As marijuana use has changed over the last decade, so has the drug’s preparation. Weed 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 marijuana 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 marijuana 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 weed 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, weed potency has approximately doubled worldwide1. In the U.S., evaluation of marijuana 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.
Weedless.org is a free, web-based resource and community created by a team of healthcare professionals and researchers. We distill the facts about marijuana use and its effects into practical guidance for interested persons or for those who are thinking about or struggling to quit weed. Finding reliable, easy to understand information about marijuana should never be a struggle—that is why our core mission is to provide the most up to date information about marijuana use, abuse, addiction, and withdrawal. While we seek to empower individuals to have control over their use, we are not "anti-weed" and we support efforts to legalize adult marijuana use and study.