Why do I need to stay on the same brand of levothyroxine?

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Different brands of levothyroxine may be absorbed differently by your intestines. Because levothyroxine dosing needs to be precise, small differences in dose could result in over- or under-treatment.

If your brand is switched, it is recommended that you undergo TSH retesting and you may also need to have your levothyroxine dose adjusted until your TSH levels are within the normal range.

For these reasons, experts recommend that patients stay on the same levothyroxine preparation throughout treatment.