Black Pepper is a spice commonly used in many areas of the world for flavor. Through its active component Piperine, Black Pepper is able to modify supplement and drug metabolism.
A process in the liver called glucuronidation, which attaches a molecule (glucuronide) to drugs to signal for their urinary excretion, is inhibited with piperine. This process prevents excessive levels of drugs and supplements in the body, but sometimes inhibits all uptake and renders some supplements useless. In the scenario of piperine ingestion, excretion of supplements is hindered and certain drugs and supplements can bypass this regulatory stage (as not all are subject to it).
This is good in some cases, as Piperine is required to give curcumin to the extremities rather than it getting consumed by glucuronidation in the liver. However, in some other cases it can lead to elevated levels of certain drugs in the blood. Again, elevated could be good or bad depending on context; regardless, caution should be taken when approaching this compound.