While several citrus fruits can interact with medications, grapefruit is probably the best known. Grapefruit and grapefruit juice can interfere with a number of medications, including several used to treat hypertension, the medical term for high blood pressure. Anti-hypertensives fall into a number of different categories; grapefruit does not interfere with all of them. Talk to your medical practitioner about the effects of grapefruit on the medications you take.
Medications
The antihypertensive medications most affected by grapefruit belong to the calcium channels blockers class. Calcium channel blockers interfere with calcium passage into muscles that control how much a blood vessel constricts. Constriction, or narrowing of the blood pressure, causes blood pressure to rise. Because muscles need calcium to contract, restricting the amount of calcium that enters the muscles of the blood vessel allows it to relax and widen, which lowers blood pressure. Common calcium channel blockers include diltiazem, felodipine, nicardipine, nifedipine, nimodipine and verapamil. Grapefruit may also interfere with a beta blocker, carvedilol.
Actions
Grapefruit contains enzymes that interfere with the enzymes that break down medication. Since the medications don't get properly broken down, or metabolized, higher levels of the drug remain in your system. This increases the chance of developing side effects from the medication.
Timing
Grapefruit can interfere with a drug's absorption within 30 minutes after a single glass of grapefruit juice and can last up to three days after the last intake. A single 8-oz. glass of grapefruit juice is enough to have an effect on medication absorption, pharmacist Sam Shimomura reports in "Pharmacy Times". Grapefruit juice can increase the blood concentration of certain medications several-fold, Shimmura states.
Side Effects
Typical side effects of calcium channel blockers and certain beta blockers that might be more likely to occur if you ingest grapefruit while taking calcium channel blockers include abdominal pain, constipation, drowsiness or fatigue, water retention, headaches, nausea, heart palpitations, hot flashes or sore throat. Calcium channel blockers may lower blood pressure too much, causing dizziness or lightheadedness. Swelling in the legs and shortness of breath can occur from heart failure that occurs as a result of fluid retention. Depression and paranoia can occur, along with an increase in breast size, called gynecomastia, in men. Rarely, chest pain or heart attack can occur.
