Canadian researchers followed 3,800 adolescents for four years, starting at about age 13, and found that marijuana use had a greater effect on their skills, memory and behavior than alcohol, BBC News reported.
The more the teens used marijuana, the worse these types of problems. And unlike alcohol, the harmful effects on the brain caused by marijuana were lasting, according to the University of Montreal study published Oct. 3 in the American Journal of Psychiatry.
"Their brains are still developing but cannabis is interfering with that," said lead author Patricia Conrod, a professor in the department of psychiatry. "They should delay their use of cannabis as long as they can."
She added that the findings highlight the importance of drug prevention programs, BBC News reported.
Among the teens in the study, 28 percent admitted to at least some marijuana use, and 75 percent said they used alcohol at least occasionally.