Parafluorophenylpiperazine (flippiperazine, fluoperazine, pFPP, 4FPP) is a piperazine derivative with mildly hallucinogenic and euphoric effects which has been sold as an ingredient in legal recreational drugs known as "Party pills", initially in New Zealand and subsequently in other countries around the world.

pFPP has been found in vitro to act mainly as a 5HT1A serotonin receptor agonist, with some affinity for 5HT2A and 5HT2C receptors. It also inhibits the reuptake of serotonin and noradrenaline. pFPP was originally discovered as a metabolite of the hypnotic antihistamine Niaprazine in 1982, but was subsequently re-discovered in 2003 as a potential recreational drug, and subsequently sold as an ingredient in "Party pills" in New Zealand, under brand names such as "The Big Grin" and "Mashed".

pFPP has little stimulant effects, with its subjective effects derived mainly from its action as a 5HT1A agonist. Its effects have been described as similar to a cross between Prozac and LSD, both of which have significant actions as 5HT1A agonists in addition to their primary mechanism of action. pFPP is active at doses between 20mg - 150mg, but higher doses cause a range of side effects including migraine headaches, muscle aches, nausea and vomiting, which tend to discourage abuse.