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Can Vitamin C Affect Synthroid?

author image Beth Richards
Beth Richards, a freelance writer since 2002, writes about health and draws from her 25 years as a licensed dispensing optician. She has authored several books, writes for national magazines including "Country Living" and "Organic Family" and is a health and wellness features writer for several publications. She is earning a Bachelor of Arts in English from the University of Maryland.
Can Vitamin C Affect Synthroid?
A man is drinking a glass of orange juice. Photo Credit: Visual Ideas/Camilo Morales/Blend Images/Getty Images

Ask your doctor if you should take your Synthroid or other thyroid medicine with your morning orange juice. A 2008 study in the "International Journal of Endocrinology and Metabolism" suggests that vitamin C helps thyroid medicines work better. Check with your health-care practitioner before taking any supplements with thyroid medication; food, vitamins and medication are known to alter the potency of thyroid hormones.

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Synthroid is the name of a prescription medication made by Abbott Laboratories. The active ingredient in Synthroid is levothyroxine, a synthetic thyroid hormone that is just like the hormone made by your thyroid gland. Synthroid is prescribed for hypothyroidism, also called "slow" thyroid. Certain foods and supplements affect the way your body absorbs the medicine.

Synthroid and Absorption

According to the manufacturer, you should not take Synthroid within four hours of ingesting anything that may interfere or interact with the hormone. Certain medications and foods alter the way Synthroid is processed in the body. Abbott Laboratories' website,, notes that dietary supplements also disrupt your body’s absorption of Synthroid and instructs patients to discuss Synthroid and supplement intake with their doctor.

Vitamin C and Synthroid

In the 2009 issue of "Thyroid International," Dr. Kenneth Burman of Washington Hospital Center lists vitamin C as one of the factors that change levothyroxine's gastrointestinal absorption. Burman says that, as of 2009, there was only the 2008 study on vitamin C and its effect on thyroid hormones. The results of the 2008 research showed significant improvement of levothyroxine absorption when taken with 1 g of vitamin C, but Burman suggests that more studies should be done to determine if the same effect could be achieved at different doses.

Considerations and Warning

Follow your doctor's directions for taking Synthroid. Ask your pharmacist or health-care provider before stopping or starting any type of supplements, including vitamin C, while taking levothyroxine.

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