While grapefruit juice may be part of a healthy diet, U.S. health officials warned on Wednesday that grapefruit juice and fresh grapefruit can dangerously interfere with the way some prescription and non-prescription drugs work.

The interaction between grapefruit-made products and medication can be seriously hazardous to health, according to Shiew Mei Huang, acting director of the Food and Drug Administration’s Office of Clinical Pharmacology in a statement released today.

Grapefruit juice increases the absorption of the medication into the bloodstream, and when there is a higher concentration of a drug in the bloodstream may be toxic and patients tend to exhibit more side effects, said Huang.

The toxic effect is exhibited in some statin drugs that lower cholesterol. When these cholesterol drugs are taken with grapefruit, too much of the drug’s chemicals can stay in the body, increasing the risk for liver damage and muscle breakdown, which can lead to kidney failure.

Drinking grapefruit juice several hours before or after taking medications can still be risky, so it’s best to just avoid or limit grapefruit juice or fresh grapefruit when taking particular drugs, Huang advised.

The FDA lists examples of some types of drugs that grapefruit juice can interact with:

- statin drugs to lower cholesterol, such as Zocor (simvastatin), Lipitor (atorvastatin) and Pravachol (pravastatin)

- Blood pressure-lowering drugs, like Nifediac and Afeditab (both nifedipine)

- Organ transplant rejection drugs, like Sandimmune and Neoral (both cyclosporine)

- Anti-anxiety drugs, like BuSpar (buspirone)

- Anti-arrhythmia drugs, like Cordarone and Nexterone (both amiodarone)

- Antihistamines, like Allegra (fexofenadine)

The FDA said that while scientists have known that grapefruit juice can cause a potentially toxic level of certain drugs in the body, recent studies have also discovered that the juice has the opposite effect on a few other drugs.

While scientists have known for several decades that grapefruit juice can cause a potentially toxic level of certain drugs in the body, Huang says more recent studies have found that the juice has the opposite effect on a few other drugs.

“Grapefruit juice reduces the absorption of fexofenadine,” said Huang, which in turn decreases the effectiveness of the drug. Fexofenadine (brand name Allegra), which relieves allergy symptoms, may also be less effective if taken with orange or apple juice, and the drug carries a label that states “do not take with fruit juices”.

The opposite effect happens when elements in grapefruit juice block the action of drug transporters, proteins in the body that help move a drug into cells for absorption, resulting in less of the drug being absorbed which may become ineffective in treating some aliments.

Huang said that it has required some prescription drugs to carry labels that warn against consuming grapefruit juice or fresh grapefruit while using the drug, and current FDA investigation into drug and grapefruit juice interaction could result in future label changes for other drugs.

The FDA advises that people should ask their pharmacist about consuming grapefruit or grapefruit juice while using their medication as well as other juices. Patients should carefully read the patient information sheet that comes with prescription medicine as well as the Drug Facts label on your non-prescription medicine.

The agency also suggested checking the bottles of beverages flavored with fruit juice to confirm that they don’t contain grapefruit juice and to avoid Seville oranges and tangelos as well because they produce the same effects as grapefruit.