Piperonyl butoxide (PBO) is a pesticide synergist. It does not, by itself have pesticidal properties. However, when added to insecticide mixtures, typically pyrethrin, pyrethroid, and carbamate insecticides, their potency is increased considerably.

Piperonyl butoxide is a potent Cytochrome P450 inhibitor. This family of enzymes act as the principal detoxification pathway for many pesticides. Inhibiting the detoxification pathway allows higher unmetabolised systemic concentrations of the active insecticide to remain within the target animal for a longer period.

Piperonyl butoxide is moderately stable, and is a semisynthetic derivative of safrole. It is a derivative of piperic acid .

It is debatable whether the substance is oncogenic, mutagenic, or teratogenic in humans. Its acute oral and dermal toxicity in mammals is low, however it is toxic to fish and potentiates rotenone.