Protopine is an isoquinoline alkaloid originally found in a variety of sources, including species of Corydalis and Papavera. Protopine exhibits analgesic, anti-inflammatory, anticancer, antioxidative, neuroprotective, and anti-parasitic/anti-helminthic activities. Protopine induces analgesia in animal models of mechanical and thermal pain; this mechanism may involve opioid, α-adrenergic, and Ca2+ signaling pathways. Protopine suppresses Ca2+ influx through inhibition of voltage-gated and receptor-gated Ca2+ channels, preventing aortic contraction. In vitro, protopine decreases levels of NO, COX-2, prostaglandin E2 (PGE2) induced by lipopolysaccharide (LPS). Additionally, protopine inhibits phosphorylation of MAPKs and activation of NF-κB. Protopine may act as a microtubule stabilizer, inhibiting depolymerization. This compound also increases activity of CDK1 and cyclin B1 and decreases levels of MCl-1, inducing apoptosis in prostate cancer cells. In PC-12 neurons, protopine increases activity of superoxide dismutase (SOD), glutathione peroxidase, and catalase, and decreases levels of malondialdehyde and caspase 3; this reduces disruption of mitochondrial membrane potential and apoptosis, increasing cell survival. Protopine also exhibits anti-parasitic activity against species of Dactylogyrus.