Α5IA

α₅IA (LS-193,268) is a nootropic drug invented in 2004 by a team working for Merck, Sharp and Dohme, which acts as a subtype-selective inverse agonist at the benzodiazepine binding site on the GABA_A receptor. It binds to the α₁, α₂, α₃ and α₅ subtypes, but shows much higher efficacy at the α₅ subtype, and acts either as a weak partial agonist or inverse agonist at the other subtypes, with its partial agonist effect at α₂ likely to be responsible for the lack of anxiety produced by this drug when compared to older α₅-preferring inverse agonists such as L-655,708.

The α₅ subtype is expressed predominantly in the hippocampus, an area of the brain involved with learning and memory, and activation of this subtype is thought to be largely responsible for producing the cognitive side effects displayed by many benzodiazepine and nonbenzodiazepine drugs, such as amnesia and difficulties with learning and memory. This led researchers to conclude that a drug acting as an inverse agonist at this subtype should have the opposite effect and enhance learning and memory.

Older non-selective inverse agonists at the benzodiazepine site such as DMCM are associated with a range of other effects including anxiety and convulsions, but because α₅IA acts specifically at the α₅ subtype it produces nootropic effects in animal studies, yet without any significant anxiogenic or pro-convulsant effects. This gives α₅IA the potential to be a useful drug either to be used alongside benzodiazepines to counteract their cognitive side effects, or by itself as a nootropic with possible applications in the treatment of Alzheimer's disease and other forms of dementia.