Left and right hemisphere cortical thickness was lower in medicated OCD patients (N=646) compared to controls (N=1436). Regionally, we found significantly thinner cortices in frontal, temporal, parietal and occipital regions of adult medicated OCD patients (Cohen’s d between −0.10 and −0.26; Figure 3 and Supplementary Table S8a). We did not detect significant differences in cortical thickness in unmedicated OCD patients (N=831) compared to controls (Supplementary Table S8b). Medicated OCD patients compared to unmedicated patients showed lower cortical thickness in frontal, temporal and parietal regions (Cohen’s d between −0.13 and −0.21; Supplementary Table S8c and Figure S3). Similar to the main group comparison, we found lower surface area of the left transverse temporal cortex in medicated OCD patients versus controls (Cohen’s d −0.20; Supplementary Table S9a and Figure S4). We did not detect differences in surface area in unmedicated OCD patients compared to controls and when comparing medicated and unmedicated patients directly (Supplementary Tables S9b–c).
