People with schizophrenia die younger than the general population, and a large part of this excess is due to unnatural causes. When asked to pick the single commonest premature cause of death, the answer relates to self-harm rather than to violence from others or to treatment side effects.
Suicide is the leading unnatural cause, accounting for a substantial fraction of deaths, with a lifetime suicide rate of around 5 to 10 percent. The danger is greatest in the early years after diagnosis, in young men, in those with insight-related depression, and in the period immediately following hospital discharge.
By comparison, being a victim of homicide is uncommon, deaths from antipsychotic toxicity are not the dominant cause, and hospital acquired infection is a minor contributor. The expected answer is therefore self-inflicted death.
\[\boxed{\text{Suicide}}\]