5-I-R91150 (or R93274) is a compound that acts as a potent and selective antagonist of 5-HT<sub>2A</sub> receptors. Its main application is as its iodine-123 radiolabeled form, in which it can be used in SPECT scanning in human neuroimaging studies, to examine the distribution of the 5-HT<sub>2A</sub> receptor subtype in the brain, e.g. with respect to sex and age and in adults with Asperger syndrome or Alzheimer's disease.
An alternative 5-HT<sub>2A</sub> receptor ligand also used in neuroimaging is altanserin.