4-Phenylpropylphenethylamine (4-PhPr-PEA or 4-PPPEA), is a serotonin receptor modulator of the phenethylamine family related to phenethylamine (PEA). It is the 4-(3-phenylpropyl) derivative of phenethylamine. The drug shows relatively high affinity for the serotonin 5-HT<sub>2A</sub> and 5-HT<sub>2C</sub> receptors (K<sub>i</sub> = 60nM and 525nM, respectively). Its affinity for the serotonin 5-HT<sub>2A</sub> receptor was 280-fold higher than that of phenethylamine (which was K<sub>i</sub> = 16,800nM). 4-PhPr-PEA was not specifically assessed itself, but analogues were tested, and based on the results with them, the drug is assumed to act as an antagonist or low-efficacy partial agonist of the serotonin 5-HT<sub>2A</sub> receptor. 4-PhPr-PEA is notable as it indicates that methoxy groups on the phenyl ring are not required for high affinity binding to serotonin receptors, though they do appear to be required for efficacious agonism. The drug was first described in the scientific literature by Richard Glennon and colleagues in 2000.