Which is better for under active thyroid. Syntheroid or t3 (liothyronine)?

Synthroid (thyroxine) Synthroid or some form of levothyroxine is most commonly used. If you are taking it and are concerned that it is not working properly after several months you can ask your doctor to check T3 (liothyronine), (liothyronine) but usually with an adequate dose of T4 the body synthesizes plenty of T3 (liothyronine).