Should I stop taking supplements before my blood test?

No, please keep taking your prescribed medications as usual – with a few exceptions on the morning of your blood draw. This allows us to assess your health in the context of your real-life routine.

Please include what you take and the dosage in your questionnaire so our medical team can interpret your results accurately.

On the morning of your test, please pause:

• Iron supplements: stop 24–48 hours before your draw – iron supplements temporarily raise circulating serum iron and can skew your results. Resume your usual dose right after the blood draw. (Fasting also matters for this – see our iron biomarker page for details.)
• Biotin (vitamin B7 – e.g. in hair, skin and nail supplements): at a standard dose (up to 5 mg/day), stop 48–72 hours before your test. It can interfere with several hormone measurements, including thyroid tests, causing falsely low TSH and falsely high free T4/T3. If you take high-dose biotin (over 5 mg/day – e.g. prescribed for hair/nail growth or another prescribed use), extend this to 3–7 days beforehand. A standard multivitamin is fine to continue. If high-dose biotin was prescribed by your doctor, don't stop without speaking to them first, and let us know in the medical questionnaire.
• Thyroid medication (e.g. levothyroxine): take it after your blood draw, not before – taking it beforehand causes a temporary spike in free T4 that affects your baseline result.

Also worth mentioning in your questionnaire:

• Creatine: may influence markers related to kidney function.
• Finasteride or dutasteride (e.g. for hair loss or an enlarged prostate): these lower PSA by about half, so if you're booking the PSA add-on, flag this in your questionnaire so your result is interpreted correctly.