The team behind the study from the Addiction and Mental Health Group at the University of Bath, synthesised data from over 80,000 cannabis samples tested in the past 50 years from street samples collected in the USA, UK, Netherlands, France, Denmark, Italy and New Zealand. Their findings are published in the journal Addiction and the research was funded by the Society for the Study of Addiction.

The researchers investigated how concentrations of THC (the intoxicating component of cannabis responsible for giving users a ‘high’) had changed over time in different types of cannabis. In herbal cannabis, they found that THC concentrations increased by 14% from 1970 to 2017. This was primarily due to a rising market share of stronger varieties such as sinsemilla relative to traditional herbal cannabis which contains seeds and less THC.

The team have previously found consistent evidence that frequent use of cannabis with higher levels of THC carries an increased risk of problems such as addiction and psychotic disorders.

Lead author Dr Tom Freeman, Director of the Addiction and Mental Health Group at the University of Bath said: “As the strength of cannabis has increased, so too has the number of people entering treatment for cannabis use problems. More Europeans are now entering drug treatment because of cannabis than heroin or cocaine.” [Read More @ Science Daily]