Cannabis THC Levels Have Been Rising For Decades

A new study by the Society for the Study of Addiction has revealed that THC levels in cannabis plants have been rising nearly 0.29% each year for the past half-century.

As many will know, there are two major compounds within the cannabis plant that receive the most attention: THC and CBD.

THC stands for Tetrahydrocannabinol, and is the active ingredient in cannabis which causes users to get "high."

CBD, on the other hand, stands for cannabidiol and is non-psychoactive but retains many of the same medicinal properties of THC – meaning that users can enjoy its benefits such as reducing anxiety and insomnia, while aiding those who suffer from ailments such as epilepsy and Parkinson's, without getting intoxicated.

However, a recent study from the Society for the Study of Addiction, published in the journal Addiction has found that over a period of 42 years, THC levels in cannabis plants have been rising at a rate of 0.29% each year.

THC levels
Mean (standard error) concentrations of delta‐9‐tetrahydrocannabinol (THC) in all herbal cannabis over time. (Source: Wiley)

This means that cannabis increased in potency by 12.8% between 1975 and 2017 during the study period.

Moreover, when it comes to cannabis resin, which is a form of cannabis concentrate known as hashish or "hash," Tetrahydrocannabinol rates have risen even more rapidly, increasing at 0.57% each year, equating to a 22.9% increase between 1975 to 2017.

This means that for those who continue to purchase cannabis on the black market, where THC concentrations are unknown, they are consuming much more potent cannabis than that of 45 years ago.

The study was performed by analyzing 12 eligible studies that used illicit cannabis materials from the USA, UK, Netherlands, France, Denmark, Italy and New Zealand over the 42 year period, predominantly focused on the sensimilla strain.

The study concludes by stating:

"In conclusion, concentrations of THC have continued to increase in herbal cannabis and cannabis resin. Increases in THC were greatest in cannabis resin whilst increases in herbal cannabis are primarily attributable to a greater market share of high‐THC varieties such as sinsemilla. Concentrations of CBD remained stable in both herbal cannabis and cannabis resin. Increases in THC concentrations have important implications for the health effects of cannabis."

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Louis O'Neill
Louis O'Neill

Louis is a writer based in Sydney with a focus on social and political issues. Having interviewed local politicians and entrepreneurs, Louis now focuses on cannabis culture, legislation & reform.