There has been little research on the association of attention-deficit/hyperactivity disorder (ADHD) with co-occurring physical diseases. The aim of this study was to examine the association between possible ADHD and physical multimorbidity (i.e.=2 physical diseases) among adults in the English general population.

Data were analyzed from 7274 individuals aged=18 years that came from the Adult Psychiatric Morbidity Survey 2007. ADHD symptoms were assessed with the Adult Self-Report Scale (ASRS) Screener. Information was also obtained on 20 self-reported doctor/other health professional diagnosed physical health conditions present in the past 12 months. Multivariable logistic regression and mediation analyses were conducted to assess the associations.

There was a monotonic relation between the number of physical diseases and possible ADHD (ASRS score=14). Compared to those with no diseases, individuals with=5 diseases had over 3 times higher odds for possible ADHD (odds ratio [OR]: 3.30, 95% confidence interval [CI]: 2.48–4.37). This association was observed in all age groups. Stressful life events (% mediated 10.3–24.3%), disordered eating (6.8%), depression (12.8%), and anxiety (24.8%) were significant mediators in the association between possible ADHD and physical multimorbidity.

Adults that screen positive for ADHD are at an increased risk for multimorbidity and several factors are important in this association. As many adults with ADHD remain undiagnosed, the results of this study highlight the importance of detecting adult ADHD as it may confer an increased risk for poorer health outcomes, including physical multimorbidity.