The idea that young adults, particularly women, actually have ADHD routinely evokes skepticism. As a fairly driven adult female who had found the strength to sit through biology lectures and avoid major academic or social failures, I, too, was initially perplexed by my diagnosis. My peers were also confused, and rather certain my psychiatrist was misguided. “Of course you don’t have ADHD. You’re smart,” a friend told me, definitively, before switching to the far more compelling topic: medication. “So are you going to take Adderall and become super skinny?” “Are you going to sell it?” “Are you going to snort it?”

The answer to all of those questions was no. I would be taking Concerta, a relative of Ritalin. Dr. Ellen Littman, author of Understanding Girls with ADHD, has studied high IQ adults and adolescents with the disorder for more than 25 years. She attributes the under-diagnosis of girls and women—estimated to be around 4 million who are not diagnosed, or half to three-quarters of all women with ADHD—and the misunderstandings that have ensued about the disorder as it manifests in females, to the early clinical studies of ADHD in the 1970s. “These studies were based on really hyperactive young white boys who were taken to clinics,” Littman says. “The diagnostic criteria were developed based on those studies. As a result, those criteria over-represent the symptoms you see in young boys, making it difficult for girls to be diagnosed unless they behave like hyperactive boys.”

ADHD does not look the same in boys and girls. Women with the disorder tend to be less hyperactive and impulsive, more disorganized, scattered, forgetful, and introverted. “They’ve alternately been anxious or depressed for years,” Littman says. “It’s this sense of not being able to hold everything together.”

Further, while a decrease in symptoms at puberty is common for boys, the opposite is true for girls, whose symptoms intensify as estrogen increases in their system, thus complicating the general perception that ADHD is resolved by puberty. One of the criteria for ADHD long held by the Diagnostic and Statistical Manual, published by the American Psychiatric Association, is that symptoms appear by age 7. While this age is expected to change to 12 in the new DSM-V, symptoms may not emerge until college for many girls, when the organizing structure of home life—parents, rules, chores, and daily, mandatory school—is eliminated, and as estrogen levels increase. “Symptoms may still be present in these girls early on,” says Dr. Pat Quinn, cofounder of The National Center for Girls and Women with ADHD. “They just might not affect functioning until a girl is older.” Even if girls do outwardly express symptoms, they are less likely to receive diagnoses. A 2009 study conducted by at The University of Queenland found that girls displaying ADHD symptoms are less likely to be referred for mental health services.