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France’s drug regulator is being investigated for issuing misleading information in connection with a thyroid treatment sold by Merck KGaA, and the move comes just weeks after an investigation was also opened into the company over the same allegation.

The probe is the latest development in a widening drama that began five years ago when thousands of patients complained about severe side effects from a new formulation of the medicine, which is called Levothyrox and is used by an estimated 3 million people in France to combat hypothyroidism. The German drug maker had phased out an earlier formulation a few months earlier.


As controversy grew, Merck explained the change was made at the request of the National Agency for Medicines and Health Products, or ANSM, and its medication was otherwise bioequivalent, which meant its effectiveness should match the original formulation. The company maintained no changes were made to the active ingredients, but did not initially publish bioequivalence results.

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