A grapefruit in the oven – does grapefruit juice negate the contraceptive pill?

The oral contraceptive pill consists of the synthetic hormones ethinyloestradiol (EE) and progestogen. It works by fooling a women’s body into thinking she’s pregnant – thus preventing further conception.

Grapefruit juice is one of the more commonly consumed fruit juices. For example 21% of US households purchase the juice regularly.

Grapefruit juice is broken down in the liver by one particular enzyme system (cytochrome P-450 3A4). This is the same enzyme system which breaks down estradiol (and other drugs). By utilising this system and “overloading” it, grapefruit juice can slow the breakdown of drugs such as estradiol. This could potentially elevate blood estradiol levels.

In a test-tube, reduced breakdown certainly occurs. Similarly in women lacking ovaries, grapefruit juice taken with oral hormones increased the level of estradiol in the blood.

So grapefruit juice interracts with oral hormones. But can this cause the failure of the contraceptive pill and unwanted pregnancies?

The jury is out on this. There appear to have been no known pregnancies as a result of grapefruit juice interraction with the pill. Furthermore, studies have used large quantities (several glasses worth) of grapefruit juice. Chances are then, that one or less glasses a day are probably fine.


Kane G.C., Lipsky J.J. (2000) Drug–Grapefruit Juice Interactions, Mayo Clin Proc. 75:933-942

Schubert W, Cullberg G, Edgar B, Hedner T (1994) Inhibition of 17 beta-estradiol metabolism by grapefruit juice in ovariectomized women. Maturitas, 155–63.

Schubert W, Eriksson U, Edgar B, Cullberg G, Hedner T, (1995) Flavonoids in grapefruit juice inhibit the in vitro hepatic metabolism of 17 beta-estradiol. Eur J Drug Metab Pharmacokinet 1995;3:219–24.

Weber A, Jager R, Borner A, Klinger G, Vollanth R, Matthey K, Balogh A (1996) Can grapefruit juice influence ethinylestradiol bioavailability? Contraception, 53:41–7.



Filed under Kitchen Science, Science

5 responses to “A grapefruit in the oven – does grapefruit juice negate the contraceptive pill?

  1. Ian

    I did a radio feature on this a few years ago! Because grapefruit interferes with cytochrome P-450, it can also interfere with many other medications. There are a few cases on record of it being life-threatening for a heart patient.

    Of course if you were drinking or eating grapefruit when your drug dose was safely established by your doctor, then suddenly stopping the grapefruit will also upset the level of pharameceuticals in your body, with potentially nasty effects.

    My podcast for this is at http://feeds.feedburner.com/~r/HeresWhy/~5/30592899/Grapefruit.mp3

  2. I read about the other interactions – it’s strange how something that seems so benign can have such effects. It makes me wonder what other foods we regularly consume that we never think to tell our doctor about (Oh, by the way doctor, I just bought a litre of milk). I particularly picked the pill out as I know that in New Zealand doctors have been advising against grapefruit juice with oral contraceptives but I had never heard of anyone being warned in Australia.

  3. If you want to see a reader’s feedback 🙂 , I rate this article for 4/5. Detailed info, but I have to go to that damn msn to find the missed pieces. Thanks, anyway!

  4. Hello, I just now found this site whilst browsing around online as I’m looking for some material on wall ovens!. It is a very interesting website so I bookmarked this site and I intend to come back tomorrow to allow more time for a proper read when I’m more free.

  5. Naomi

    the pill doesn’t work by making the body think it’s pregnant, it works make making the ovaries think they have already ovulated and not to do it again, so there’s no egg to be fertilised. they are two quite diffferent distinctions so good to clarify. 🙂

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