Black Pepper is a source of piperine, a molecule that does not do much on its own but can inhibit enzymes that would attack other molecules. Due to this, it is ingested alongside some supplements to increase their absorption rates and is almost always consumed with curcumin. Through its active component Piperine, Black Pepper is able to modify supplement and drug metabolism.
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The usage of black pepper extract for the purpose of enhancing the absorption of other supplements that are glucuronidated (for example, curcumin) tends to call for 20mg of the bioactive piperidine.
Piperine is known for changing metabolism of various drugs and supplements, most notably increasing curcumin bioavailability by 2000%. It affects metabolism by both intestinal absorption as well as downregulating or inhibiting phase II detoxification enzymes and the glucuronidation process in the liver. It may also contribute to increase absorption by slowing intestinal transit rate and thus prolonging the time said compounds are exposed to the potential uptake.