I was a devoted pothead for several years from the age of 16. Although nowhere near as amusing as Withnail and I (but every bit as risible), half a dozen of us schoolboys would disappear in an unsupervised cloud of smoke for holidays in North Cornwall. After two weeks of eating beefburgers and ice cream, playing stoned ping-pong and listening to Echoes by Pink Floyd, we would return to school refreshed for the rigours of A levels and competitive sport.
Thirty years on, the Ancient Mariner pothead in me would like to be able to crone, 'Didn't do us any harm, just a bit of harmless fun.' But what about the scientific evidence?
First off, in general it's clear that teenage dope smokers do tend to be more screwed up. In large surveys of teens and their parents, compared with those who had never indulged, the dopers are twice as likely to be depressed or delinquent and five times as likely to be heavy drinkers.
A study of 200 teenagers provides a more complex picture of three different types of heavy user. The first is unhappy, liable to be depressed and distant from parents or friends. The second type is antisocial, prone to stealing or violence. Both are more likely to graduate to other drugs.
But the most common heavy user is an ordinary, cheerful bod who is neither depressed nor antisocial, no more likely to move on to other drugs than light users.
This suggests it is perfectly possible to be a well-adjusted teenage pothead, as indeed my mates and I would probably have seemed. We managed to pass our exams and so forth. It also shows that heavy use of the drug does not in itself cause dysfunction.
However, heavy use among the depressed or antisocial may be a sign of disturbance. Certainly, some teens use it to medicate unhappiness. When measured after their parents' divorce, use by teenage boys increases significantly.
The most revealing study observed 100 Americans from age three to 18. Believe it or not, the best-adjusted 18-year-olds were the light users. The most disturbed were those who had never tried dope at all, or the heavy users.
Observed at five years old, both these latter groups had mothers who were relatively cold and unresponsive and focused on extracting 'performance' from their child. Abstainers had authoritarian fathers.
So, both heavy use and total abstinence are signs of disturbed early care, and the authors concluded that, at least in America, light dope use is a predictor of mental health. In my case, I was partly inspired by mild depression, partly by a terror of having to talk to girls. Being 'out of it' was preferable to feeling down or revealing my lack of chat-up lines.
The trouble with many post-60s freedoms (eg less stigma towards smoking or drinking among girls) is that the vulnerable are liable to use them self-destructively. Looking back, I have to admit that dope was not a good solution to my problems and that, without it, I might have had to confront them earlier.
