Combination thyroxine and triiodothyronine replacement therapy for hypothyroidism in adults

Combination thyroxine (T₄) and triiodothyronine (T₃) replacement therapy has been suggested as an alternative to levothyroxine monotherapy. Although improved quality of life and mood have been reported in some studies of combination therapy, the majority of studies demonstrated no significant benefit over levothyroxine monotherapy.

Available T₃ preparations (liothyronine, thyroid extracts prepared from animal tissues, and compounded preparations) contain a much higher ratio of T₃ to T₄ than is normally produced by the body. They also have short half-lives, leading to the potential for fluctuations outside the normal range of serum T₃ concentration each day, particularly if dosed once daily. Thyroid extracts and compounded formulations are not regulated by authorities for potency or consistency.

Although the available evidence cannot rule out a benefit of combination treatment in a subgroup of patients, levothyroxine monotherapy remains the treatment of choice. Combination therapy, including the interpretation of thyroid function tests during treatment, should be managed by a specialist.