A new study drawing on data from the Netherlands is the first to show how admissions to treatment centres rise and fall in line with cannabis THC strength.
The report, ‘Changes in cannabis potency and first-time admissions to drug treatment: a 16-year study in the Netherlands’ found evidence to suggest that more potent strains of cannabis have an impact on the number of people seeking help from drug treatment programmes.
Researchers at King’s College London drew on data from the Netherlands to show that admissions to specialist treatment centres rose when coffee shops sold increasingly more potent cannabis, but fell again when the cannabis weakened.
The report found that changes in demand for treatment typically lagged five to seven years behind changes to cannabis strength.
The demand for specialist treatment among cannabis users has risen steadily in recent years, with more people now citing the drug on admission than any other illicit substance. In Europe, the number of first-time referrals for cannabis rose 53% from 2006 to 2014.
Many countries have seen far stronger cannabis come on to the market in the past few decades.
Writing in the journal, Psychological Medicine, the researchers show that THC levels in cannabis increased from an average of 8.6% to 20.4% from 2000 to 2004, then slowly fell to 15.3% by 2015. When the researchers looked at the impact on drug treatment programmes, they found that first-time cannabis admissions nearly quadrupled from seven to 26 per 100,000 inhabitants from 2000 to 2010, and then dropped to less than 20 per 100,000 inhabitants in 2015. It means that for every 1% increase in THC, about 60 more people entered treatment.
Val Curran, professor of psychopharmacology at University College London, said: “This adds to a growing number of scientific studies which suggest rising THC potency of cannabis is associated with greater incidence of mental health problems including addiction and possibly psychosis.”
But she added that stronger cannabis was not solely responsible for increasing demand for drug treatment. “Other factors include the marked decrease in levels of cannabidiol (CBD) in cannabis. There is evidence that CBD can protect against some mental health harms of THC,” she said.
Ian Hamilton, a mental health lecturer at the University of York, agreed that other factors beyond the potency of the drug were important. “It is possible that seeking help for problems with cannabis has become more acceptable by users and treatment providers. Over the same period that cannabis referrals to treatment have been increasing, referrals for problems with opiates such as heroin have been in decline. So although cannabis has traditionally been viewed as relatively benign by treatment workers they may now be more inclined to offer support,” he said.