--- title: "How does birth control (the pill) affect blood test results?" type: prep url: "https://www.test-well.com/prep/oral-contraceptives" factor: Oral contraceptives and estrogen aliases: - birth control pill blood test results - does the pill affect thyroid test - oral contraceptives SHBG testosterone low - estrogen cortisol test high reviewed_at: 2026-09-06 review_status: reviewed date_published: 2026-09-07 --- # How does birth control (the pill) affect blood test results? > Combined pills and other estrogen-containing contraceptives raise the liver's binding proteins, which changes many hormone results without changing the active hormone: SHBG rises (so free testosterone reads low), total T4 and total cortisol rise while free levels stay normal, and total copper and vitamin A rise. Estrogen also raises CRP, triglycerides and clotting factors and lowers AMH by up to a third. Progestin-only methods have much smaller effects. Keep taking it, and tell the clinician which method you use. ## Which results does it affect? | Marker | Direction | How long the effect lasts | What to do | Source | | --- | --- | --- | --- | --- | | SHBG | raises | While on estrogen; falls over 1–3 months after stopping | Expected; interpret testosterone with it | [Testing.com (AACC) — Sex hormone binding globulin (SHBG)](https://www.testing.com/tests/sex-hormone-binding-globulin-shbg/) | | Free testosterone, DHEA-S | lowers | While on estrogen | A low free T on the pill does not mean androgen deficiency; if testing for PCOS, results are muted | [Testing.com (AACC) — Sex hormone binding globulin (SHBG)](https://www.testing.com/tests/sex-hormone-binding-globulin-shbg/) | | Total T4, total T3 | raises | While on estrogen | Use TSH and Free T4 — free levels are not affected | [American Thyroid Association — Thyroid function tests (binding proteins, estrogen)](https://www.thyroid.org/thyroid-function-tests/) | | Total cortisol | raises | While on estrogen | A high morning cortisol on the pill is usually binding protein; a clinician may use salivary or urine cortisol instead | [Testing.com (AACC) — Cortisol](https://www.testing.com/tests/cortisol/) | | hs-CRP | raises | While on estrogen | Small but enough to shift risk category; note the method | [Testing.com (AACC) — C-reactive protein](https://www.testing.com/tests/c-reactive-protein-crp/) | | Triglycerides | raises | While on estrogen | Interpret lipids with the method in mind | [Testing.com (AACC) — Lipid panel](https://www.testing.com/tests/lipid-panel/) | | AMH | lowers | While on hormonal contraception; recovers within a few months off | For fertility planning, interpret with the method or retest after stopping | [Testing.com (AACC) — FSH / LH](https://www.testing.com/tests/follicle-stimulating-hormone-fsh/) | | FSH, LH, estradiol | lowers | Suppressed while on hormonal contraception | Cycle-day hormone testing is not meaningful on the pill or with a hormonal IUD/implant | [Testing.com (AACC) — FSH / LH](https://www.testing.com/tests/follicle-stimulating-hormone-fsh/) | | Copper, vitamin A, ferritin | raises | While on estrogen | Expected; ferritin often improves because periods are lighter | [NIH Office of Dietary Supplements — Iron fact sheet](https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/) | ## Why do total hormones change but free hormones don't? Estrogen tells the liver to make more of the proteins that carry hormones in the blood — sex hormone binding globulin, thyroxine-binding globulin, cortisol-binding globulin. Total hormone measurements count the bound portion too, so totals rise; the free, active fraction is what the body responds to and it generally stays normal. That is why TSH and Free T4 are the right thyroid tests on the pill, why a 'low free testosterone' on the pill is expected, and why an unexplained high cortisol should prompt the question 'are you on estrogen?' before any adrenal work-up. Progestin-only pills, the hormonal IUD and the implant do not carry an estrogen dose and have little effect on binding proteins, though they suppress ovulation-related hormones to varying degrees. ## Can you test for PCOS or fertility while on hormonal contraception? Combined pills suppress LH and FSH, lower androgens and reduce AMH, so a PCOS hormone evaluation done on the pill is muted and can miss the diagnosis. If the question is PCOS or ovarian reserve, most clinicians test after 4–8 weeks off hormonal contraception — using a non-hormonal method meanwhile — or interpret the result knowing it is suppressed. ## Common questions ### Should I stop birth control before a hormone test? Not on your own. For thyroid, metabolic and most routine tests there's no need. For PCOS, testosterone or fertility work-ups, a clinician may suggest a planned break of 4–8 weeks with alternative contraception — or interpret the result with the pill in mind. ### Does the pill affect thyroid tests? It raises total T4 and T3 but not TSH or Free T4, which are the tests that matter. If you're on levothyroxine, starting estrogen can increase your dose requirement — a TSH check 6–8 weeks after starting is standard. ### Why is my cortisol high on birth control? Estrogen raises cortisol-binding globulin, so total cortisol reads high while free cortisol is normal. A clinician who suspects a real problem uses a late-night salivary cortisol or 24-hour urine, which are not affected. ## Related - [Do you need to fast before a blood test — and which tests does eating affect?](https://www.test-well.com/prep/fasting) - [Does biotin affect blood test results?](https://www.test-well.com/prep/biotin) - [How does alcohol affect blood test results?](https://www.test-well.com/prep/alcohol) - [Should you exercise before a blood test?](https://www.test-well.com/prep/exercise) - [All preparation guides](https://www.test-well.com/prep) - [Lab visit guide](https://www.test-well.com/at-the-lab) ## Sources - [Testing.com (AACC) — Sex hormone binding globulin (SHBG)](https://www.testing.com/tests/sex-hormone-binding-globulin-shbg/) - [American Thyroid Association — Thyroid function tests (binding proteins, estrogen)](https://www.thyroid.org/thyroid-function-tests/) - [Testing.com (AACC) — Cortisol](https://www.testing.com/tests/cortisol/) - [Testing.com (AACC) — C-reactive protein](https://www.testing.com/tests/c-reactive-protein-crp/) - [Testing.com (AACC) — FSH / LH](https://www.testing.com/tests/follicle-stimulating-hormone-fsh/) --- Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-06. 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