Befiradol is a very potent and highly selective 5-HT1A receptor full agonist. A SAR study revealed that replacement of the dihalophenyl moiety by 3-benzothienyl increases maximal efficacy from 84% to 124%. In recombinant cell lines expressing human 5-HT1A receptors, befiradol exhibits high agonist efficacy for a variety of signal transduction read-outs, including ERK phosphorylation, G-protein activation, receptor internalization and adenylyl cyclase inhibition. In rat hippocampal membranes it preferentially activates GalphaO proteins. In neurochemical experiments, befiradol activated 5-HT1A autoreceptors in rat dorsal Raphe nucleus as well as 5-HT1A heteroreceptors on pyramidal neurons in the frontal cortex. It has powerful analgesic and antiallodynic effects comparable to those of high doses of opioid painkillers, but with fewer and less prominent side effects, as well as little or no development of tolerance with repeated use.