Teenage marijuana use does not lead to mental health or respiratory problems later in life, according to a new study that contradicts previous research linking mental illness in adulthood and youth pot smoking.
The study, released this week in the journal Psychology of Addictive Behaviors, followed the smoking habits of young men who were “chronic” smokers in their early teens who continued into their mid-20s and others who smoked rarely or never. The study also monitored men who smoked only as teens and others who smoked in their later teens and continued through their 20s.
The participants included white and black males, and the study factored in tobacco use. Ethnicity did not make a difference in the results, researchers said. The 408 participants came from a pool of 800 seventh-graders randomly selected from Pittsburgh public schools in the late 1980s. They formed part of the Pittsburgh Youth Study, a federal research program run by the Justice Department to examine drug use and juvenile delinquency.
On the basis of previous studies, the researchers expected to find evidence of mental illness, including depression, anxiety, psychotic symptoms or hallucinations.
“What we found was a little surprising,” lead researcher Jordan Bechtold said in a statement released Monday by the American Psychological Association, which publishes the journal. “There were no differences in any of the mental or physical health outcomes that we measured, regardless of the amount or frequency of marijuana used during adolescence.”
The findings contradict previous research on the consequences of marijuana use on mental health, especially for those already ill.
“The overwhelming consensus from mental health professionals is that marijuana is not helpful — and potentially dangerous — for people with mental illness,” the National Association on Mental Illness writes on its website. “Using marijuana can directly worsen symptoms of anxiety, depression or schizophrenia through its actions on the brain.”
A 2012 study conducted by the University of Oregon suggested that marijuana use has a permanent effect on intelligence. But experts have criticized that study for its small sample size, The Washington Post reported. Researchers at the University College London found in 2014 a stronger correlation between alcohol use — not marijuana — and lower IQ. Recent research by the National Institute on Drug Abuse shows that teenage drug use — from cigarettes to alcohol to marijuana — is down nationwide.
This week’s report comes as states relax marijuana laws or legalize the drug for recreational or medical use. Cannabis is legal to possess for recreational or medical use in the District of Columbia, Colorado, Oregon, Alaska and Washington. Medical marijuana is legal in an additional 19 states.
As support for legal cannabis grows, Congress is increasingly rethinking federal policy related to the drug. Bipartisan legislation to end the federal prohibition of medical marijuana was introduced in late July.