Smoking marijuana as a teenager lowers IQ into adulthood and could have a lifelong impact, researchers have warned.
U.S. researchers found the damaging effects of the drug remained even if users stopped smoking marijuana as adults.
They said teenagers face increased risks from smoking marijuana, because the brain is rapidly developing at this time.
The scientists, from the National Institute of Drug Abuse (NIDA) in the U.S., added that smoking cannabis affects critical thinking and memory during use, with the effects persisting for days.
Reviewing a range of studies on marijuana smoking, they reiterated that marijuana impairs driving and increases the risk of being involved in a car accident.
"It is important to alert the public that using marijuana in the teen years brings health, social, and academic risk," said lead author and NIDA director Dr. Nora D. Volkow.
The study was published in the New England Journal of Medicine.