Identification of Non-responders to Levothyroxine Therapy

A Randomized Crossover Study, Examining Differential Effects of Levothyroxine and Liothyronine

The purpose of this study is to assess differential effects of T4 and T3 on cell and tissue level

15-20% of the patients with hypothyroidism remain symptomatic, despite adequate thyroxine substitution. Endocrinologists are split in their opinion on combination therapy with T4 and T3 on patients with poorly regulated hypothyroidism. There are no objective means, by which to identify individuals who would benefit from combination therapy. The purpose of this study is to assess differential effects of T4 and T3 on body temperature, metabolism, muscle strength and brain function. The main aim is to try to identify biomarkers reflecting different effects of T4 and T3 on cell and tissue level.

Inclusion Criteria:

• Poorly regulated hypothyroidism
• Female aged between 18 and 65 years
• Written informed consent obtained from the patient according to national regulations

Exclusion Criteria:

• Cardiovascular disease
• Chronic liver disease
• Chronic kidney disease
• Any other endocrinological disease
• Use of beta blockers
• Pregnant or lactating females
• Hormonal substitution other than T3 and T4
• Known psychiatric disease