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.
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