Supplements That May Affect Your Lab Test Results

If you take vitamins or dietary supplements, it's important to let your healthcare provider know before having lab work. Some supplements can interfere with test results, leading to inaccurate readings.

Common Supplements That May Affect Lab Tests

Biotin (Vitamin B7)

Often found in hair, skin, and nail supplements, biotin can interfere with thyroid tests, heart tests, hormone levels, and other blood work. Many providers recommend stopping high-dose biotin 48–72 hours before testing.

Vitamin C Large doses may affect certain blood glucose, urine, and stool tests.

Iron If you're having iron studies, your provider may recommend waiting until after your blood draw to take your iron supplement.

Herbal Supplements Products like ginseng, ginkgo, garlic, and St. John's wort may affect blood clotting or other lab results.

Before Your Lab Appointment

• Tell your healthcare provider and pharmacist about all vitamins and supplements you take.

• Follow any fasting instructions carefully.

• Ask whether you should take your morning supplements before your blood draw.

• Never stop prescription medications unless your provider tells you to.

Need Advice?

If you're unsure whether a supplement could affect your lab work, talk to your pharmacist. We're happy to help you prepare for accurate test results.