Up to 4100 children in France suffered major malformations in the womb after their mothers took a treatment against epilepsy and bipolar disorders known as valproate between 1967 and 2016, France's drug regulator says.
Valproate, which has been manufactured in France by Sanofi under the brand Depakine for epilepsy and Depakote and Depamide for bipolar disorders, is also believed to cause slow neurological development, ANSM said on Thursday.
Sanofi said it had been transparent with the authorities and that it had sought to keep doctors and patients abreast of medical information.
Parents of those affected, however, say the French state and Sanofi were too slow to warn of the side effects, after the risks to foetuses became clear by the early 1980s.
The French drug authority said it would also publish a study on neurological effects of valproate in the second half of 2017.
Valproate was approved as an anti-epileptic drug in France in 1967 and has become one of the most widely prescribed treatments worldwide given its effectiveness on adult patients.
"We are aware of the painful situations faced by families whose children have problems that may be related to their mother's treatment of anti-epileptic drugs during pregnancy," a spokesman for Sanofi said in an emailed statement.
The US Food and Drug Administration warned in 2013 that valproate should not be taken during pregnancy and a Paris prosecutor launched a preliminary investigation into the authorisation and marketing of the drug in 2015 after a group of families lodged a legal complaint.
Depakine, which lost its patent in 1998, is also prescribed in more than 100 other countries.
