Until recently, researchers held that addiction among people with autism is rare, although there wasn’t much solid evidence for this view. It seemed plausible, though: Many people with autism have a penchant for strictly following rules, which would seem to make them less likely to try alcohol or illegal drugs. Because people with autism are often isolated from their peers, this could protect them from the peer pressure that can lead to youthful experimentation. And many people diagnosed with autism decades ago had severe features; a person who can’t live independently has few opportunities to become addicted.

A new study in Sweden, however, suggests that people with autism who have average or above-average intelligence quotients (IQs) are more than twice as likely to become addicted to alcohol or other drugs as their peers are. The risk is even higher for people who also have attention deficit hyperactivity disorder (ADHD). This study is the first to look at the general risk for addiction among people with autism.

Other research is also finding unexpected biological and psychological commonalities between the two conditions. “These two fields have really developed independently, but I think there could be a lot of cross-fertilization,” says Patrick Rothwell, assistant professor of neuroscience at the University of Minnesota Twin Cities in Minneapolis. In 2016, Rothwell opened a lab focused on studying the biological and behavioral parallels between addiction and autism.

There are similarities in the way people with either condition use repetitive behaviors to cope with emotional problems, as well as in their impulsivity and compulsions. The two conditions affect some of the same brain regions and involve some of the same genes. These connections are spurring a new area of research that could eventually help improve both autism care and addiction treatment and prevention.

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For much of the 20th century, most of those who received an autism diagnosis were on the severe end of the spectrum. In this largely nonverbal population, addiction seemed unlikely. But in 1994, when the “Diagnostic and Statistical Manual of Mental Disorders” added Asperger syndrome as a category, the spectrum extended to people who had much more opportunity to access alcohol and other drugs. Still, for years, the assumption remained that addiction was one concern the autism community could safely ignore.

When Espen Arnevik reviewed the literature for a paper he published last year, he found only 18 studies that looked at the overlap between autism and addiction. Each of them looked mainly at select samples—such as people being treated for addiction, or those caught up in the criminal justice system—rather than at the general population.

Arnevik found that the combined prevalence of alcoholism and addiction in people with autism ranged from 0.7 percent to 36 percent. Because the data were so varied, the range couldn’t be narrowed down any further. Overall, however, “most studies suggest a significantly lower prevalence than in the general population,” says Arnevik, associate professor of psychology at the University of Oslo in Norway. In the United States, the lifetime prevalence of alcoholism is 14 percent; for other substance addictions, the figure hovers around 2 to 3 percent (there is some overlap between these groups).