2-Iodo-LSD (IOL) is a putatively non-hallucinogenic serotonin receptor modulator of the lysergamide family related to 2-bromo-LSD (BOL-148) and lysergic acid diethylamide (LSD). It is the 2-iodo derivative of LSD.
According to Alexander Shulgin in his 1997 book TiHKAL (Tryptamines I Have Known and Loved), it is unknown whether 2-iodo-LSD has ever been tested in humans.
2-Iodo-LSD shows high affinity for the serotonin 5-HT<sub>2</sub> receptors and also shows affinity for other serotonin receptors as well as for the dopamine and adrenergic receptors. In contrast to LSD, but similarly to 2-bromo-LSD, 2-iodo-LSD is predominantly antagonistic at the serotonin 5-HT<sub>2A</sub> and 5-HT<sub>2C</sub> receptors and is described as non-hallucinogenic. The drug has about 57.4% of the antiserotonergic activity of LSD in the isolated rat uterus in vitro, whereas 2-bromo-LSD has about 103% of LSD's potency in this assay.
[<sup>125</sup>I]2-Iodo-LSD, a radiolabeled analogue of 2-iodo-LSD, has been used as a radioligand for serotonin 5-HT<sub>2</sub> receptors. In addition, radiolabeled derivatives of 2-iodo-LSD, such as 1-methyl-2-[<sup>125</sup>I]iodo-LSD ([<sup>125</sup>I]-MIL) and 1-ethyl-2-[<sup>125</sup>I]iodo-LSD ([<sup>125</sup>I]-EIL), have been developed for use as presumably non-hallucinogenic agents in imaging of serotonin receptors.
2-Iodo-LSD was described in the scientific literature by Albert Hofmann and colleagues by 1956.