The FDA is working with the British drug giant to avoid the “rare but serious” side effect and will also update the medicine’s label to include information about the risk.

Aseptic meningitis is less serious than bacterial meningitis, but causes inflammation of the tissue layers surrounding the brain and spinal cord. Forty cases of aseptic meningitis were identified in patients taking Lamictal between since the drug was approved in December 1994, all the way up until November 2009.

During that period, more than 46m prescriptions for Lamictal were estimated to have been dispensed.

The FDA said that in 35 of the 40 cases, patients required hospitalization and in most cases symptoms ended after Lamictal was discontinued. In 15 cases, symptoms – often more severe – returned when patients restarted the drug, added the FDA.

A spokesperson for GlaxoSmithKline said that in July, the company had agreed with the FDA to add aseptic meningitis to Lamictal’s prescription information and medication guide.