I'm taking a medication to lower my cholesterol levels and have recently read an article that says I shouldn't take grapefruit juice while I'm on the drug. The article didn't say why, so can you explain it?
It might seem somewhat strange but grapefruit juice can indeed increase the potency of certain drugs. This is because a particular type of enzyme called CYP 3A4, one of a family of cytochrome P-450 enzymes, has a crucial role in the metabolism of many drugs and toxins.
It works by changing the drug into substances that are either less potent and/ or are more easily excreted by the body. Grapefruit juice interferes with the ability of CYP 3A4 to work effectively, letting more of the drug into the bloodstream, resulting in an increase of its potency.
For some reason grapefruit juice only interacts with this enzyme in the digestive system and not in the liver or other organs where it is also found. This means that certain drugs when taken orally will be affected by consuming grapefruit juice but not when the same drugs are injected into the body.
Does grapefruit juice interfere only with cholesterol drugs or can it interact with other medicines?
Research has shown that the juice can interfere with several different types of medication. Although the interactions can be mild, some have serious consequences. Not everyone produces the same level of cytochrome and not every drug is metabolised in the intestine.
Cholesterol-lowering drugs have increased potency when taken with grapefruit juice, which can cause excessive levels of the drug in the system. In rare cases this may cause a serious and sometimes fatal muscle disorder known as rhabdomyolysis.
Newer anti-depression medications called selective serotonin uptake inhibitors (SSRIs) and certain blood pressure medications can also react with the juice.
Is it just grapefruit or do other citric fruit juices produce the same effect?
Although grapefruit has the strongest effect, lime juice and orange juice made from Seville oranges have been found to inhibit the enzyme in a similar way. Apple juice can also interact with some medications. Just to be on the safe side, avoid fruit juices when taking your tablets - use water instead.