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Unithroid oral

Levothyroxine/Soy Formula or Nutritional Therapy

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug, changing your diet or commencing any course of treatment.

Medical warning:

Very important. A change in your diet, medicine, or dosage may be necessary. Promptly consult your doctor or pharmacist.

How the interaction occurs:

Soy formulas or nutritional products 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.

What you should do about this interaction:

Let your doctor know that you are using a soy-based formula or nutritional therapy or if you stop using a soy-based formula. Your doctor may want to monitor your (or your baby's) thyroid function more closely and may need to adjust the dose of levothyroxine while you are using the soy-based product or if you stop using it. Let your doctor know if you notice any of the following signs of hypothyroidism: fatigue, sluggishness, constipation, stiffness, muscle cramps, loss of appetite, excessive weight gain, or dry skin.Your healthcare professionals (e.g. doctor or pharmacist) may already be aware of this interaction and may be monitoring for it. Do not start, stop, or change the dosage of any medicine before checking with them first.

References:

1.Conrad SC, Chiu H, Silverman BL. Soy formula complicates management of congenital hypothyroidism. Arch Dis Child 2004 Jan;89(1):37-40.
2.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.
3.Synthroid (levothyroxine sodium) US prescribing information. Abbott Laboratories June, 2011.
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.

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