Smoking cannabis has a greater impact on a teens brain than alcohol, causing lasting effects on memory and the ability to reason, an international study has found.
It's "toxic" effect on the developing brain also significantly impairs inhibitory control, which the authors say might explain why early cannabis use is a risk factor for other addictions.
To protect the young brain, the researchers at the University of Montreal have urged teenagers to delay their use of cannabis for as long as possible.
“Some of these effects are even more pronounced when (cannabis) consumption begins earlier in adolescence," said co-author and PhD student Jean-François Morin.
Researchers followed a sample of 3,826 Canadian adolescents over a period of four years to try to understand the relationship between alcohol, cannabis use and cognitive development among adolescents.
The teenagers, from 31 different Canadian schools, gave details of their drug and drinking habits once a year.
Their brain skills were also tested every year in school using computer-based cognitive tests.
In total, 28 per cent of the teenagers admitted to some kind of cannabis use, compared with 75 per cent who reported drinking alcohol at least occasionally.
Cannabis more harmful than alcohol
The study found that the brain's vulnerability to cannabis and alcohol use during adolescence was associated with generally lower performance on all cognitive domains: recall memory, perceptual reasoning, inhibition and working memory.
While drinking alcohol and taking drugs at a young age is known to cause problems with learning, attention and decision-making, this study found these problems increased as cannabis use increased.
These effects were also lasting, unlike those caused by alcohol consumption.
"Further increases in cannabis use, but not alcohol consumption, showed additional concurrent and lagged effects on cognitive functions, such as perceptual reasoning, memory recall, working memory and inhibitory control,” senior author and investigator Dr Patricia Conrod told the university's news publication.
“Of particular concern was the finding that cannabis use was associated with lasting effects on a measure of inhibitory control, which is a risk factor for other addictive behaviours, and might explain why early-onset cannabis use is a risk factor for other addictions,” added Morin.
Cannabis is thought to be the most widely used illegal drug in Australia
The National Drug Strategy Household Survey 2016 showed 35 per cent people aged 14 or older in Australia used cannabis in their lifetime (6.9 million), while 10.4 per cent has used the drug in the last 12 months.
It can be addictive and its regular use has been linked to an increased risk of developing psychotic illnesses such as schizophrenia, particularly in adolescents.
The study is published in the American Journal of Psychiatry.
