Can You Take Synthroid (Levothyroxine) With A Multivitamin?

In our latest question and answer, the pharmacist discusses whether or not Synthroid (levothyroxine) can be taken safely with a multivitamin


I take Levothyroxine 137mg. Is it safe to take a b12 vitamin, collagen, and a multivitamin?

Asked by Deb On Feb 03, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Feb 05, 2018

There is a significant interaction between Synthroid (levothyroxine) and multivitamins. Many different substances (foods and minerals such as calcium, aluminum and magnesium) are known to decrease Synthroid (levothyroxine) absorption if taken at the same time. The most common mechanism behind the decreased absorption is due to "chelation".

Calcium, and a variety of other mineral and drugs, can bind (i.e. chelate) to Synthroid (levothyroxine), which can significantly decrease the absorption of the medication. Decreased absorption of Synthroid (levothyroxine) will, in most cases, lead to increased thyroid stimulating hormone (TSH) levels and the need to increase the dose of Synthroid (levothyroxine).

Multivitamins contain multiple ingredients that are known the bind to Synthroid (levothyroxine), decreasing absorption such as:

  • Calcium
  • Iron
  • Magnesium
  • Manganese
  • Potassium
  • Zinc

To ensure consistent absorption of Synthroid (levothyroxine), it is recommended to take the medication on an empty stomach with a full glass of water, at least 30 to 60 minutes before food (most commonly breakfast). It is very important to take Synthroid (levothyroxine) apart from substances known to decrease absorption.

If morning dosing isn't possible, it is important to know that consistency of administration is key to avoid fluctuating thyroid levels in the body (resulting from variable Synthroid (levothyroxine) absorption with interacting substances). Synthroid (levothyroxine) can be taken in the evening, as long as it has been 4 hours after the last meal of the day, when the stomach is mostly empty. 

If it is not possible to separate Synthroid (levothyroxine) from food in your situation, try to take the medication at the same time daily, with the same foods or same interval away from food. This will ensure consistent absorption and thyroid levels in the body.

Below is a list of the most common foods, medications and supplements that are known to decrease Synthroid levels when taken together:

  • Multi-vitamins
  • Antacids (especially calcium and aluminum containing ones)
  • H2 Blockers
  • PPIs (Proton Pump Inhibitors)
  • High calcium foods (e.g. dairy)
  • Bisphosphonates (e.g. Fosamax)
  • Coffee
  • Grapefruit juice
  • Iron
  • Magnesium
  • Bile acid sequestrants
  • Simethicone
  • Soy
  • Fiber

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Office: 716-389-3076

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