PARIS (AP) — A French association of people affected by a drug that caused birth defects has launched a class action against pharmaceutical company Sanofi.

APESAC President Marine Martin told The Associated Press that Sanofi now has four months to acknowledge its responsibility before a judge takes up the case. Sanofi has been selling the anticonvulsant drug in France since 1967.

A study revealed by Le Canard Enchaine newspaper found that the drug, Depakine, was prescribed to more than 10,000 pregnant women between 2007 and 2014. Martin says Sanofi failed to properly inform users about its potential risks for unborn children.

A study published in February estimated that around 450 children in France who were exposed to the drug while in the womb were born with congenital defects.