From the Research
Yes, taking oral contraceptives typically increases thyroid binding globulin (TBG) levels in the body. The most recent and highest quality study, published in 2020 1, confirms that oral contraceptives, particularly those containing estrogen, increase TBG levels. This increase is dose-dependent, with higher estrogen doses leading to greater increases in TBG. Some key points to consider include:
- The increase in TBG can occur within a few weeks of starting oral contraceptives and may persist for the duration of use.
- The elevated TBG levels usually return to normal within 2-3 months after discontinuing the contraceptives.
- While TBG levels increase, this doesn't necessarily mean thyroid function is impaired, as the body typically compensates by producing more thyroid hormones to maintain normal free hormone levels.
- However, in some cases, it may affect thyroid function test results, potentially leading to misinterpretation if not considered.
- For individuals with thyroid conditions who are taking or planning to take oral contraceptives, it's advisable to inform their healthcare provider, as thyroid function may need to be monitored more closely, and medication adjustments might be necessary in some cases. The increase in TBG occurs because estrogen stimulates the liver to produce more of this protein, which is the main carrier protein for thyroid hormones in the blood, affecting the total levels of thyroid hormones, although free hormone levels usually remain stable 1. Other studies, such as those published in 1975 2, 1992 3, 1987 4, and 1979 5, also support the finding that oral contraceptives increase TBG levels, but the 2020 study 1 provides the most recent and comprehensive evidence on this topic.