Levoxyl is a brand name of the generic drug levothyroxine. Levothyroxine is a synthetic thryoid hormone prescribed to treat hypothyroidism. There are a number of drugs, supplements and foods that interfere with the absorption of levothyroxine, so be sure to discuss your diet and supplement regimen with your doctor.
Because altered levels of thyroid hormone can cause bone loss and increase the risk of developing osteoporosis, many patients who take levothyroxine also take calcium supplements. Calcium inhibits the absorption of levothyroxine, and must be taken separately from levothyroxine by at least four hours. In a 2004 survey published in the “Internet Journal of Advanced Nursing Practice,” more than 80 percent of patients who were taking both levothyroxine and calcium supplements reported taking them within four hours of one another, which can lead to insufficient or uneven absorption of levothyroxine. Antacids that contain calcium should also be taken at least four hours apart from levothyroxine doses.
Like calcium, iron binds with thyroid hormones or levothyroxine, creating an insoluble compound that prevents the hormones from being properly absorbed and may result in hypothyroidism. Most multi-vitamin supplements contain iron, which may be listed as ferrous sulfate. Take iron or any supplement containing iron at least four hours before or after you take levothyroxine, according to DailyMed.
Magnesium also interferes with the absorption of levothyroxine and should be taken at least four hours before or after you take the drug. Most multivitamins contain magnesium, but you may be surprised to find magnesium in your antacids or laxatives. Check the labels of any supplements you take and be sure to inform your doctor of all of them – even antacids and laxatives.
In addition to watching out for supplements that interfere with levothyroxine, you should also be aware that certain foods interfere with its absorption. You should not have soy milk, tofu and other foods that contain soy within two to three hours of taking levothyroxine. Also to be avoided are walnuts, cottonseed meal and high fiber foods.
- University of Maryland Medical Center; Possible Interactions With: Magnesium; Ernest B. Hawkins and Stephen D. Ehrlich; May 2007
- "Food Medication Interactions, Fifteenth Edition"; Zaneta M. Pronsky; 2008