Our Members Asked:
Which vitamins and supplements should be stopped before getting blood work, laboratory tests, or medical imaging?

Answer:
There are a number of supplements that may interfere with blood, urine or stool tests, and even certain imaging tests. This can cause misleading results or lead to unnecessary additional testing or treatment.
More specifically, supplements can affect:
- Thyroid and other hormone tests
- Vitamin D and calcium tests
- Prostate specific-antigen (PSA) tests
- Tests for hepatitis B and hepatitis C
- Tests of kidney function (blood levels of creatinine)
- Tests for glucose, bilirubin, hemoglobin, calcium, chloride, and magnesium
- Certain COVID-19 tests
- Troponin tests used to help diagnose heart attacks
- Hydroxyproline tests (for osteoporosis and other bone diseases)
- Bone density scans
- MRIs (magnetic resonance imaging)
- Certain stool tests that may be used to screen for colon cancer and gastrointestinal bleeding
- Pregnancy (hCG) tests
- Anti-doping tests for athletes
The supplements that can cause these interactions include B vitamins such as biotin, niacin and riboflavin, as well as calcium supplements, creatine, iron supplements, St. John’s wort, vitamin C, L-tryptophan, and 5-HTP, as well as certain foods and drinks. High-dose N-acetyl cysteine (NAC) may also interfere with certain tests, although this may depend on how it is administered.
Sign in as a member to learn which vitamins and supplements interfere with which tests, when to stop taking these supplements before tests to avoid interference.
Be sure to tell your physician and laboratory about all the supplements you take, as interference may vary depending on the exact model of test used and can change when tests are updated or reformulated.
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Monica C
November 27, 2024I discovered that a glucosamine supplement I was taking was causing alarming liver enzyme test results. Multiple tests, even an endoscopy and biopsy showed no problems. I stopped the glucosamine and test results dropped down to normal. I also found some data about the effect.
You can find information about this in the Concerns and Cautions section of our Joint Health Supplements Review https://www.consumerlab.com/reviews/review-glucosamine-chondroitin-msm-boswellia-supplements/jointsupplements/#glucosamine-liver-toxicity.
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Jude :-)
September 11, 2024Wow, never had been advised about any of this prior 2 any of my lab tests, ever! Thank "U "
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Sandra20630
September 10, 2024Interesting, I'd just found this out on my own after having gone downhill for about 7 years, and with 2 years of worsening heart problems. I've been hypothyroid for many decades and was on a fair dose of a good thyroid medication but suspected my thyroid - so went investigating. What I discovered led me to pay out of pocket for ft3 ,ft4, and tsh labs after being off b vitamins for a week. Past tests had always shown high normal results, when in fact my test graph plummeted well below the whole chart for ft3 and 4 after removing the b vitamins that included biotin. Now, on the correct dose, my heart problems are resolving along with so many other things related to low thyroid. I told many friends who found that their doctors, and even endocrinologists, weren't aware of this! Many were on the wrong dose, it turned out. Anyone with thyroid issues knows how this will impact every facet of their lives. Hopefully the professionals will read this.
Mary22139
March 04, 2025I experienced low free T3 and T4 with normal TSH taking 5 mg of biotin daily. I also experienced low T3 and T4 with normal TSH taking 168 mg elemental sustained release magnesium at night. In both cases, values returned to normal after stopping these two supplements. I am hoping I can resume taking the magnesium earlier in the day.
See our article about supplements that may interfere with thyroid medication https://www.consumerlab.com/answers/do-any-supplements-interfere-with-thyroid-hormones/hypothyroidism-and-supplements/.
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Mary19288
April 14, 2024Thanks, ConsumerLab!! And this... is why I subscribe.
Marleina20636
September 10, 2024I recently had blood work & my pcp had me stop taking magnesium (which did not make me happy). He said it interfered with my potassium. I have tried researching this w/o much luck.
We are not aware of evidence indicating that magnesium influences laboratory measurements of potassium levels, but magnesium may affect levels of potassium levels in the body, as highlighted in our Potassium Supplements Review: https://www.consumerlab.com/reviews/potassium-supplements-review/potassium/#using-taking
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Researcher
July 15, 2023WoW! Thank you so much for this information! I had no idea. I just had a annual blood test and my thyroid was off. I do take supplements and am retesting in 6 weeks as my php said it was confusing relating to other results. I will also check back on here a month before blood work for additional info. THANK YOU! CONSUMER LAB!
Thank you for your kind words, we're glad you found the information helpful.
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marlene17416
July 11, 2023I was advised to stop fish oil, turmeric and vitamin e before a medical procedure because of bleeding risk. Surprised at the number of supplements’ cautions regarding tests and procedures. I now look up all my individual supps. before
Med tests.
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terri17414
June 12, 2023does taking collagen powder interfere with bone marker tests, particularly urine tests?
We've added information about this in the answer above, and more details can be found in the "Concerns and Cautions" section of our Collagen Supplements Review https://www.consumerlab.com/reviews/collagen-supplements-review-peptides-hydrolysate/collagen/#bone-tests.
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Jada
June 02, 2023Great information! Thanks
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Laura47
March 23, 2023Thank you… Very helpful post.
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Researcher
February 21, 2023THANK YOU SOOOO VERY MUCH. I had no idea.
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Glad you found it helpful Sandra!
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Sandra Collins
February 12, 2023Thank you so much for that helpful info. My Dx’s never told me about any of this!
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raymond17407
February 07, 2023Don't forget about Red Yeast Rice or other "natural statin" supplements raising liver enzymes.
See the "Concerns and Cautions" section of our Red Yeast Rice Supplements Review for more about the potential effects of red yeast rice supplements on the liver https://www.consumerlab.com/reviews/red-yeast-rice-supplements-review/red-yeast-rice/#liver.
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Maureen17406
February 07, 2023I had no idea, thanks!
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Marcella17405
February 07, 2023Thanks for this info. I get a full body bone scan every 6 mos. and no one
at facility ever told me not to take calcium before test.
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Tracy3333
February 07, 2023thanks love hearing these kinds of info
You're welcome Tracy, glad to hear it's helpful!
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Shelia17400
August 26, 2022This information is very beneficial. Thank you!
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Researcher
July 17, 2022This is very helpful. I had no idea. It is an excellent and important reminder, that supplements in any form need to be discussed with your doctor. It is also important as WE must take steps to be informed on anything we ingest before having blood work.
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Petr17394
July 10, 2022Great
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Joann17393
July 10, 2022Thanks!
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Judith17390
July 08, 2022Many thanks
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Cheryl17387
July 08, 2022What an excellent review! Thank you Consumer Lab.
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Sarafina17386
July 08, 2022Thanks. Very helpful.
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Linda17380
July 08, 2022As a person who has frequent lab work, I find this very helpful. Thank you.
Thank you for your kind words Linda, we're glad to hear it's helpful for you!
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Rattattat
July 08, 2022I recently started taking Biotin to help with my hair. I am hypothyroid and when I took my thyroid blood test the result that came back was off the chart crazy . I had to go to an endocrinologist to find out about Biotin.
She said to discontinue for a week before any future tests, and if I had any visits to the ER always tell them that I take Biotin or the blood test results will make them think I'm having a heart attack.
raymond17378
February 07, 2023Wow, good endo! I've got an endocrinologist neighbor who had NO IDEA what Reverse T3 is.
Sandra Collins
February 12, 2023That is sad, but not surprising.
Danielle17376
June 02, 2023Yes for me it is a week with no vitamins.
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