The immediate answer to whether you can get a hormone test while on birth control is yes, a blood sample can be drawn, but the results for reproductive hormones will be misleading. Hormonal birth control, such as combined oral contraceptives, introduces synthetic hormones that actively override the natural hormonal system. Readings for hormones like estrogen and progesterone will reflect the medication’s influence, not the body’s true underlying hormonal state. This interference means the test cannot provide an accurate picture of your endogenous hormone levels.
The Mechanism of Interference
Hormonal birth control primarily works by hijacking the Hypothalamic-Pituitary-Ovarian (HPO) axis, the body’s main system for regulating reproductive hormones. The hypothalamus and pituitary gland monitor estrogen and progesterone levels. When these levels are low, the brain signals the ovaries to start egg maturation and hormone production.
When synthetic hormones are taken, they create a sustained, high concentration that the brain interprets as sufficient, triggering a powerful negative feedback loop. This response acts as a “shut-off switch,” suppressing the release of signaling hormones, Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). Since the ovaries never receive the necessary signals, they remain dormant, preventing ovulation and the natural rise and fall of ovarian hormones.
Interpreting Specific Hormone Markers
Testing reproductive hormones while on birth control yields results that are predictably altered due to the suppression mechanism. Gonadotropins, the brain’s signaling hormones, are expected to be extremely low or near zero. Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) levels are suppressed because the combined oral contraceptive (COC) inhibits the mid-cycle LH surge needed for ovulation.
The natural sex hormones, Estradiol (E2) and Progesterone, will also show suppressed or artificially low levels. Progesterone levels will be absent or mimic the early follicular phase, confirming that ovulation has been inhibited. The synthetic estrogen in COCs stimulates the liver to produce Sex Hormone Binding Globulin (SHBG), which binds to sex hormones like testosterone. This increase in SHBG can cause total and free testosterone levels to appear significantly reduced, often by 40 to 60%, masking any underlying hyperandrogenism.
Testing for Non-Sex Hormones on Birth Control
While tests for reproductive hormones are unreliable, testing hormones from non-reproductive organs can still provide valuable diagnostic information.
Thyroid Hormones
Thyroid hormones, such as Thyroid Stimulating Hormone (TSH) and Free T4, are generally reliable indicators of thyroid function. However, the estrogen component of COCs can increase Thyroxine-Binding Globulin (TBG), a protein that binds thyroid hormones. This increase may necessitate an adjustment in thyroid medication for individuals being treated for hypothyroidism.
Adrenal Hormones
Adrenal hormones, including Cortisol and Dehydroepiandrosterone Sulfate (DHEA-S), can also be assessed, though with some caveats. Oral contraceptives elevate total cortisol levels, which can distort the body’s stress response. In some cases, a salivary or free cortisol test may be necessary to gain a more accurate reading of the biologically active hormone. While birth control can mask symptoms of Polycystic Ovary Syndrome (PCOS) by suppressing ovulation and lowering androgens, DHEA-S, which is primarily produced by the adrenal glands, may still show an elevated reading, providing a clue to underlying conditions.
Protocol for Obtaining a Baseline Hormone Reading
To obtain an accurate measurement of your body’s natural hormone function, you must first stop hormonal birth control and allow for a “washout period.” This period allows synthetic hormones to clear from your system and the HPO axis to reset its communication pathways. The recommended washout time is a minimum of three full menstrual cycles, or about three months after discontinuing the medication.
For individuals on long-acting methods, such as the contraceptive injection, the return to a natural cycle can take longer, sometimes six to twelve months. Once a natural cycle is re-established, the timing of the test becomes important to accurately assess hormone levels. For example, Follicle-Stimulating Hormone and Luteinizing Hormone are typically tested on day three of the menstrual cycle. Progesterone is tested in the mid-luteal phase, approximately seven days before the expected start of the next period. Any decision to stop hormonal birth control and undertake testing should always be coordinated with a healthcare provider to ensure a safe transition and proper diagnostic interpretation.