The safety and effectiveness of a drug may be affected by other medications, foods such as dairy products, vitamin supplements, antacids, and even herbal remedies. These are called drug interactions. Problems caused by interactions between certain prescription medications and grapefruit juice have gotten a great deal of media attention lately, and some of this coverage has caused people to mistakenly assume that grapefruit juice should be avoided with any medication. In reality, the problems with grapefruit juice actually affect very few patients.

What You Should Know
It is important to recognize that most prescription drugs are not affected by grapefruit juice at all. In addition, no interactions have been observed with nonpre-scription medications and grapefruit juice. For those medications that are affected, the interaction can result in higher levels of such drugs in the blood, which may lead to adverse reactions. If your medication interacts and you do not wish to comply with a grapefruit juice restriction, your doctor or pharmacist can generally suggest a noninteracting, alternative medication to treat your condition with no need to avoid grapefruit juice. This option is on a case-by-case basis.

Talk to Your Physician and Pharmacist
It is wise to ask your physician or pharmacist about the potential for any medicine to interact with food, other prescriptions, or common nonprescription remedies. Have him or her explain any potential interactions and side effects as well as the expected benefits of the medicine.  Most pharmacists will make sure you understand such potential interactions and exactly how to take your medication to maximize the benefit and minimize side effects. That?s their job. And be sure to read any information that accompanies your prescriptions, which usually addresses potential interaction problems. Chances are very good that if grapefruit juice is not mentioned either by your pharmacist or in the materials he or she provides you about your medication, then it has no effect on the medication you are taking.

Will I Experience a Reaction?
Whether a patient will experience drug interactions is hard to predict. People react to drugs with great individual variability due to individual genetics. Even medications known to be affected by grapefruit juice may not produce an interaction in a given individual because of his or her genetic makeup. Thus, blood levels of a drug may be perfectly normal despite drinking grapefruit juice every day.  

Which Medications Should I Be Concerned About?
The medications that may interact with grapefruit juice are listed in the Table. If you are concerned about the possibility of a reaction or have already experienced a reaction between your medicine and grapefruit juice, other choices of drugs are available in all classes of medications. Thus, even the potential for an interaction need not spell the end of the enjoyment of a healthful glass of grapefruit juice. 

Of particular concern are interactions with some heart or blood pressure medications that might cause irregularities in heartbeat, called arrhythmia, with unusually high blood levels. Certain cholesterol-lowering medications, called statins, are similarly affected and can increase the likelihood of painful muscle disorders. A few of the medications used to treat serious psychiatric illnesses can also cause such problems.

The important point to understand is that you do not necessarily need to avoid grapefruit juice when taking most medications, and if you have already been taking one of the affected medications and have not experienced any problems, then talk to your doctor or pharmacist about whether or not it is safe to conclude that you need not change anything. For new prescriptions, tell your physician of your grapefruit juice intake, so that he or she can select an appropriate medication. In some cases, a doctor might recommend grapefruit juice in order to increase levels of a medication when the patient has difficulty absorbing enough of the drug to make it effective.



Summary of Known and Anticipated Drug Interactions with Grapefruit Juice*
Magnitude of Interaction: Large Moderate Small or Negligible
Calcium-channel antagonists   Felodipine Amlodipine
    Nicardipine Diltiazem
    Nifedipine Verapamil
HMG-CoA reductase inhibitors (statins) Lovastatin Atorvastatin Fluvastatin
  Simvastatin Cerivastatin Pravastatin
Immunosuppressants   Cyclosporine  
Sedative?hypnotic and anxiolytic agents Buspirone Triazolam Alprazolam
    Midazolam Clonazepam?
    Diazepam Zolpidem?
    Zaleplon? Temazepam?
Other psychotropic agents   Carbamazepine SSRI antidepressants?
    Trazodone? Clozapine
    Nefazodone? Haloperidol
Antihistamines Terfenadine Loratadine? Fexofenadine?
  Astemizole?   Cetirizine?
Human immunodeficiency virus protease inhibitors   Saquinavir Indinavir
Hormones   Ethinyl estradiol Prednisone
    Methylprednisolone Prednisolone
Other drugs Amiodarone Sildenafil? Clarithromycin
    Cisapride Erythromycin
*HMG-CoA = 3-hydroxy-3-methylglutaryl coenzyme A; SSRI = selective serotonin reuptake inhibitor.
?Interactions or noninteractions that have not been studied, but can be reasonably predicted based on available data.
Source: Greenblatt DJ, Patki KC, von Moltke LL, Shader RI. Drug interactions with grapefruit juice: an update [editorial]. J Clin Psychopharmacol. 2001;21(4):357-359.