory system - with bronchitis and chest disease a danger. As with the smoking of tobacco, it seems reasonable to suggest that there may also be a link between smoking cannabis and lung cancer. And there is also evidence that cannabis use, even at so-called "social levels" can lead to the impairment of certain brain functions. This damage can be long-term.

Naive users of cannabis have also be known to experience acute psychotic or manic reactions which can last for up to 24 hours. Too many people think that cannabis is entirely harmless; it is not.