Clinical Question: Is there a benefit to adding liothyronine to levothyroxine in the treatment of primary hypothyroidism?

Setting: Outpatient (specialty)

Study Design: Randomized controlled trial (double-blinded)

Synopsis: Adding synthetic triiodothyronine (liothyronine) to levothyroxine, the current standard of treatment for primary hypothyroidism, may further improve clinical symptoms. Investigators identified 46 patients, 24 to 65 years of age, with at least a six-month history of treatment with levothyroxine alone for primary hypothyroidism. Patients were assigned randomly in a double-blind fashion (concealed allocation assignment) to receive their usual dosage of levothyroxine or combination therapy (their usual levothyroxine dosage reduced by 50 μg per day plus 7.5 μg of synthetic liothyronine twice daily) for four months. Outcomes were assessed by persons blinded to treatment group assignment. No patients were lost to follow-up.

After four months, serum thyrotropin levels remained unchanged from baseline and within the normal range in both treatment groups. Quality-of-life scores based on an approved questionnaire improved significantly in both groups, but the changes were statistically similar in each group. Neuropsychologic tests of cognitive function also were statistically similar in each group. Body weight and serum lipid levels were unchanged, and no adverse events were reported by either group. The study was large enough to have a 90 percent chance of detecting a clinically significant difference between the two groups.

Bottom Line: The treatment of primary hypothyroidism with a combination of levothyroxine plus liothyronine did not affect quality-of-life scores and cognitive function to a greater extent than use of levothyroxine alone. (Level of Evidence: 1b)