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Patient’s Attempt to Increase Potency of Medication

Feb 11, 2013

Last week we had a patient come in to the pharmacy with a prescription for sildenafil 100 mg to be used as directed.

We asked the patient the normal questions about taking nitrates or any other heart-related medications and it appeared that it would be all right to fill the prescription.

The patient came back to get the prescription and we checked to make sure that he knew when to take the medication, which he was very clear on. As he was paying for the prescription he asked what aisle the grapefruit juice was on. While the technician was checking the directory, the patient stated that he could increase the effect of the sildenafil by drinking grapefruit juice with the medication. When I quizzed him on this he let me know that he had been listening to a radio show about the interactions of medications and grapefruit juice and the researcher had said that the juice could block the breakdown of the sildenafil and could increase the effective dose.

We instructed the patient not to do this as it would be impossible to know how much increase in dose would occur and could lead to problems.

Lesson Learned:

We often speak of possible interactions when we speak to patients about medications and food choices that may decrease effectiveness of the medications, but we need to also let those patients know when an increase of effectiveness can occur.

Ken Oaster, PharmD


Bailey DG, Dresser G, Arnold JMA. Grapefruit and medication interactions: forbidden fruit or avoidable consequences? CMAJ 2012; DOI:10.1503/cmaj.120951. Copyright © 2012 Canadian Medical Association


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