A randomized obesity pilot did not demonstrate a treatment-specific improvement in executive-function ratings or stop-signal performance over time. A difference in weight outcome did not establish the proposed cognitive mechanism.
Poulton and colleagues randomized 52 participants with body-mass indices of 25–60 to dexamphetamine titration or placebo. Participants completed a brief executive-function questionnaire and a stop-signal task repeatedly across baseline, titration, maintenance and follow-up. The experiment addressed treatment in an overweight/obesity population, not an ADHD trial or a methamphetamine dependence study.
The questionnaire showed no significant treatment-group effect or group-by-session interaction. Stop-signal reaction time showed group and session effects, but its group-by-session interaction was nonsignificant (p = 0.707). Baseline stopping times were longer than later observations across the sample. A main effect of group does not demonstrate treatment-induced change when the expected differential time course is absent. Repeated testing and sample variation therefore remain plausible contributors.
The pilot was small and assessed a limited set of executive outcomes. Participants may not have had the same baseline deficits as an ADHD population, so importing an ADHD mechanism would require additional evidence. Conversely, null cognitive findings do not establish that the medication is free of dependence risk; developing a substance use disorder was not validated by these cognitive endpoints. The appropriate conclusion is that the study did not demonstrate its proposed treatment-specific executive benefit. Weight change, reported functioning, inhibitory performance and long-term safety are separate outcomes requiring their own measurements.
See why findings from one clinical population do not automatically transfer.