I thought I’d start a nice new thread for this, instead of cluttering up dirty99’s thread (sorry!)
Anyway, continuing from what was originally discussed here(bottom of page 1):
GRAPEFRUIT JUICE DRUG INTERACTIONS
This food-drug interaction was actually discovered by accident. A study that was intending to test the interaction of alcohol and a blood pressure medication, used a mixture of alcohol with grapefruit juice to disguise the taste of alcohol for the study. Ironically, alcohol had no effect on the tested medication, but the grapefruit juice seemed to enhance the absorption of the drug.
The researchers then confirmed the finding by comparing drug levels when taken with either grapefruit juice or water and found five-fold higher blood levels of the drug when it was taken with juice. Orange juice did not show this effect.
Grapefruit juice inhibits a special enzyme (CYP3A4) in the intestines that is responsible for the natural breakdown and absorption of many medications. When the action of this enzyme is blocked, the blood levels of these medications increase, which can lead potentially toxic side effects from the medications.
Research has suggested that flavonoids and/or furanocoumarin present in Grapefruit are the substances that act to block the enzyme in the intestines that normally metabolizes many drugs.
Some medications that interact with grapefruit juice:
Statins (Cholesterol Lowering Drugs)
Calcium Channel Blockers (Blood Pressure Drugs):
Anti-convulsant: Tegretol (Carbamazepine)
Anxiolytics: Valium (Diazepam)
Anti-depressant: Sertraline Clomipramine
Oestrogens: Ethinyl estradiol
Anabolic Steroids: Dianabol
Impotence Drug: Viagra
Although some drugs are given with others to enhance their effects, grapefruit juice should not be used for this purpose because its impact can be unpredictable and potentially dangerous.
The above list is by no means exhaustive. Please consult with your doctor or pharmacist regarding possible interactions between grapefruit juice and medications you may currently be taking if you consume grapefruit/ juice regularly.
[i]Grapefruit juice-drug interactions.
Bailey DG, Malcolm J, Arnold O, Spence JD.
Department of Medicine, London Health Sciences Centre, Ontario, Canada.Br J Clin Pharmacol. 1998 Aug;46(2):101-10.