This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.
Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
Soy-based formula and nutritional therapy may decrease how much levothyroxine the body absorbs.
What might happen:
The amount of levothyroxine in the blood may decrease and symptoms of hypothyroidism may occur. Signs and symptoms to look for are: fatigue, sluggishness, constipation, stiffness, muscle cramps, loss of appetite, excessive weight gain, or dry skin.
What you should do about this interaction:
Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Synthroid (levothyroxine sodium) US prescribing information. Abbott Laboratories June, 2011.
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3.Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: the influence of soy-based formula. J Am Coll Nutr 1997 Jun;16(3):280-2.
4.Bell DS, Ovalle F. Use of soy protein supplement and resultant need for increased dose of levothyroxine. Endocr Pract 2001 May-Jun;7(3):193-4.