KnowHOW team explains: Grapefruit interacts with an enzyme, found mostly in the lining of the digestive tract, that breaks down the fruit as well as many drugs. As a result, less of the enzyme is available to work on the drugs, and higher-than-normal amounts go into the bloodstream, rather than being broken down. For some drugs, the effective dose is so much higher that it can be dangerous, or even fatal.

The enzyme is called P450 34A. In 1989, scientists discovered that grapefruit juice could interfere with the digestion of one of the blood-pressure medications called calcium channel blockers. Since then, the list of drugs with grapefruit warnings has grown.

Some widely prescribed cholesterol-lowering drugs known as statins are of special concern; extra-high levels of the drug can cause damage to the muscles or kidneys. The list also includes some anti-anxiety drugs, antidepressants and sleeping pills; some AIDS drugs, heart drugs and blood-thinners; and some antibiotics.

The effect is long-lasting, persisting 24 hours or more, so eating grapefruit in the morning and taking the drug at night won’t help. For a few drugs, grapefruit activates another digestive chemical, P-glycoprotein, and may prevent the full amounts of the drugs from entering the bloodstream.

The question was sent by Sabina Sheikh from Jamshedpur