The manufacturers of a class of drugs - used for treating intestinal disorders - containing the ingredient metoclopramide, were Thursday asked by the Food and Drug Administration to add a "black box" warning about a largely irreversible movement disorder associated with long-term use of the drugs.

Metoclopramide, which has been available in the US market since 1985, is used by nearly two million Americans, as a part of treatment for GERD - gastro-esophageal reflex disorder - and for diabetic patients suffering gastroparesis, or some cancer patients undergoing chemotherapy.

The continual use of drugs containing metoclopramide causes tardive dyskinesia - a movement disorder which results in weird uncontrolled motor activities - like lip smacking, tongue protrusion, rapid eye movements and blinking, and impaired movement of the fingers and jerking of extremities.

The FDA says that since such symptoms of movement disorder are not often reversible, the maximum duration of the treatment should be three months because the inherent risk is "directly related to the length of time a patient is taking metoclopramide and the number of doses taken."

In the opinion of Dr. Karen Woodcock, director of the FDA's Center for Drug Evaluation and Research, the chronic use of the drugs - which come in the form of tablets, syrups and injections - should be avoided in all cases other than those rare ones in which "the benefit is believed to outweigh the risk