Doctors have a variety of medications at their disposal to treat disease, illness and disorders. These medications produce a chemical reaction in the body that is supposed to result in a positive change toward health. However, these medications do not operate in a vacuum and have the potential of interacting with other medications and foods. These interactions can cause medications to produce higher or lower blood levels or can cause other unintended physical changes. Grapefruit is one of the citrus fruits that can impact a variety of medications, including those taken to treat thyroid conditions.
Thyroid Disease
Thyroid medications are used to treat hypothyroid disease, when your body does not produce and secrete enough thyroid hormone to support optimal health. Without hormonal replacement, doctors at the University of Maryland Medical Center warn that you may suffer from myxedema. This can result in a medical emergency when your level of hormones becomes extremely low and may lead to coma and death. Although rare, it can be precipitated in someone suffering from hypothyroid disease by an infection, illness or exposure to cold weather or specific medications.
Absorption
Absorption of thyroid medications occurs in the gastrointestinal tract, according to Abbott Laboratories, manufacturer of the thyroid medication Synthroid. Between 40 percent and 80 percent of the medication is absorbed from the small intestines. The percentage of drug absorbed is increased when taken on an empty stomach and decreased when taken with foods. Taking thyroid medication with fiber will also decrease the metabolism and absorption of these drugs. Enzymes inside the intestinal tract are responsible for the breakdown of medication and transportation into the bloodstream.
Interference
Doctors at Harvard Medical School Family Health Guide warn patients that absorption of thyroid medications may also be inhibited by the presence of grapefruit juice or fruit in your diet. Grapefruit will bind to one of the enzymes in the intestinal tract that is responsible for the absorption of thyroid medication. When the chemical in grapefruit binds to the CYP3A4 enzyme, it becomes easier for the medication to pass from your intestines into your bloodstream, raising the level of medication abnormally high.
Levels of Thyroid Medication
Doctors in Canada discovered that grapefruit affected the absorption level of medication in the early 1990s when they were investigating the relationship between the metabolism of alcohol and a blood pressure medication. They accidentally discovered that taking the medication with grapefruit juice caused dangerously high levels of the medication, almost four times greater than expected. However, doctors from Finland published their findings in the "British Journal of Pharmacology" in 2005, investigating the same effects using the thyroid medication levothyroxine. They found that while this effect was present, there was only a minor change in the bio-availability of the medication and the clinical relevance was thought to be small.
References
- University of Maryland Medical Center: Hypothyroidism
- RxAbbott: Synthroid
- Harvard Medical School Family Health Guide: Grapefruit and Medication
- The People's Pharmacy: Graedons' Guide to Grapefruit Interactions
- "British Journal of Pharmacology"; Effects of Grapefruit Juice on the Absorption of Levothyroxine; J.J. Lilja, K. Laitinen, P.J. Neuvonen; September 2005
