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CMAJ. 2013 April 2; 185(6): 507–508.
PMCID: PMC3612156

Grapefruit–medication interactions

David G. Bailey, PhD, Scientist

Greenblatt and Derendorf1 have previously acknowledged their conflict of interest as clinical research advisors to the Florida Department of Citrus. That there is “no validated evidence” of “serious adverse effects” of an interaction of grapefruit with any affected medications is their opinion. We have documented published reports in the medical literature that are noted in our recent article.2

That a serious adverse event has not been reported should not be interpreted to mean that it has not happened. To recognize an adverse event, there first must be an awareness of the possibility of such an adverse event. Otherwise, the likelihood that it will be investigated is extremely low. This is mentioned in our article2 and is one of the major reasons why we were compelled to identify and inform the profession and public about this interaction.

Our article2 focuses on the number of new drugs now on the market that have the potential for serious toxicity if administered with grapefruit. The relevance of this aspect is highlighted by a recent publication showing that nearly one-quarter of the new drugs approved in Canada will eventually get a serious safety warning or have to be pulled from the market for safety reasons.3 Moreover, this ratio has increased to one-third for drugs given a priority review. Because we do have specific evidence for interactions between some medications and grapefruit, the public should be updated about new drugs where this interaction may be missed.

Is it sufficient that we identify these warnings and withdrawals only after they may have caused human suffering? After 20 years and hundreds of research publications on the topic of grapefruit–drug interaction, is there not enough well-documented science to predict with high likelihood the adverse effects and toxicity before unnecessary exposure? Our considered contention is that this is indeed the case. Moreover, a recent editorial in BMJ has lent further credence to the relevance of our conclusions.4

Even if the incidence of serious toxicity from a grapefruit–drug interaction was low in the patient population, which is as yet not fully known, the consequences would be dire (yet easily prevented). Moreover, why would you knowingly or even theoretically put yourself or others in harm’s way? Caution is by far the wisest approach.


1. Greenblatt DJ, Derendorf H. Grapefruit–medication interactions [letter]. CMAJ 2013;185: 507. [PMC free article] [PubMed]
2. Bailey DG, Dresser G, Arnold JMO. Grapefruit-medication interactions: Forbidden fruit or avoidable consequences? CMAJ 2013;185-309–16 [PMC free article] [PubMed]
3. Lexchin J. New drugs and safety: what happened to new active substances approved in canada between 1995 and 2010? Arch Intern Med 2012; October 8:1–2 [PubMed]
4. Pirmohamed M. Drug–grapefruit juice interactions. BMJ 2013;346:f1. [PubMed]

Articles from CMAJ : Canadian Medical Association Journal are provided here courtesy of Canadian Medical Association