The strength of street cannabis has increased across the world over the past 50 years, according to a study.
Researchers from the University of Bath synthesised data from more than 80,000 cannabis samples that had been collected from streets in the USA, UK, Netherlands, France, Denmark, Italy and New Zealand.
They found concentrations of delta-9-tetrahydrocannabinol or THC – the main psychoactive constituent of cannabis – had increased by 14% in herbal cannabis from 1970 to 2017.
In cannabis resin, which is extracted from herbal cannabis, THC concentrations rose by 24% between 1975 and 2017.
However, concentrations of cannabidiol or CBD, which is not intoxicating, did not change over time.
Dr Tom Freeman, director of the Addiction and Mental Health Group at the University of Bath, said frequent use of cannabis with higher level of THC carries an increased risk of problems such as addiction and psychotic disorders.
“As the strength of cannabis has increased, so too…