2. Tardive dyskinesias—

This important toxicity includes choreoathetoid movements of the muscles of the lips and buccal cavity and may be irreversible. Tardive dyskinesias tend to develop after several years of antipsychotic drug therapy but have appeared as early as 6 mo. tardive dyskinesia may be attenuated temporarily by increasing neuroleptic dosage; this suggests that tardive dyskinesia may be caused by dopamine receptor sensitization as a compensatory response to long-term dopamine-receptor blockade This makes the neuron supersensitive to the actions of dopamine, and it allows the dopaminergic input to this structure to overpower the cholinergic input, causing excess movement in the patient. Patients display involuntary movements, including bilateral and facial jaw movements and “fly-catching” motions of the tongue.