From the FDA Drug Label
5.15 Decreased Thyroxine-binding Globulin Androgens, including testosterone gel, 1. 62%, may decrease concentrations of thyroxin-binding globulins, resulting in decreased total T4 serum concentrations and increased resin uptake of T3 and T4. Free thyroid hormone concentrations remain unchanged, however, and there is no clinical evidence of thyroid dysfunction.
Testosterone supplementation in women may affect thyroid function tests, but there is no clinical evidence of thyroid dysfunction. Specifically, it may decrease concentrations of thyroxin-binding globulins, resulting in:
- Decreased total T4 serum concentrations
- Increased resin uptake of T3 and T4 However, free thyroid hormone concentrations remain unchanged 1.
From the Research
Testosterone supplementation in women can potentially affect thyroid function, and monitoring is recommended to minimize risks to morbidity, mortality, and quality of life. The relationship between testosterone and thyroid function is complex, with testosterone influencing thyroid hormone binding proteins in the blood, potentially altering the levels of free thyroid hormones available for use by the body 2. Specifically, testosterone may decrease thyroid-binding globulin (TBG), which could lead to changes in the measurement of thyroid hormones without necessarily causing clinical thyroid dysfunction.
Key Considerations
- Women using testosterone therapy should have their thyroid function monitored, particularly if they have pre-existing thyroid conditions.
- Baseline thyroid function tests (TSH, free T4, and possibly free T3) should be obtained before starting testosterone, with follow-up testing at 3-6 months and then annually if stable.
- The interaction between testosterone and thyroid function occurs because both hormone systems are interconnected through the hypothalamic-pituitary axis, and changes in one hormonal system can influence the other.
- Women may notice symptoms like fatigue, weight changes, or mood alterations that could reflect either testosterone effects or thyroid function changes, making monitoring important for optimal health outcomes.
Evidence Summary
The most recent and highest quality study on this topic is from 2019, which investigated the effect of testosterone on thyroid autoimmunity in euthyroid men with Hashimoto's thyroiditis and low testosterone levels 3. Although this study was conducted in men, it provides insight into the potential effects of testosterone on thyroid function. Other studies have also explored the safety of testosterone use in women, including its effects on lipid profiles, cardiovascular risk, and breast cancer risk 2. However, the primary concern remains the potential impact on thyroid function, emphasizing the need for careful monitoring.
Clinical Implications
In clinical practice, it is essential to prioritize the monitoring of thyroid function in women undergoing testosterone supplementation to minimize potential risks to morbidity, mortality, and quality of life. This approach ensures that any changes in thyroid function are promptly identified and managed, optimizing the overall health outcomes for these patients.