Marijuana is linked to several significant adverse health effects, and can be addictive, National Institute on Drug Abuse Director Dr. Nora Volkow writes in this week’s New England Journal of Medicine.

The drug can disrupt the brain function and learning of young users, she said. Marijuana has been proven to contribute to fatal motor-vehicle crashes, Dr. Volkow noted. She argued legalizing marijuana will lead to nationwide health problems similar to those seen with alcohol and tobacco, HealthDay reports.

“By making marijuana legal, you have more widespread use and many more health implications,” Dr. Volkow said. “We don’t need a third legal drug. We already have enough problems with the two we have.”

She noted 9 percent of people who try marijuana will become addicted. In young people under 18, the addiction rate is 17 percent, she wrote. “This is something that a lot of people who are pro-marijuana deny. The evidence shows otherwise.” She added people intoxicated by marijuana are three to seven times more likely to cause a motor vehicle accident than someone who is sober.

Frequent marijuana use by teens has been linked to lower IQ and a higher risk of dropping out of school, she noted. Other research has shown marijuana can impair school performance, worsen mental illness such as schizophrenia, and increase the risk of health problems such as heart disease and chronic bronchitis, she wrote.

“It is important to alert the public that using marijuana in the teen years brings health, social, and academic risk,” Dr. Nora Volkow said in a news release. “Physicians in particular can play a role in conveying to families that early marijuana use can interfere with crucial social and developmental milestones and can impair cognitive development.”