EPI-PHARE has studied the consequences of switching to the new Levothyrox formula in France using data from the National Health Data System (SNDS, formerly SNIIRAM), including national reimbursement data for city care (DCIR) and hospitalization (PMSI) of all individuals covered by Health Insurance in France, regardless of the social security scheme.

This study does not show any increase in the occurrence of serious health problems (death, hospitalization, sick leave of at least 7 days) or consumption of drugs used to treat somatic symptoms such as those notified in pharmacovigilance (analgesics, corticosteroids / antihistamines, treatment of orthostatic hypotension, antimigraine, antivertiginous, antidiarrheal) in connection with the transition to the new formula of Levothyrox in France. On the other hand, it shows a clear increase in the use of ambulatory care concentrated in the period from August to October 2017 and a relative increase in the use of certain drugs such as benzodiazepines following the switch to the new formula of Levothyrox.

These results do not provide any argument in favor of a clean toxicity of the new formula of Levothyrox. They rather reflect the difficulties encountered by certain patients during the change of formula, as reported through the notifications to the pharmacovigilance system, or in the public expression of patients relating in particular to the lack of information on the change in formulation.