What are the worst side effects of risperidal (risperidone)?

The worst...: You could get nms which is a high fever, stiffness, confusion and possibly death, it is rare, tardive dyskinesia which is involuntary movements, rare but possibly permenent, rarely fatal. Diabetes with ketoacidosis, which can be fatal, very very rarely a pituitary tumor, rarely very low white blood cells, very rarely worse mania or psychosis. These are very rare side effects.