how-to
7 Medications That Can Skew Your Hormone Test Results
Iris Crawford
12 min read
Last Updated: November 5, 2026
Quick Summary
Many medicines, supplements, and high-dose vitamins can change hormone test accuracy by interfering with lab assays or by altering how your body makes and carries hormones. Biotin is one of the most common culprits, and prescription drugs like levothyroxine and steroids can shift readings in ways that look like a problem but are expected. Always share your full medication and supplement list with the team reading your results.
Biotin can cause falsely high or low results on thyroid and some hormone tests.
Levothyroxine can lower TSH as the dose rises, which is often the intended effect.
Corticosteroids can suppress cortisol and ACTH, so timing relative to the draw matters.
Tell your lab about high-dose biotin before any blood draw.
Never stop a prescription on your own before testing; ask your clinician first.
If you take a prescription, an over-the-counter remedy, or a daily supplement, your hormone test accuracy may not reflect the full picture. Many medicines and supplements can shift lab readings, sometimes enough to make a result look high or low when your body is actually fine. This guide breaks down how that interference happens and what you can do about it. Keep reading to learn which substances to watch for and how to prepare for an accurate panel.
Why Medications Can Change What a Hormone Test Shows
Hormone tests measure substances in your blood, urine, or saliva using chemical reactions called assays. Some medicines interact with those reactions, and others change the hormone levels themselves. Both can skew a result, and the two effects are very different.
Lab interference happens inside the test tube. The substance you took gets in the way of how the assay detects a hormone, so the reading is off even though your body's hormone level hasn't changed. A FDA guidance on laboratory test interference notes that drugs and other substances can interfere with laboratory assays this way.
Physiological effects are different. Here, the medicine actually changes how your body makes, carries, or clears a hormone. Estrogen-containing medicines, for example, raise the binding proteins that carry thyroid hormone, which can change what a total thyroid level looks like.
Assay interference versus a real physiological effect
Knowing which type you're dealing with matters because the fix is different:
Assay interference: Often resolved by using a different test method or a lab that is aware of the issue.
Physiological effect: Usually means the medicine is doing what it should, and your clinician needs to factor it into the interpretation.
A common mistake is assuming every odd result is interference. Many are real effects. That is why your full medication and supplement history should always go to the team reading your labs.
Which Lab Tests Does Biotin Interfere With?
Biotin, also called vitamin B7, is one of the most common causes of false lab results. It is sold in hair, skin, and nail supplements, and many multivitamins contain it at high doses.
Biotin can interfere with immunoassays that use biotin-streptavidin binding, which lowers hormone test accuracy for several common panels. The most frequently affected tests include:
Thyroid tests such as TSH, free T4, and free T3
Some hormone tests, including certain testosterone, estradiol, and cortisol assays
Troponin and other cardiac markers
The direction of the error can vary. Some assays read falsely high, while others read falsely low. A thyroid result that looks like hyperthyroidism when you feel fine is a classic warning sign.
Watch out: A biotin-driven thyroid result can look alarming enough to prompt unnecessary treatment decisions. Always tell your lab about high-dose biotin before any draw.
What Supplements Interfere With Blood Tests?
Biotin is not the only supplement that matters. Several others can affect labs or the hormones being measured:
High-dose vitamin C: Can interfere with some chemistry tests and certain urine assays.
Iron: Can change iron, ferritin, and related markers.
Herbal products: Ingredients such as licorice root can alter cortisol and aldosterone-related results.
Soy isoflavones and DHEA: Can shift estrogen and androgen measurements.
Supplements are not regulated like prescription drugs, so the dose on the label may not match what is in the bottle. Bring every product, including the label, to your appointment.
Medications That Affect Thyroid and Other Hormone Tests
Prescription medicines are among the most important factors to review before a panel, and the effect is rarely uniform. For a closer look at how hormone-related therapy and metabolic health are evaluated together, read how to tell if HRT supports your metabolic health. The same drug can push one marker up, pull another down, and leave a third untouched.
Medicine or class | Hormone tests most often affected | Likely direction | Practical next step |
|---|---|---|---|
Levothyroxine | TSH, free T4, total T4 | TSH falls as dose rises; timing of the last dose shifts free T4 | Tell the lab the dose and the time of your last pill; do not skip a dose without clinician guidance |
Estrogen therapy, oral contraceptives | Total T4, total T3, thyroid-binding globulin, sex hormone-binding globulin | Total thyroid hormones rise via binding proteins; free levels may stay stable | Ask whether free rather than total thyroid markers are the better read |
Glucocorticoids (prednisone, dexamethasone) | Cortisol, ACTH, glucose, some sex hormones | Cortisol and ACTH are suppressed; glucose rises | Report the dose and how recently it was taken; timing relative to the draw matters |
Lithium | TSH, free T4 | TSH can drift up over time; thyroid function can change | Long-term use warrants periodic thyroid review, not just a single draw |
Proton pump inhibitors | TSH indirectly via absorption; vitamin B12, ferritin | Thyroid medication absorption can fall; nutrient markers can drop | Mention long-term use so nutrient and thyroid results are read together |
Some antidepressants (SSRIs, tricyclics) | Prolactin, TSH | Prolactin can rise; thyroid readings can shift | Include the drug name and duration, not just the class |
Opioids | Testosterone, cortisol, LH | Testosterone and cortisol can fall; LH can be suppressed | Report chronic use, since the effect builds over time |
Dopamine agonists and antagonists | Prolactin | Agonists lower prolactin; antagonists raise it | Note the drug and the interval since the last dose |
Ketoconazole and other azoles | Testosterone, cortisol | Androgen and cortisol synthesis can be reduced | Flag the drug so results are not read as a standalone endocrine finding |
Metformin | Vitamin B12, TSH indirectly | B12 can fall with long-term use; thyroid readings can shift | Pair the result with B12 and a medication timeline |
The key point is that you should never stop or change a prescription on your own before a lab draw. Reporting a medication and stopping a medication are two different actions. Ask your clinician whether a change is safe and when it should happen, and let the lab know what you take so the result is read in context.
Watch out: A suppressed TSH on levothyroxine is often the intended effect of the dose, not a sign of hyperthyroidism, reading it without the medication history is a common source of confusion.
Reproductive and adrenal panels deserve the same mapping. Testosterone and estradiol assays can be shifted by exogenous hormones, by SHBG-changing medicines, and by biotin; cortisol assays can be shifted by glucocorticoids, by estrogen-containing medicines that raise binding proteins, and by timing of the draw.
How Long to Stop Vitamins Before a Blood Test
Many people ask whether they need to stop vitamins before labs. The answer depends on the test and the supplement, so there is no single universal timeframe. Common practical guidance includes:
Biotin: Labs often ask people to pause biotin for a period before a draw, and the exact window varies by test.
Other multivitamins and single supplements: Your clinician or lab may recommend a short pause for specific markers.
Prescriptions: Do not stop them without medical advice.
Labs and clinicians vary in their instructions, so confirm the exact window for your panel before you stop anything.
Do Steroids Affect Blood Test Results?
Yes, and the way they do it is the part most people miss. Steroids can change a result in two completely different ways, and the distinction decides what to do next.
The first is a real physiological effect. Corticosteroids such as prednisone, and longer-term inhaled or topical forms, suppress the body's own cortisol production through the HPA axis.
The second is analytical interference, where the medicine gets in the way of the assay itself. This is less common with steroids than with biotin, but it happens, and it is why the assay method matters.
Why the distinction matters: a real physiological effect usually means the medicine is working as intended and the result should be interpreted with the dose and timing in mind. Analytical interference usually means the number itself is unreliable and a different method or a repeat draw is the better move.
A practical follow-up pathway looks like this:
Disclose: Tell the clinician and the lab about every steroid, including short courses, inhaled forms, topical creams, and any anabolic use.
Time it: Note the dose and how recently it was taken, because the interval since the last dose changes the reading.
Review: Have the ordering clinician read the result against the medication history rather than in isolation.
Repeat or re-method: If interference is suspected, a repeat draw or an alternative assay can settle the question.
Do not self-adjust: Never stop or taper a steroid on your own before testing; that decision belongs with the prescribing clinician.
Watch out: A short course of prednisone taken days before a draw can suppress cortisol enough to look like adrenal insufficiency, the timing, not a new condition, is often the explanation.
Your Next Step: Preparing for an Accurate Hormone Panel
An accurate panel starts before you walk into the lab. Use this checklist to prepare:
Write down every prescription, over-the-counter drug, and supplement you take, with doses.
Note any biotin or high-dose vitamin use and the dates you started or stopped it.
Ask your clinician which medications, if any, should be paused and for how long.
Confirm fasting and timing instructions with the lab.
Share the full list with the practitioner who will interpret your results.
If you want help making sense of a panel that doesn't match how you feel, you can book a consultation with The Hormone Boss to review your history and next steps with a clinician who focuses on personalized functional hormone health. You can also compare functional hormone testing options to see which approach fits your situation.
Frequently Asked Questions
What medication should you not take before bloodwork?
No single medication is off-limits by default, and stopping a prescription on your own can be unsafe. Biotin and some other supplements are the most common culprits for hormone and thyroid assays, so they are usually the first items a clinician asks you to pause. Bring a complete list of everything you take, including over-the-counter products and supplements, to your appointment. Your clinician can then tell you which items to hold, for how long, and which should continue. Ask the laboratory whether it has a biotin or medication guideline for the specific test you are ordering.
Can biotin interfere with hormone test results?
Yes. Biotin, a B vitamin often sold for hair and nail health, can interfere with many immunoassays that use biotin-streptavidin binding technology. This can cause falsely high or falsely low results for thyroid tests such as TSH, free T4, and free T3, and it can affect some hormone assays as well. Because the effect depends on the assay method and the dose, the common guidance is to check with your clinician and laboratory about how long before the draw to stop biotin. Do not assume a normal result rules out interference if you have been taking high-dose biotin.
How long should you stop vitamins before a blood test?
The timing depends on the vitamin and the test. Multivitamins containing biotin are a priority to review, while many other vitamins do not affect most hormone assays. Laboratories and clinicians often recommend a pause of several days for high-dose biotin, but the exact window should come from your care team and the laboratory performing your test. Never stop a prescribed medication or a supplement you take for a medical reason without asking first. Writing down what you stopped and when helps your clinician interpret the results accurately.
Can steroids affect hormone test results?
Yes. Corticosteroids such as prednisone can change cortisol, glucose, and some immune and inflammatory markers, and they can influence other hormone levels through their effects on the body. Some oral contraceptives, androgens, and hormone therapies also shift the results of hormone panels. Tell your clinician about every steroid, hormone product, or contraceptive you use, including topical and injected forms, so the results can be read in context rather than mistaken for a new imbalance.
