Marijuana packs a lot more punch than it did 50 years ago, making it a greater threat to health, researchers say.
"As the strength of cannabis has increased, so too has the number of people entering treatment for cannabis use problems," said study co-author Tom Freeman, director of the addiction and mental health group at the University of Bath in England.
In Europe, more people now enter drug treatment because of pot than heroin or cocaine, Freeman said in a university news release.
He and his team assessed how concentrations of THC (the marijuana component that causes a high) has changed over time in different types of cannabis. They analyzed data from tests on more than 80,000 street samples collected in the United States, United Kingdom, Netherlands, France, Denmark, Italy and New Zealand over the past 50 years.
THC concentrations in herbal cannabis increased by an average of 14% from 1970 to 2017, primarily due to a rise in stronger varieties, according to the authors.
They previously found that frequent use of cannabis with higher THC levels increases the risk of addiction and psychotic disorders.
The study also found particularly large THC increases in cannabis resin, with a 24% jump between 1975 and 2017. Cannabis resin is extracted from herbal cannabis and is now typically stronger than herbal cannabis, the researchers said.
"Cannabis resin -- or 'hash' -- is often seen as a safer type of cannabis, but our findings show that it is now stronger than herbal cannabis. Traditionally, cannabis resin contained much lower amounts of THC with equal quantities of CBD [cannabidiol]," said study co-author Sam Craft, also from the addiction and mental health group at the University of Bath.
"However, CBD concentrations have remained stable as THC has risen substantially, meaning it is now much more harmful than it was many years ago," he said in the release. CBD is not intoxicating and may have potential medical uses.
Marijuana -- the most widely used illicit drug in the world -- is legal in many countries and a number of U.S. states.
"As the strength of cannabis has risen, consumers are faced with limited information to help them monitor their intake and guide decisions about relative benefits and risks. The introduction of a standard unit system for cannabis -- similar to standard alcohol units -- could help people to limit their consumption and use it more safely," Freeman said.
The study was published recently in the journal Addiction.
For more on marijuana, see the U.S. National Institute on Drug Abuse.
SOURCE: University of Bath, news release, Nov. 16, 2020