IN 2000 a report published by Europe’s drug agency (EMCDDA) found that Britain had an unusually large number of young cannabis users: they “topped the EU league”, as one British paper spun it. This year’s report, published on June 4th, showed that in the past 15 years the tables have turned. While the number of 15- to 34-year-olds using pot has risen or held steady in most countries, in England and Wales it has almost halved (see chart). Why?

One possible explanation, says Alex Stevens, a professor of criminal justice at the University of Kent, is the rise in Britain of high-strength “skunk”, which is grown domestically, and the decline of cannabis resin, which is milder, and mostly brought in from north Africa. Britain’s domestic pot production is booming: the number of growing operations seized more than doubled between 2007 and 2009, overtaking the Netherlands and accounting for half the busts in Europe. But skunk’s stronger effects may put new users off: the number of Britons seeking medical help after taking pot has risen by more than half in the past ten years. The extra potency also cuts down the ways cannabis can be used. The drug is often taken alongside others, such as ecstasy; such mixing is riskier when weed’s effects are heightened.

The trend coincides with a decline in smoking. The most common way to take cannabis in Britain is still to mix it with tobacco, so non-smokers are less likely to take up the drug. In America, where cannabis tends to be smoked by itself, there seems to be no such link: the number of smokers has been falling since 2005, while that of cannabis users has risen.

Young Britons are becoming generally better-behaved than their peers: nearly all intoxicants, from alcohol to cocaine, are falling out of fashion, even as they become more popular elsewhere. British cannabis has become dearer, too. A quarter-ounce (7 grams) of skunk has risen in price from £30 in 2006 (then $55) to £50 ($77). That is about two-thirds more expensive than in Spain, for instance.

Some young people are turning to other substances. Since 2013 there has been a 25% rise in the number of new synthetic “legal highs” reported; about a third were cannabis imitators. Surveys suggest that Britons are more likely than other Europeans to buy drugs on the web, the most common way to get hold of such substances. The government has announced plans to ban legal highs, as a few other countries have already done. But driving out the online trade will prove tricky. The Home Office itself published a report in October finding no evidence of a link between stiffer penalties and rates of drug use.

Indeed, it is unlikely that the decline in cannabis use is down to anything much the government has done, or could do. Jane Mounteney at the EMCDDA notices a pattern among some large European countries: cannabis use peaks when around 20% of young adults report use in the past year, then declines. It could be that Britain got into cannabis early, and now has simply got bored with the habit.