Leukopenia and agranulocytosis are rare, but potentially fatal, and occur in the first few weeks of treatment. The incidence of leukopenia (usually reversible) is less than 1 in 10 000 for most antipsychotics, but much higher (1-2%) with clozapine, use of which, therefore, requires regular monitoring of blood cell counts. Provided the drug is stopped at the first sign of leukopenia or anemia, the effect is reversible. Olanzapine appears to be free of this disadvantage.

Urticarial skin reactions are common but usually mild. Excessive sensitivity to ultraviolet light may also occur.