As cannabis use has changed over the last decade, so has the drug’s preparation. Cannabis has over 100 chemical constituents, known as “cannabinoids”, which alter neurotransmitter release in the brain. Two of the most active and studied cannabinoids are Δ9-tetrahydrocannabinoid (THC) and cannabidiol (CBD).
THC is the main psychoactive component of cannabis and is responsible for its intoxicating effects. Experimental studies show that THC can cause memory impairment, anxiety, and transient psychotic-like symptoms in a dose-dependent manner. Meanwhile, CBD is non-intoxicating and has been found to offset some of the harmful effects of THC, including memory impairment and psychotic-like symptoms.
The potency of cannabis is judged based on the THC content of the preparation. Additional risk may be inferred by the THC/CBD ratio. A growing body of research shows that high potency cannabis is associated with adverse health outcomes including elevated symptoms of cannabis use disorder, increased admission for specialist drug treatment, and higher risk of developing psychosis. Both absolute and relative increases in THC concentration are therefore thought to have important implications for the health of cannabis users.
Over the past four decades, cannabis potency has approximately doubled worldwide1. In the U.S., evaluation of cannabis potency from samples confiscated by the Drug Enforcement Administration showed that the average concentration of THC increased from about 4% in 1995 to 17% in 2017.
Similarly, in the U.S. and Europe, the relative concentration of THC has increased substantially in recent years. One study in the U.S. found that the ratio of THC to CBD has increased from 14 in 1995 to about 80 in 20142. These trends increase the potential harms from using cannabis.
There was a four-fold increase in the concentration of THC assayed in cannabis samples collected in 1995 and 2017.
The ratio of THC to CBD assayed in cannabis samples collected in 1995 and 2014 increased dramatically.