what chemical is in  grapefruit juice
Drugs or toxins are broken down (metabolized) so that they can be eliminated from the body. Grapefruit juice decreases the activity of the cytochrome P450 3A4 (CYP3A4) enzymes that are responsible for breaking down many drugs and toxins. Grapefruit contains compounds known as furanocoumarins that block the CYP3A4 enzymes. When grapefruit juice is consumed, the enzymeâs ability to break down the drug for elimination is decreased. Blood levels of the drug may rise, resulting in the risk for new or worsened side effects.