By using a dominant model for COMT Val158Met, it was found that patients who were Val158 homozygotes had higher levels of depression than individuals who were Met carriers (23.7 SD 8.5 vs. 18.5 SD 8.5; independent t test, p = 0.009), while under a recessive model, Met158Met vs. Val158Val or Val158Met, no difference was found (19.3 SD 7.3 vs. 20.2 SD 9.3; independent t test, p = 0.657). Here, COMT is linked to major depressive disorder.