What is it about grapefruit specifically that messes with pretty much every prescription in existence?
In:
When companies that develop medications calculate their dosages, one of the major things they have to take into account is bioavailability—how much of the drug actually ends up in your bloodstream after going through your digestive system.
The cytochrome P450 group of enzymes in your digestive system is a major factor in drug bioavailability. Grapefruits, for their part, contain a *lot* of furanocoumarins, which they use to protect themselves from fungus. When furanocoumarins meet cytochrome P450 enzymes, they *completely* wipe them out, and it can take your body upwards of *12 hours* to produce an entirely new batch.
So if you ingest a medication in that window of 12+ hours where those enzymes are nonfunctional, its bioavailability may end up being *many times* what the dosage was based off of. If, for example, the company developing the drug determined that it had *10% bioavailability* after digestion specifically due to cytochrome P450 enzymes, taking it with or in a huge window after eating grapefruit or drinking grapefruit juice will result instead in *100% bioavailability*—the equivalent of having taken a dose ***ten times larger***.
The Atlas Obscura article “[Grapefruit Is One of the Weirdest Fruits on the Planet](https://www.atlasobscura.com/articles/grapefruit-history-and-drug-interactions)” has more information on the process I’ve summarized here, as well as some fascinating details on the history of the fruit itself.
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