Cannabis resin has become almost 25% stronger over past 50 years, study finds

THC has increased in both cannabis leaf and resin. Picture: PA

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.