Mental disorders may prevent, not cause, suicide.

We challenge a prevalent belief that depression causes suicide and propose that certain symptoms of depression and other psychopathologies may function to prevent lethal self-injury. Theoretical and empirical evidence supports this position. As suicide posed an extreme fitness hazard throughout human evolution, our species evolved special-purpose psychological defences that continuously monitor and manage this danger. Last-ditch protections may present as diverse psychiatric phenomena. Mobilising in adolescence and adulthood in response to chronic distress, these usually stop suicidal thoughts from escalating into deadly actions. The theory is testable. We point to important implications for the clinical management of suicide and psychopathology.