[2] (An exception is the common fig where furanocoumarins are found chiefly in the milky sap of the leaves and shoots but not the fruits.
[5] Furanocoumarins produced by plants may serve as a defense mechanism against predators such as insects and mammals.
[8] In particular, the linear furanocoumarins (psoralen, bergapten, and methoxsalen), which occur naturally in Apiaceae, Rutaceae, and other plant families, are known to be toxic to fungi.
[10] The toxin can sometimes be found even in the most common foods, including carrots, parsley, limes, and lemons, as reported in the New England Journal of Medicine in the case of a man who manually squeezed a dozen limes and then inadvertently exposed his hand directly to the sunlight without precaution, triggering a severe phytophotodermatitis for several months.
For example, in humans, bergamottin and 6',7'-dihydroxybergamottin are responsible for the "grapefruit juice effect", in which these furanocoumarins affect certain P450 liver and gut enzymes, such as the inhibition of CYP3A4 which either activates or deactivates many drugs, thus leading to higher or lower levels in the bloodstream.