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My andrologist prescribed me Cialis and Cistonorm.
While reading Cialis leaflet I have discovered that grapefruit juice might affect how Cialis work and Cistonorm contains grapefruit seeds.

I know that seeds and juice are not the same thing, my doctor hasn't warned me about any issue that i might have and i have found that Cialis and Cistonorm are sometimes prescribed together, but still i'd like to have a specific answer and i have found nothing on the internet about grapefruit seeds and Cialis specifically.
So, can grapefruit seeds adversely affect Cialis the same way grapefruit juice does?

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Your question took me a while to research; it goes beyond basic medicine and delves into biochemistry, pharmacology, and physiology. The short answer is: Yes! It can; however, as you will see in the studies that are linked, it's dose dependent. From what I found, the primary culprit of drug interactions in grapefruit juice lies in naringenin; however, other compounds play a role as well. Naringenin is a natural compound (a flavonoid) found in fruits such as grapefruit, oranges, and tomatoes. The concentration of naringenin can be viewed in the following studies.

For general information on Grapefruit and it's drug interactions, you will find this article useful.

Unfortunately, I could not find a "critical level" that would cause increased drug interactions. In light of all the studies reviewed, the best course of action would be to avoid grapefruit in any form - juice, seed, or otherwise - in order to prevent any drug interaction. I hope this answers your question.

  • Yes it does answer the question, thanks. I was drinking Cistonorm in the evening while taking Cialis in the morning, after about 12 hours, in order to take them as far as possible from each other. But since Cistonorm is a temporary medication (while waiting for test results after which my andrologist will much likely prescribe me an antibiotic) i think i'll just stop taking it – valepu Aug 4 '15 at 10:17

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