Synthroid Interactions With Vitamins

Certain vitamins can interact with synthroid.

Synthroid is a prescription drug that can be used to treat hypothyroidism. Although there are many types of thyroid disorders, hypothyroidism remains the most common, affecting millions in the United States. While hypothyroidism occurs in both men and women, it is more prevalent in women, according to the National Institutes of Health.


The thyroid is a small gland responsible for producing hormones and influencing metabolism. There are two types of hormones the thyroid creates: tri-iodothyronine, or T3, and thyroxine, or T4. These hormones influence the way your body metabolizes food, favoring it either for immediate energy or for storage. When the thyroid gland becomes underactive, it produces less thyroid hormone and is referred to clinically as hypothyroidism. This can result in symptoms such as weight gain, poor growth and lack of energy and is typically treated by replacing the hormone the body lack, notes the Hormone Foundation website.



Synthroid – also known as levothyroxine – is a synthetic version of T4. Although it is typically used to treat hypothyroidism, it is also used for other conditions. Taking synthroid usually reverses symptoms of hypothyroidism, but it does not cure the condition. Symptoms may take up to several weeks to reverse, according to the National Institutes of Health.

Nutritional Intake and Synthroid

Follow your normal diet when taking synthroid, unless your doctor recommends otherwise. Side effects such as a change in appetite, nausea, vomiting or weight loss can occur. You may also experience other side effects such as stomach cramps, headache, tremor, nervousness or increased appetite. These symptoms can affect your dietary intake, so be sure to consult your doctor if you experience any of these.


Vitamin Interactions

Iron, calcium or magnesium supplements can decrease absorption of synthroid and should be taken separately by at least four hours. Let your doctor know whether you are taking any supplements that contain these vitamins. Additionally, foods such as walnuts, soy products and high-fiber foods may also decrease absorption of the drug. Take synthroid at least two hours before eating these foods. Typically, your doctor will monitor your thyroid function to make sure these vitamins and foods are not interacting with your medication.


Take synthroid exactly as indicated on your prescription. If you have questions about your diet, supplements or interactions with other medications, consult your doctor and pharmacist.