Also known as orofacial DYSKINESIA, this is characterised by involuntary chewing and grimacing, usually the result of taking ANTIPSYCHOTIC DRUGS, particularly over a long period. It is rare in those using these drugs for less than 6 months or on a low dose. The overall risk is said to be 5 per cent per year of those treated. While it may disappear when the medication is stopped, it is often permanent.