MONTREAL — Despite the rapid legalization of marijuana worldwide, it’s still smart to refrain from smoking weed in adolescence. A new study finds that the earlier a person begins using marijuana, the worse the impacts.

Researchers at Concordia University reviewed a trio of studies that examined alcohol, tobacco, and drug use. One of the studies reviewed was American, while the other two were Canadian.

The researchers found that while the vast majority of marijuana consumers start before age 21, marijuana use can be particularly detrimental as a teenager — particularly for those aged 15 or younger.

A review of longitudinal studies showed that smoking weed when under 15 contributes to memory loss, cognitive impairment, diminished IQ, and lower success in school, along with a higher risk for respiratory diseases and certain cancers.

“We found that if the age of first use is below 15, it’s always bad for you,” says study co-author James McIntosh, a professor of economics in the Faculty of Arts and Science, in a university news release.

Conversely, those who waited until age 21 to try pot were found to not form a lifelong dependency, much less the same host of symptoms.

It is important to note that the negative effects seen in youths who smoked weed were prevalent almost regardless of the quantity consumed.

McIntosh et al. hope that their research sparks not only smarter legislation— i.e. laws that don’t legalize marijuana for minors— but educational programs and counseling services that would help curb marijuana’s negative effects.

Interestingly, McIntosh still advocates for pot legalization in his home country of Canada, noting that it would allow the government “to take marijuana out of criminal hands, to tax it, to make sure that product quality is preserved.”

The study was published in the journal Health.