There is increasing evidence that childhood Attention-Deficit Hyperactivity Disorder (ADHD) elevates the risk of later Bipolar Spectrum Disorder (BD). However, it remains unclear whether different trajectories of ADHD symptoms confer differential risk for BD.

Data from the Avon Longitudinal Study of Parents and Children were available from 7811 children at age 8 years, 7435 at 10, 6798 at 13, and 1217 at 21–23 years. ADHD symptoms were assessed at 8, 10, and 13 years with the Development and Well-Being Assessment. Clinically significant hypomanic symptoms (CSHS) at 21–23 years were assessed using the Hypomania Symptom Checklist (HCL-32). Group trajectories of ADHD and its subtypes were estimated using latent class growth analysis. The prospective associations between different ADHD trajectories and CSHS were tested using logistic regression analysis.

Persistently high, increasing, remitting, and persistently low ADHD symptom trajectories were identified for the three ADHD-related categories. Individuals with persistently high and increasing levels of ADHD symptoms had increased odds of CSHS compared to persistently low class. Sensitivity analyses validated these results. In separate analyses, persistently high levels of hyperactivity and inattentive, and increasing levels of inattentive symptoms were also independently associated with CSHS.

Young people with a longitudinal pattern of high and increasing ADHD symptoms are at higher risk for developing CSHS in young adulthood compared to individuals with low symptom patterns. These two trajectories in childhood and adolescence may represent distinct phenotypic risk profiles for subsequently developing BD and be clinically significant targets for prevention and treatment of BD.