NEW HAVEN, Conn. (WTNH) — Recreational marijuana use is only legal for those who are at least 21 years old, but that doesn’t mean that children and youth will be using the substance.

That reality is concerning to a top Yale University cannabis researcher, who said there are links between youth cannabis use and an increase in mental health conditions and addiction.

“It’s easy for adolescents to get their hands on tobacco and alcohol and why do we think that’s not going to be the case with cannabis,” said Dr. Deepak Cyril D’Souza, the director of the Schizophrenia Neuropharmacology Research Group at Yale University.

D’Souza, who has researched cannabis for 25 years, is not opposed to cannabis or the legalization, but rather marketing that attracts young people. He’s seen the same thing play out with alcohol, cigarettes and vaping products.

Teens have chosen marijuana over alcohol in recent years.

“Exposure to cannabis has been in adolescents has been associated with the development of some serious psychiatric disorders including schizophrenia and other psychosis,” D’Souza said.

D’Souza said some recent studies have shown a connection between cannabis use and depression and suicide in teenagers. One study revealed a potential loss of IQ points, even after teens were no longer exposed to cannabis.

D’Souza said the likelihood of becoming addicted to cannabis rises the earlier the brain is exposed to it.

He advises parents and youth to wait as long as they can before trying the drug.