This was a review that pooled 16 studies of people who had ADHD in childhood (diagnosed before age 12) and were assessed again in adulthood (after age 18). Six studies looked back at general population groups, and ten followed patients from clinics. The studies were found by screening 26,168 abstracts. They ranged in size from 36 to 629 people, and the share whose ADHD continued into adulthood varied widely (from 11% to 79%).
Four things were each linked to higher odds that ADHD would carry on into adulthood. More severe childhood ADHD raised the odds (OR 2.33). So did having received treatment for ADHD (OR 2.09), though the authors note this may simply reflect that treated children were more severe to begin with. Having conduct disorder alongside ADHD raised the odds (OR 1.85), as did having major depression (OR 1.8).
Several other factors showed no clear link once the studies were combined: gender, family income level, IQ, oppositional defiant disorder, and living in a single-parent family.
The authors caution that the studies relied on memory or on clinic patients, that no strong long-term population study was found, and that current knowledge is not yet good enough to guide care.
Source: Caye A, Spadini A, Karam R, et al.. Predictors of persistence of ADHD into adulthood: a systematic review of the literature and meta-analysis. European Child & Adolescent Psychiatry (2016). doi:10.1007/s00787-016-0831-8