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Methamphetamine is widely believed to cause brain damage and cognitive impairment in users. But this claim may be wildly overblown, according to a new review of the research.

In 2004, the New York Times ran a story about how meth use eats away brain cells, headlining it this way: “This Is Your Brain on Meth: A ‘Forest Fire’ of Damage.” In 2005, another Times piece about the rise in foster children taken from parents who use meth noted the “particularly potent and destructive nature” of the drug and claimed that “rehabilitation for methamphetamine often takes longer than it does for other drugs.” And the authors of a 2002 study on the brain-robbing effects of meth warned, based on their data, that the “national campaign against drugs should incorporate information about the cognitive deficits associated with methamphetamine.”

Now reviewers led by Carl Hart, associate professor of psychology at Columbia University, have examined more than 40 studies of the effects of methamphetamine, including lab research on short-term effects, brain-imaging data, and cognitive tests done on long-term meth users who had quit. (Full disclosure: Hart and I are currently writing a book together.) What they found was that the claims of meth-related harm to the brain may be as exaggerated as the hype from the ’80s and ’90s around children exposed prenatally to crack cocaine, who were foretold to end up with lifelong disabilities, or of even earlier claims that smoking pot caused insanity.

The studies on meth did find differences in both the brains and in the performance of methamphetamine users when compared to controls. And animal research has also shown that large doses of methamphetamine can cause major damage to the brain’s dopamine receptors, which are important for motivation, movement, pleasure and choice. Thus, many researchers had concluded that the drug was seriously dangerous to the brain.

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But after digging into the data as a whole, Hart and his colleagues revealed a much more hopeful picture. For one thing, he says, the lab studies on the short-term effects of meth show improvements in attention, memory, information processing and learning in users. That’s not entirely surprising considering that some forms of amphetamine (DesOxyn, for example, which is pure pharmaceutical methamphetamine) are actually approved by the government to treat ADHD, and are sometimes misused by college students seeking better grades.

Secondly, Hart found that the studies that claimed methamphetamine users were less intelligent than non-users had several typical flaws. The first was that the control groups were not always appropriately matched to the methamphetamine users. “You have to compare them with people of the same level of education and same age, because age and education are both important factors for cognitive functioning,” says Hart, explaining that in some studies, the drug users had only a high school education but were being compared with college students. Obviously, that would make the high school-educated group look worse — methamphetamine or no methamphetamine.

Moreover, even if you have the right control group, simply showing that one group does worse than another, statistically speaking, doesn’t necessarily mean that the second group is “impaired.”

“Statistical significance is just a mathematical difference,” says Hart. “When we compare, say, artists with professors, you can probably find some statistically significant differences in cognitive test performance, but no one would say that this means artists are clinically significantly different from the professors [or are impaired].”

In other words, Hart says, showing a statistically significant difference on a test is one thing, but showing a clinical difference — that is, true impairment in terms of functioning in everyday life — is something else entirely.

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What about the scary animal data showing destruction of dopamine neurons in the brain? Hart says that in these studies, rats were typically given massive doses of meth that no human user would take initially. “It’s 20 to 100 times that what humans would take,” he says, explaining that human users usually start with lower doses, and then may increase their usage over time. When rats are similarly given the drugs in this more gradual pattern, this type of brain damage is not seen.

Even the brain-imaging findings are more reassuring than they have been claimed to be. Chris-Ellyn Johanson, a neuroscientist who is now retired from Wayne State University, conducted one of the studies on this subject covered in the review. “We did find some differences between the control group and the experimental group in terms of a few cognitive functions. And we did find some differences in terms of receptors [in the brain],” she says. “But we found no relationship between the two, and the cognitive differences were within the normal range.”

That is, the differences in brain structure in meth users’ brains didn’t correlate to differences in cognitive function. Observing that people’s brain structure or receptor patterns are unusual may be interesting, but it doesn’t matter much unless those differences are also linked to specific problems. “It’s like taking the engine of a BMW and comparing it with the engine of a Mercedes,” says Hart. “The Mercedes might be bigger. But saying that means that the BMW is impaired — that’s what we’re doing with this imaging.”

The review even takes on “meth mouth,” noting that the dry mouth symptoms that have been blamed for the terrible dental problems seen in some methamphetamine users also accompany the use of legal amphetamines and some antidepressant medications. The authors write that the association between methamphetamine use and dental problems may have “less to do with pharmacological effects of methamphetamine and more to

do with non-pharmacological factors, ranging from poor dental hygiene to media sensationalism. Indeed, much of the evidence linking methamphetamine abuse and tooth

decay is anecdotal; detailed investigations of the impact of methamphetamine abuse on dental health with suitable oral health assessments are lacking.”

Of course, this doesn’t mean that illegal methamphetamine use is safe. And the types of studies included in the new review may still be helpful in terms of helping researchers learn more about the mechanisms of addiction and to better treat people with drug problems. “The hype and all that aside, there are still good reasons to do this research, and some findings may point the way to more novel pharmaceutical [treatments],” says Johanson.

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The problem is that the hype may do serious damage to those struggling with methamphetamine problems. “One of the major reasons I did the review is that one of the most effective treatments is cognitive behavioral therapy,” says Hart. “The argument has been made that these people can’t benefit because they are cognitively impaired and can’t pay attention. There’s no scientific evidence to support that position.”

Indeed, the idea that those who take methamphetamine are more likely to fail at treatment or need longer-term care than people with other addictions is not supported by the data, either. Unfortunately, by pushing the idea that methamphetamine damages the brain, researchers may inadvertently deter treatment seeking, both by making people with addictions feel hopeless and by making providers have less faith in their ability to help.

“Impaired, deficits, cognitive deterioration, decline — all those kinds of words are inappropriate,” says Hart. “There haven’t been any treatment outcome differences. I think that we have almost exclusively focused on the pathology of drug users and if you only look at pathology, that’s all you find.”

If differences aren’t reliably linked to problems, they may be useful in ultimately helping researchers learn something about the brain, but they don’t tell us anything about how to treat methamphetamine problems. Claims of cognitive impairment—and other severe problems associated with drug use—need to be made cautiously in light of their history of failure to be replicated in careful studies and their proven ability to stigmatize people.

The review was published in Neuropsychopharmacology.

Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.