The overwhelming majority of those who commit suicide have a mental or substance-related disorder which interferes with healthy cognitive processes and prevents them from coping normally with the stresses, strains and disappointments of life. In many cases clinical depression — a condition which is the result of a particular brain chemistry (usually low levels of serotonin) and which often has biological and genetic causes — is a determinative piece of the puzzle. Personal and family history, conflicts at home, lack of parental interest, various personality disorders, medical illnesses, and past abuse or trauma also figure significantly in the bigger picture. That's not to mention the hormonal instability, dramatic impulsiveness, immaturity, and lack of experience that are typical of many adolescents and young adults.