Drinking grapefruit juice while taking certain medications inhibits enzymes produced in the intestine. These enzymes help the body metabolize those medications through the process of elimination, according to Drugs.com.
Chemical compounds in grapefruit known as furanocoumarins bind to the enzymes, explains HealthBeat. This binding decreases the enzymes' ability to break down the medication, keeping them from efficiently eliminating the toxins and leading to a faster and higher absorption rate into the bloodstream, states Drugs.com. When drug levels in the blood rise, so do the risks of new, worsened or even toxic side effects.
Grapefruit juice's effect on medications is not just a momentary phenomenon. This binding effect can potentially last for 24 hours or longer, which is why those on certain drug therapies should avoid grapefruit juice completely. Grapefruit is not the only citrus fruit known to have these adverse effects, reports HealthBeat. Seville oranges and tangelos could also present an interaction risk, although studies are not as thorough, as of 2015.
This interaction between citrus fruits and medication occurs with several categories of drugs, with statins, typically taken to lower cholesterol levels, at the top of the list, notes WebMD. Other medications that potentially interact with grapefruit juice include some antihistamines, anti-anxiety and pain medications, and medications treating erectile dysfunction.