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Frequently Asked Questions

Does grapefruit juice affect Viagra and Cialis? What about orange or apple juice?

Short Answer

We recommend that grapefruit juice not be taken at the same time as Viagra or Cialis. Orange and apple juice do not contain the same compounds as grapefruit juice, so they do not cause problems with these drugs.

Long Answer

Drinking a glass of grapefruit juice has long been known to help with the body's absorption of some drugs. However, scientists now believe that grapefruit juice can have a negative impact on the body's absorption of many widely-prescribed medications. It is believed that flavanoids in the juice decrease the levels of certain intestinal enzymes that would otherwise break down many drug molecules before they reach the bloodstream. More medication then reaches the bloodstream and may cause an overdose, with serious consequences for the patient.

With other Men's Health medications like Sildenafil Citrate (Viagra, Silagra) and Tadalafil (Cialis, Tadacip), grapefruit juice inhibits the body's absorption of the medication. The substances in the juice that do this are called furanocoumarins. They activate one of the body's naturally-produced drug efflux mechanisms, known as P-glycoprotein, located in the intestinal tract. When grapefruit juice interacts with P-glycoprotein, the result is an increased likelihood that certain drugs will be stopped from entering the bloodstream. Viagra and Cialis are therefore less effective when grapefruit juice is present in the body.

There are more than 50 commonly-prescribed drugs that use the same pathways and have the same negative interactions with grapefruit juice, including those prescribed for the treatment of high cholesterol, depression, high blood pressure, cancer, pain, Erection (Erectile) Dysfunction and allergies.

Additional Information

Grapefruit may reduce the effectiveness of other prescription drugs. Examples include vinblastine (Oncovin), etoposide, ifosfamide (Ifex), sildenafil (Viagra), quinidine, losartan (Cozaar), digoxin (Lanoxin), theophylline (Slo-Bid), itraconazole (Sporanox), amprenavir (Agenerase) and fexofenadine (Allegra).

www.drwearwellness.com

Grapefruit affects the activities of many drugs, with potentially serious effects. Interactions with various drugs (prescription or over-the-counter) can occur when using any part or form of grapefruit, including grapefruit juice or peel. Patients taking prescription drugs who are considering using a product that contains grapefruit are encouraged to talk with their healthcare providers or pharmacists.

www.medicinenet.com

Research about the interaction of grapefruit juice with drugs suggests that compounds in grapefruit juice, called furanocoumarins (e.g. bergamottin), may be responsible for the effects of grapefruit juice. Researchers believe that furanocoumarins block the enzymes in the intestines that normally break down many drugs. One glass of grapefruit juice could elicit the maximum blocking effect, and the effect may persist for longer than 24 hours. Since the effects can last for such a prolonged period of time, grapefruit juice does not have to be taken at the same time as the medication in order for the interaction to occur. Therefore, unlike similar interactions, where the interaction can be avoided by separating the administration of the two interacting agents by a couple of hours, administration of grapefruit juice with susceptible drugs should be separated by 24 or more hours to avoid the interaction. Since this is not practical for individuals who are taking a medication daily, they should not consume grapefruit juice when taking medications that are affected by grapefruit juice.

www.sciencedaily.com

In a study published in the April 1999 issue of Pharmaceutical Research, an American Association of Pharmaceutical Scientists (AAPS) publication, Dr. Andrea Soldner and other scientists at UCSF demonstrate that grapefruit juice can actually inhibit the body's absorption of certain drugs including: Vinblastine (for combating cancer) Cyclosporine (for supressing organ rejection following transplant) Losartan (for controlling high blood pressure) Digoxin (for treating congestive heart failure) Fexofenadine (for alleviating allergy symptoms).

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