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Changes in THC and CBD concentrations in cannabis over time

Nov 27, 2020

Changes in THC and CBD concentrations in cannabis over time

A study titled “Changes in delta‐9‐tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta‐analysis” has recently been published. The researchers reviewed 12 studies from the USA, UK, Netherlands, France, Denmark, Italy and New Zealand to ascertain changes in two major components of the cannabis plant: THC (mostly responsible for the psychoactive effect) and CBD (thought to mediate the effects of THC and responsible for some of cannabis medicinal properties). The study looked at both whole-plant products and resins - concentrated extracts from the cannabis plant commonly known as hashish. 

The study found THC concentrations in herbal products have been rising by 0.29% each year from 1970 to 2017. Resin products saw an increase of 0.59% each year from 1975 - 2017. This means that the THC content in an average gram of herbal cannabis rose by around 2.9 milligrams per year, while cannabis resin saw an increase of 5.7 milligrams per gram per year. A mild cannabis intoxication is considered to be around 5mg of THC, so over time these small increases could add up to increases in harm. The study also found that CBD levels in both types of products remain largely unchanged over this time. 

Go to “Changes in delta‐9‐tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta‐analysis”