From the FDA Drug Label
• Thyroxine concentrations may be decreased, due to a decrease in thyroid binding globulin (TBG). The use of progesterone only pill may affect thyroid function tests, specifically thyroxine concentrations may be decreased due to a decrease in thyroid binding globulin (TBG).
- This may be relevant for women with hyperthyroidism as it could potentially impact their thyroid hormone levels. However, the FDA label does not provide direct information on the use of progesterone only pill in women with hyperthyroidism. 1
From the Research
The progesterone-only pill (POP) is generally considered safe for women with hyperthyroidism, with no known interaction between POPs and thyroid function or thyroid medications like methimazole, propylthiouracil (PTU), or levothyroxine. According to the most recent and highest quality study 2, hyperthyroidism affects approximately 0.2% to 1.4% of people worldwide, and untreated hyperthyroidism can cause cardiac arrhythmias, heart failure, osteoporosis, and adverse pregnancy outcomes. The study also highlights the importance of early treatment of cardiovascular manifestations along with treatment of the hyperthyroidism to prevent significant cardiovascular events.
When considering the use of POPs in women with hyperthyroidism, it is essential to note that POPs containing only progestin (such as norethindrone 0.35mg daily, desogestrel 75mcg daily, or drospirenone 4mg daily) do not significantly impact thyroid hormone metabolism, unlike combined hormonal contraceptives containing estrogen, which can potentially affect thyroid binding globulin levels 3. Women with hyperthyroidism should take their POP at the same time each day for maximum effectiveness (within a 3-hour window for traditional POPs or 12-hour window for desogestrel).
Some symptoms of hyperthyroidism, such as irregular menstrual bleeding, may be confused with POP side effects. Regular monitoring of thyroid function should continue while using POPs, but no dose adjustments of either the contraceptive or thyroid medication are typically needed 4, 5. If a woman experiences significant changes in thyroid symptoms after starting a POP, she should consult her healthcare provider, though such effects are rare.
Key points to consider:
- No known interaction between POPs and thyroid function or thyroid medications
- POPs do not significantly impact thyroid hormone metabolism
- Regular monitoring of thyroid function is essential
- No dose adjustments of either the contraceptive or thyroid medication are typically needed
- Women with hyperthyroidism should take their POP at the same time each day for maximum effectiveness.