sentences:  At least 36 species of the genus "Heracleum" in the family Apiaceae are known to contain one or more furanocoumarin compounds.Furanocoumarins have other biological effects as well.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.