Piperine gives black pepper its sharp bite. On its own it does not offer a direct health effect. It is added to supplements to boost how much of the other ingredients your body can use. A common example is pairing it with curcumin.
Piperine slows certain liver enzymes and transport proteins, particularly CYP3A4 and P-glycoprotein. Slowing these pathways lets more of a substance stay in your bloodstream instead of being cleared quickly. You find it in small amounts inside combination formulas, not sold alone.
Follow the label of the product you are using. The piperine dose is tiny compared to the main ingredient.
Caution is needed if you take prescription drugs. Piperine can raise blood levels of medications processed by CYP3A4 or P-glycoprotein. Such drugs include some statins, blood pressure treatments, immunosuppressants, and certain cancer therapies. Speak with your doctor before adding it. Do not use several piperine-containing products at once since combined effects are not well studied. Safety in pregnancy or while breastfeeding is unknown.