Supporters and opponents of marijuana reform disagree about the effects of weed on youth, and new research seems to affirm that abstaining from cannabis during adolescence is better for your brain.

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A study in the journal Development and Psychopathology looked at cognitive assessments of about 300 self-reported marijuana users who were included in a national survey in Canada. Those who reported using the substance starting at age 14 appeared to perform worse at age 20 on memory tests (though their verbal skills were not affected) than did their nonuser peers.

The brain doesn't stop developing until a person's mid-20s, but those who started smoking cannabis at age 17 didn't show signs of any cognitive impairment, compared to their nonuser peers in adulthood.

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Natalie Castellanos Ryan, the lead author of the study, told ATTN: that "prevention efforts aiming at delaying the onset of cannabis use should be favored," based on the findings.

Castellanos Ryan added:

"We should stick to the evidence and share that evidence with young people, letting them know that, like most substances, whether, 'natural' or 'synthetic,' there are positive and negative side effects or consequences — and that even if there are some health benefits associated with cannabis, there are also some negative effects related to cannabis use, especially if you start early. To be on the safe side, it is better if youth wait until the end of adolescence before they start using it."

The researchers didn't differentiate between youth use of weed for recreational or medical purposes, and the study focused exclusively on smoked cannabis, as opposed to edibles or CBD-only products (which are non-psychoactive).

ATTN: has previously reported that components of marijuana are known to have therapeutic value for young patients suffering from epilepsy, for example.

When it comes to recreational use, the takeaway seems clear:

Cognitive functions do appear to be negatively affected by early use, and holding off until you're at least 17 seems to mitigate any cognitive problems that might arise in early adulthood.

"Although this study is one of the few prospective longitudinal studies to date that examine the link between adolescent cannabis use and its effects on cognitive functioning, it is limited in that the study did not include any measures of quantity or potency of the cannabis used, factors that will surely have an impact," Castellanos Ryan said. "Future studies should examine the quantity of use and the potency of cannabis used in order to clarify how much and what levels of THC/CBD need to be present in order to detect effects on cognitive abilities and the brain."