There’s at least one scene in every teen movie where comedic hijinks follow a montage of teenagers binge-drinking. In these cinematic instances, art really does mirror life: American teenagers and young adults, regardless of what the law dictates in terms of legal drinking ages, have been getting sloppy drunk for eons. In fact, the CDC reports that more than 90 percent of alcoholic drinks consumed by people between the ages of 12 and 20 are guzzled during binge-drinking sessions. We already know there are lots of immediate dangers that can result from kids abusing America’s most popular legal drug, but it turns out there are long-term consequences, too.

A study from Duke University finds that the still-developing brains of adolescents who periodically binge-drink are negatively affected well into adulthood, a major social health risk that gets little attention compared to the potential harms associated with teenage cannabis use. To understand precisely what happens to grownup former teen drinkers, researchers got some lab rats drunk. Or rather, in their words, they “periodically exposed young rodents to a level of alcohol during adolescence that, in humans, would result in impairment, but not sedation.” They got the rats tipsy enough to lose coordination and likely some other functions, but not enough that they passed out. This process continued only during the lab rats’ adolescence. (The study indicates the pattern of administration was “2 days on, 1 day off, 2 days on, and 2 days off…for 16 days.”) Later on, the manufactured drinking sessions ceased and the rats were given no more alcohol while they reached adulthood, roughly 24 to 29 days.

What researchers discovered is that lasting damage was done to the hippocampus, “where memory and learning are controlled,” even though the binge drinking ended before maturation. At the cellular level, researchers examined “long-term potentiation (LTP),” a mechanism for “the strengthening of brain synapses as they are used to learn new tasks or conjure memories.” The scientists had hypothesized that LTP would be stunted in the adult rats. They were surprised to learn that the process was, instead, “hyperactive” in the formerly boozy rats.

“At first blush, you would think the animals would be smarter,” Scott Swartzwelder, one of the lead researchers, reported in a press release on the findings. “But that’s the opposite of what we found. And it actually does make sense, because if you produce too much LTP in one of these circuits, there is a period of time where you can’t produce any more. The circuit is saturated, and the animal stops learning. For learning to be efficient, your brain needs a delicate balance of excitation and inhibition—too much in either direction and the circuits do not work optimally.”

Without getting into too much detail, the brains of the rats exposed to alcohol in their youth developed abnormally, so that in adulthood, their brains looked immature—a neurological change that was reflected in their behavior. Melissa Healy, writing in the Los Angeles Times, explains how having a young-seeming brain, in this context, isn’t such a good thing.

The findings of the Duke study offer yet another example of the ways drinking does harm to young brains, in contrast with recent surveys finding marijuana poses little threat to teen neurology. A 2012 study conducted by the University of California San Diego and the University of Pittsburgh Medical Center found that after a year and a half, “kids who drank five or more alcoholic beverages twice a week had lost white brain matter…mean[ing] that they could have impaired memory, attention, and decision-making into adulthood.” The pot-smoking kids in the study suffered no such loss. More recently, two 2015 studies — one of which was the largest of its kind ever — found “no evidence for the causal influence of cannabis exposure” on teen brain damage, and debunks long-standing claims about teen marijuana use and the development of schizophrenia.

“[T]hey weren't immature in a stronger, faster, more youthful way,” Healy writes, “they were immature in a way that suggested they might never likely settle down and function in ways that allow learning to proceed and memories to be built, stored and maintained efficiently.”

Yikes.

Lead researcher Mary-Louise Risher says that the study shows hard partying as a teen likely alters the normal neurological path to adulthood, resulting in a brain with permanent damage.

“It’s quite possible that alcohol disrupts the maturation process, which can affect these cognitive functions later on,” Risher says. “That’s something we are eager to explore in ongoing studies.”

That’s not great news for teens who drink, of which there are plenty. The CDC’s 2013 Youth Risk Behavior Study found among the high school students polled, over just the 30 days prior to the study, 35 percent reported they’d consumed at least some alcohol, and 21 percent copped to binge drinking. More frightening is the fact that 10 percent got behind the wheel after drinking, and 22 percent were passengers in a car driven by someone who had consumed alcohol. That might explain why in 2010, there were an estimated 189,000 alcohol-related emergency room visits by young adults under the age of 21. Risher suggests that this latest finding shows that while alcohol may not always have visible and instant consequences, teens should know there could be problems down the road.

“In the eyes of the law, once people reach the age of 18, they are considered adult, but the brain continues to mature and refine all the way into the mid-20s,” Risher says. “It’s important for young people to know that when they drink heavily during this period of development, there could be changes occurring that have a lasting impact on memory and other cognitive functions.”