medication use or to symptom improvement. In contrast to these normalizing effects of SRIs, the previous univariate meta-analyses and mega-analyses of the ENIGMA-OCD study found significantly thinner cortices in medicated adult OCD patients and smaller cortical surface area in medicated pediatric OCD patients, but could not detect significant differences in cortical and subcortical gray matter between unmedicated OCD patients and HC, with the exception of larger thalamic volumes in unmedicated pediatric OCD patients6,7. Together, these cross-sectional studies suggest that medication use alters brain structure rather than necessarily normalizing it to the level of healthy individuals, an hypothesis which needs to be assessed in appropriately powered longitudinal studies.
