MAOB and post-traumatic stress disorder: In addition, significantly (Mann–Whitney test) decreased platelet MAO-B activity was also found in veterans with PTSD with more pronounced symptoms, i.e., severe depressive symptoms, compared with platelet MAO-B activity in those with mild depressive symptoms, in both smokers (U = 8964.0; p < 0.001) and nonsmokers (U = 1876.0; p = 0.007) (Figure 6).