Certain drugs that are prescribed for treating stomach disorders need strong warnings regarding the risk of involuntary, repetitive movement on several parts of the body seen with long-term use or high doses

The concerned drugs contain the ingredient metoclopramide and are available in various forms including tablets, syrups and injections.

According to the FDA, more than 2 million Americans use these medicines to treat gastroesophageal reflux disease and other stomach ailments.

Long term use of the drugs has been known to cause tardive dyskinesia, which causes repetitive movements of the limbs, lip smacking, grimacing, tongue protrusion and rapid eye movements and blinking.

The FDA has recommended that a "black box" warning, the strongest available, and develop a patient-friendly guide explaining the risk must be added by the manufacturers on the labels of the drugs. It has also instructed that the drugs should not be prescribed for more than three months time at a stretch.

"The chronic use of metoclopramide therapy should be avoided in all but rare cases where the benefit is believed to outweigh the risk," Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, said in a statement.