How bad can the side effects of haldol (haloperidol) get?

Variable: Some people have few if any side effects. Dystonic reactions with muscle rigidity and tremors are relatively common, but relieved by Cogentin or benadryl (diphenhydramine). After long term use tardive dyskinesia may occur which is uncontrolled movements of tongue, lips, and/or extremities. As with any medication it is always a matter of risk vs benefit.