["Clinical Psychology &Psychotherapy, Volume 33, Issue 2, March/April 2026. ", "\nABSTRACT\n\nBackground\nCognitive behavioural therapy (CBT) is an effective intervention for adults with attention‐deficit/hyperactivity disorder (ADHD). While both brief (6‐session) and standard (12‐session) formats show efficacy, it remains unclear whether treatment response differs between distinct ADHD clinical presentations.\n\n\nMethods\nThis secondary analysis of a randomized trial included 80 adults with ADHD (57.5% male; mean age = 41.26 ± 9.32 years) allocated to brief or standard CBT. Clinical and functional outcomes were assessed at baseline, posttreatment, as well as 3‐ and 6‐month follow‐ups. Linear mixed‐effects models and the Reliable Change Index (RCI) evaluated interactions between time, treatment format and ADHD presentation (inattentive vs. combined).\n\n\nResults\nCBT yielded significant improvements across all domains, with 94.5% of participants achieving reliable symptomatic improvement. A significant time × presentation interaction (p = 0.001, ηp2 = 0.135) revealed a steeper core symptom reduction in the combined group, which survived sensitivity analyses controlling for baseline severity. Regarding format, the brief version produced greater observer‐rated symptom improvement, whereas the standard format yielded greater long‐term functional gains (p = 0.009, ηp2 = 0.061). Improvements were sustained at the 6‐month follow‐up. No robust three‐way interactions emerged.\n\n\nConclusions\nCBT is highly effective and durable across ADHD presentations and formats. Although the combined presentation exhibited a more pronounced reduction in core symptoms, this differential trajectory represents a promising clinical trend requiring cautious interpretation. While brief formats efficiently address core symptoms, standard programs may better optimize long‐term functional recovery.\n\n"]