Monocrotaline is an 11-membered macrocyclic pyrrolizidine alkaloid extracted from the seeds of Crotalaria plants. It inhibits organic cation transporters OCT-1 and OCT-2, with IC50 values of 36.8 µM and 1.8 mM, respectively. Monocrotaline exhibits antitumor activity and shows certain cytotoxicity against liver cancer cells such as HepG2. It is also commonly used to induce pulmonary arterial hypertension models in rodents.