Drugs for hypothyroidism, or low thyroid activity, consist of thyroid hormones that supplement the natural hormones in your body. Anti-thyroid medicines treat hyperthyroidism. These prevent your thyroid gland from producing excess hormones. Since numerous drugs interact with grapefruit, check with your doctor before eating it.
Levothyroxine
Certain chemicals in grapefruit interfere with enzymes that metabolize, or break down, some medications. This can cause more medication to stay in your body, raising the medicine's potency to potentially dangerous levels. Grapefruit affects your body's metabolism of the hypothyroidism medication levothyroxine by slightly delaying its absorption. However, grapefruit appears to have only a minor effect on the drug level in your body, according to a 2005 "British Journal of Clinical Pharmacology" study. Thus, the clinical relevance of a grapefruit-levothyroxine interaction is most likely small, according to lead study author J.J. Lilja. To be on the safe side, consult your doctor before combining levothyroxine and grapefruit.
Other Hypothyroid Drugs
Another hyporthyroid drug, thyroid desiccated, does not appear to react with grapefruit, according to Drugs.com. However, this drug may interact with other medications such as digitalis glycosides by raising the levels of digitalis to potentially toxic levels. The hypothyroid drug liotrix also appears not to interact with grapefruit, according to the University of Florida drug interaction database. Though drug interaction databases do not flag these drugs as contraindicated with grapefruit, you should consult your doctor before combining them with this fruit or its juice.
Hyperthyroid Medications
Drugs commonly used for hyperthyroidism include liothyronine and methimazole. The University of Florida drug interaction database does not flag an interaction with grapefruit for either of these medications. However, the database notes that no studies on this specific interaction exist, so consult your doctor before combining grapefruit with either of these drugs.
Beta Blockers
Your doctor may also prescribe beta-blockers if you have hyperthyroidism until you bring the condition under control. These can prevent palpitations by reducing a rapid heartbeat, though they will not reduce your thyroid levels. It is safe to take beta-blockers with grapefruit, according to "American Family Physician," but check with your doctor first.
References
- Drugs.com: Thyroid Drugs; July 2011
- MayoClinic.com: Hyperthyroidism -- Treatments and Drugs; December 2010
- MayoClinic.com: Grapefruit Juice; Katherine Zeratsky; November 2010
- "American Family Physician"; Management of Grapefruit-Drug Interactions; Amy L. Stump, et al.; August 2006
- "British Journal of Clinical Pharmacology"; Effects of Grapefruit Juice on the Absorption of Levothyroxine; J.J. Lilja, et al.; 2005
- Drugs.com: Drug Interactions Between Grapefruit and Thyroid Desiccated; 2011
