Grapefruit Is One of the Weirdest Fruits on the Planet

Grapefruit has a high volume of compounds called furanocoumarins, which are designed to protect the fruit from fungal infections. When you ingest grapefruit, those furanocoumarins take your cytochrome P450 enzymes offline. There’s no coming back. Grapefruit is powerful, and those cytochromes are donezo. So the body, when it encounters grapefruit, basically sighs, throws up its hands, and starts producing entirely new sets of cytochrome P450s. This can take over 12 hours.

This rather suddenly takes away one of the body’s main defense mechanisms. If you have a drug with 10 percent bioavailability, for example, the drugmakers, assuming you have intact cytochrome P450s, will prescribe you 10 times the amount of the drug you actually need, because so little will actually make it to your bloodstream. But in the presence of grapefruit, without those cytochrome P450s, you’re not getting 10 percent of that drug. You’re getting 100 percent. You’re overdosing.

And it does not take an excessive amount of grapefruit juice to have this effect: Less than a single cup can be enough, and the effect doesn’t seem to change as long as you hit that minimum.

None of this is a mystery, at this point, and it’s shockingly common. Here’s a brief and incomplete list of some of the medications that research indicates get screwed up by grapefruit:

Benzodiazepines (Xanax, Klonopin, and Valium) Amphetamines (Adderall and Ritalin) Anti-anxiety SSRIs (Zoloft and Paxil) Cholesterol-lowering statins (Lipitor and Crestor) Erectile-dysfunction drugs (Cialis and Viagra) Various over-the-counter meds (Tylenol, Allegra, and Prilosec) And about a hundred others.

Some drugs get cleared from your bloodstream by an enzyme grapefruit disables, so build up when you eat grapefruit. Others depend on that enzyme to be converted to their active form, so grapefruit keeps them inactive. Your pharmacist is probably better at identifying stuff like that than your doctor.

Once I was traveling, and left my meds behind. Eating grapefruit twice a day maintained drug levels in my bloodstream while I worked out an alternative supply. This is very uncertain business.

Lemon and lime also have the stuff grapefruit has. So, pigging out on lemon bars can be as dangerous as eating grapefruit, if it is.

According to Wikipedia cytochrome P450 is also responsible for hormonal regulation (including testosterone and estrogen), cholesterol synthesis, and the filtering of more natural toxins (this is the mechanism relavent to most medications). I really want to see a long term study of regular grapefruit consumption (absent drugs) now since those are pretty big things to be regularly disrupted.

https://en.m.wikipedia.org/wiki/Cytochrome_P450

Glass of grape juice and that viagra tablet will do wonders for grandpa

Think of all those super-expensive (in the US) drugs that are mediated by Cytochrome P450. If only they would say “take one tenth of the $250-per-pill dose plus a 50¢ glass of grapefruit juice.”

Previous discussion: https://news.ycombinator.com/item?id=24705855

Hate to admit this but when I was opioid dependent I would eat copious amount of grapefruits to make the pills more potent. I could never tell the difference

Are there other foods with similar effects?

I'm heavily concerned that this is a possible factor behind the stories mentioned at ritalindeath. It makes me sad that those grieving parents end up promoting crap like homeopathy for "treating" ADHD as an alternative method.

Grapefruit tastes like medicine.

My favorite weirdest fruit story is the Aziz Ansari skit on 50 cent and grapefruit (or grape fruit):

https://www.youtube.com/watch?v=waCF81HdKAA