Levothyrox: more unsatisfied users since changes in formulation

Recently, at meamedica.fr, we have noticed a considerable increase in the number of experiences being shared about Levothyrox. Reason enough for us to investigate!

Why are more experiences being shared, has something changed with this medicine?

During our investigation we came across an article by the ANSM in which it was described what has been changed in this medicine and why:

  • Lactose has been replaced by mannitol and, as far as is known, mannitol has no effect on the dose of the tablets, whereas lactose does. Alongside this, lactose intolerant people have now been taken into account.
  • Citric acid has been added to the medicine which is an often-used excipient as well as functioning as a preservative to limit the degradation of levothyroxine over time.
The point of these changes is therefore to ensure that the active substance remains constant for the entirety of the shelf life and that lactose-intolerant users experience fewer symptoms.
Two bioequivalent studies were carried out and both demonstrated that the new excipients have no effect on how the drug works.

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Despite this, we have noticed an increase in the number of negative experiences that have been shared. Why is this?

The new variant of Levothyrox has been available since April, 2017 and has gradually replaced all available dosages on the market.
The first experience was shared in mid-April by someone who is lactose-intolerant. Initially the user was happy with the new version, but eventually the side effects became unacceptable enough to warrant stopping taking the medicine.
More experiences were shared from June onwards, and in an ever-increasing number.
In total, since the change to the excipients, 821 new experiences have been shared.

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Evaluation of efficacy, the number of side effects and satisfaction

People are noticeably less happy with the efficacy and the number of side effects, and the users are more often dissatisfied (Table 1):

  • Concerning the older version, almost 70% of users stated that the medicine was (very) effective, whereas the new version only has a 37.1% approval rate.
  • Almost 32% said that they experienced a lot or many side effects, whereas this has increased to nearly 80% with the new version.
  • The number of users who are now unsatisfied or even very unsatisfied has multiplied by almost 2.5 (from 32.6% to 80.0% of users).
Table 1: evaluation of efficacy, the number of side effects and satisfaction
Old version (n=132)
New version (n=821)
very effective / effective
a lot of side effects / many side effects
very unsatisfied / unsatisfied

The vast majority stated that they had experienced problems. The most common complaints were:
  • tiredness (57%),
  • headache (24%),
  • insomnia (21%),
  • weight gain (19%),
  • palpitations (13%),
  • hair loss (12%),
  • nausea (10%) and
  • depression (9%).
It is striking that these complaints correspond to complaints of a too fast or too slow thyroid, the effectiveness seems to change in that respect.
Everyone reacts differently to a change in medication: for one it works better, for the next it is worse. Bioequivalent studies therefore would not seem to be adequate enough to predict efficacy.

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