Risks of reformulation: French patients complain after Merck modifies levothyroxine pills

Thousands of patients in France have complained about adverse effects after taking a modified version of Merck’s Lévothyrox (levothyroxine).

Since the drug was reformulated last year, patients have reported problems including fatigue, memory loss, palpitations, weight gain, dizziness, and nausea, prompting 318 077 signatories to a petition demanding Merck return to the previous formulation.1

The concerns of patients have led to an emergency parliamentary inquiry and the initiation of a criminal investigation by the public prosecutor for Marseilles, while the French health minister has asked Merck to continue providing the old formulation temporarily.

Meanwhile several groups of patients are taking legal action.

“Merck intends to continue to cooperate fully . . . and will provide the investigating judges . . . with all necessary documents and information,” its spokesman Matthias Reinig told The BMJ.

The European Medicines Agency is unfazed by recent events, however. It said that the pattern of side effects is the same for both Lévothyrox versions, and that “particularly high media attention and strengthened surveillance” may have increased reporting of side effects.