2C-B-PYR, also known as 3-(4-bromo-2,5-dimethoxyphenyl)pyrrolidine, is a serotonin receptor modulator of the phenethylamine family. It is a cyclized phenethylamine, more specifically a cyclized pyrrolidine derivative of the psychedelic drug 2C-B, and is closely related to ZC-B (azetidine) and 2C-B-3PIP (piperidine). The drug acts as a potent and efficacious agonist of the serotonin 5-HT<sub>2A</sub> and 5-HT<sub>2C</sub> receptors. It was patented by Lophora in 2021 and was first described in the scientific literature in 2024.