WHAT links brown sugar, concrete and malaria pills? Few would answer that they were all a great way of getting high. Last month, however, all three were found in samples of illegal drugs tested at Kendal Calling, a festival in the north of England. The Loop, a charity, set up a laboratory at the event, allowing potential users to test their drugs before taking them —with an assurance that this would not lead to criminal charges. Its founder, Fiona Measham, claims that one-fifth of those who had drugs tested threw them away after discovering their true ingredients.

Festival-goers fear more than a bad trip or an overly heady buzz. Drugs in England and Wales have become more lethal of late. From 2005 to 2016, deaths from drug poisoning increased by 36%. This is despite the fact that getting high has never been less popular. During the same period, the share of 16- to 59-year-olds who reported taking narcotics in the past year fell from 11.2% to 8.5%. If fewer people are taking drugs, why are more people dying from them?

The main reason is that supply is shifting towards more potent and dangerous drugs, scaring off would-be dabblers while imperiling hard-core users. Word has spread that natural cannabis is becoming stronger, and horror stories abound about synthetic variants such as “spice”. As a result, reckons Kostas Agath of Addaction, a charity, many younger users no longer view it as harmless. The proportion of 16- to 59-year-olds who had smoked marijuana in the past year fell from 9.6% in 2005 to 6.5% in 2016. At the same time, addiction-prevention services have improved, and getting users into treatment makes them less likely to get hooked again. In 2006 11,000 people successfully completed treatment for addiction; by 2012 this figure had risen to 30,000.

Unfortunately, users who fall through the cracks in the prevention-and-treatment system face unprecedented risks. Although most discussion of the growing opioid epidemic has centered on America, this particularly dangerous class of drugs is gaining ground across the Atlantic as well. Of the 3,744 drug-poisoning deaths in England and Wales in 2016, more than half were connected to opioids—double the total from just three years ago. Increasing purity is in part to blame: even experienced users are unsure of how much to take.

Moreover, the mix of people consuming such drugs has shifted towards a more vulnerable slice of the population. Because the young have not taken to heroin as enthusiastically as the previous generation did, the average opioid user is now around 40 years old. Middle-aged people are weaker and more susceptible to overdose than young people are, particularly if they have a long history of smoking. Between 2005 and 2015, the number of heroin-related deaths among those aged 40 to 49 increased by more than 150%, while fatalities in the 50-to-69 age group quadrupled. Public-health advocates have done a good job of discouraging people from taking up illegal drugs. The data suggest that they now need to focus their efforts on a smaller group of users who face ever greater dangers.