Data provided by Applied Health
side effects, nutrient depletions, herbal interactions and health notes:
• Iron supplementation may reduce the absorption of Synthroid. Avoid calcium and iron supplements within 4 hours of the medication.1
• Some dietary supplements contain iodine in the form of sea kelp. This nutrient may affect thyroid balance. Consult your pharmacist for more information.2
• Caution in diabetes, the drug may raise glucose levels. Monitor levels while on levothyroxine.3
• Avoid taking soy products with levothyroxine it may decrease absorption of the drug.4
• Ingestion of soy products simultaneously with thyroid hormones appears to reduce the absorption of the hormones.5
• To be safe, people taking thyroid medication should not consume soy products within three hours of taking their medication. In addition, infants with congenital hypothyroidism given thyroid medication must not be given increased or reduced amounts of soy-based formula without consulting a pediatrician or pediatric endocrinologist.6
• Calcium supplementation should be separated by at least four hours from the taking of this medication.7
• Iron deficiency may result in the body's inability to produce thyroid hormones. Ask your physician if you have an iron deficiency. Supplementation of this mineral may help your body in its normal thyroid function, particularly if you are on a restricted or low calorie diet.8
• Thyroid hormone medications taken with food may result in a decrease absorption of the medication. Separate taking this medication by at least two hours from foods.9
References1 The Medical Letter Handbook of Adverse Drug Interactions, 1995.
1 Beard JL, Borel MJ, Derr J. Impaired thermoregulation and thyroid function in iron deficiency anemia. Am J Clin Nutr 1990;52:813-19.
1 Pronsky, Z Food Medication Interactions, 11th edition, 1999
2 The Medical Letter Handbook of Adverse Drug Interactions, 1995.
2 Beard JL, Borel MJ, Derr J. Impaired thermoregulation and thyroid function in iron deficiency anemia. Am J Clin Nutr 1990;52:813-19.
3 Facts and Comparisons, Clinisphere 2.0, Wolters Kluwer Company, 2000
3 Pronsky, Z Food Medication Interactions, 11th edition, 1999
4 Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280-82.
5 Reference not available.
6 Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280–2
7 Schneyer CR. Calcium carbonate and reduction of levothyroxine efficacy. JAMA 1998;279:750.
7 Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA 2000;283:2822-5.
8 Beard JL, Borel MJ, Derr J. Impaired thermoregulation and thyroid function in iron deficiency anemia. Am J Clin Nutr 1990;52:813-9.
8 Beard J, Borel M, Peterson FJ. Changes in iron status during weight loss with very-low-energy diets. Am J Clin Nutr 1997;66:104-10.
8 Campbell NR, Hasinoff BB. Iron supplements: A common cause of drug interactions. Brit J Clin Pharmacol 1991;31:251-5.
8 Campbell NR, Hasinoff BB, Stalts H, et al. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Intern Med 1992;117:1010-3.
9 Liel Y, Harman-Boehm I, Shany S. Evidence for a clinically important adverse effect of fiber-enriched diet on the bioavailability of levothyroxine in adult hypothyroid patients. J Clin Endocrinol Metab 1996;81:857-9.
9 Threlkeld DS, ed. Hormones, Thyroid Hormones. In Facts and Comparisons Drug Information. St. Louis, MO: Facts and Comparisons, Jun 1991, 132-3c.
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The information in Drug Watch is provided as a courtesy to NewsTarget readers by Applied Health Solutions in cooperation with Healthway Solutions. Although the information is presented with scientific references, we do not wish to imply that this represents a comprehensive list of considerations about any specific drug, herb or nutrient. Nor should this information be considered a substitute for the advice of your doctor, pharmacist, or other healthcare practitioner. Please read the disclaimer about the intentions and limitations of the information provided on these pages. It is important to tell your doctor and pharmacist about all other drugs and nutritional supplements that you are taking if they are recommending a new medication. Copyright © 2007 by Applied Health Solutions, Inc. All rights reserved.