Lysergine, also known as 9,10-didehydro-6,8ò-dimethylergoline, is an ergot alkaloid and serotonin receptor agonist of the ergoline family. It is a minor constituent of ergot.
Lysergine shows selectivity for activation of the serotonin 5-HT<sub>2A</sub> receptor over several other closely related serotonin receptors (54-fold over the 5-HT<sub>2B</sub> receptor, 38-fold over the 5-HT<sub>2C</sub> receptor, and 127-fold over the 5-HT<sub>1A</sub> receptor). The drug is a partial agonist of the 5-HT<sub>2A</sub> receptor with moderate intrinsic activity (E<sub>max</sub> = 57%).
An analogue of lysergine, (+)-13-fluorolysergol, is an even more selective agonist of the 5-HT<sub>2A</sub> receptor than lysergine (EC<sub>50</sub> for 5-HT<sub>2B</sub> and 5-HT<sub>2C</sub> of >10,000nM). However, this compound has relatively weak maximal efficacy in activating the receptor (E<sub>max</sub> = 17%).