“It’s no big deal.”

That’s what advocates for the legalization of marijuana in the U.S. would like our kids (and everyone else) to believe. But it is a big deal.

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Marijuana and alcohol use are increasingly linked to lower grades among college students, another new study has found. Not only that, but it’s well-known that college students who abuse either or both of these substances have worse graduation rates and difficulties finding and keeping a job — and that’s if they’re motivated enough to get up off the couch to go to work in the first place.

Researchers from the Olin Neuropsychiatry Research Center and Hartford Hospital in Connecticut recently looked into just how detrimental smoking marijuana can be.

“The evidence showing marijuana has adverse effects is growing … yet there is very little information being transmitted to the public,” said one researcher.

Their findings show that students who drink a lot but don’t smoke much pot tend to get lower grades during the first semester of college, but then are able to bring their GPAs back up to match those of their sober counterparts.

Unfortunately, that’s not the case for students who heavily use both marijuana and alcohol. Not only did this group start out with lower GPAs than their sober peers, they also continued to get worse grades.

“We were surprised that students who consumed fairly large quantities of alcohol alone and very little marijuana did not have a consistent decrease in GPA,” lead study author Shashwath Meda told Reuters.

While the authors acknowledged that a lack of data on final GPAs, course difficulty, and graduation rates were limitations of the study, the findings still suggest limiting or preventing the use of both substances will help students better succeed in school and in life (not to mention stay well and avoid illness!) — especially during that crucial first semester of college. Both substances can otherwise impair memory, attention, and executive function.

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“I am not at all surprised by the results of this study,” said Mary Brett, chair of Cannabis Skunk Sense (CanSS), a marijuana awareness nonprofit, in Buckinghamshire, England. “Nor by the fact that pot seems to determine what the results will be.”

Parents should be very careful about what they allow their children to use, as pot is especially damaging to the developing brain, she told LifeZette.

Related: ‘This is Not Your Father’s Marijuana’

“Because the THC in pot is fat soluble, it remains in brain cells for weeks, constantly suppressing the chemical messaging system [neurotransmitters] that allow the brain, especially the hippocampus — the learning and memory center — to function normally. Alcohol, being water-soluble, is broken down at the rate of about one unit/hour, so quickly leaves the brain. Eventually with continuing pot use, the hippocampus actually begins to shrink. It is affected throughout life.”

This latest study is “just another hammer on the nail of a coffin that keeps getting bigger” when it comes to pot as a dangerous drug, said Bertha Madras, Ph.D., of Harvard Medical School.

Related: Marijuana Doesn’t Work in the Workplace

“The evidence showing marijuana has adverse effects is growing weekly, monthly, yearly, so much more than what we used to have, and yet there is very little information that’s being transmitted to the public,” Madras told LifeZette. “That to me is one of the great failings of the media of our times. They should be informing the public. Instead, they are informing the public of their own personal impressions of the drug — possibly based on personal experience or a refusal to accept the science.”

Madras’ biggest fear is that it will take years for all of the information to really come in as to the effects of long-term marijuana use, “and in the meantime, we will have lost a generation.”

The new findings demonstrate the very real consequences of heavy alcohol and marijuana use. Educators and scientists encourage parents to have honest conversations with their kids about the risks of both early on — especially as they head off to college.