The investigational psychopharmacologic drug candidate CP 615003 (NGD 91-3) is a potent subtype-selective partial agonist at the GABA-A receptor complex. It was designed to be fast acting without causing the sedation, memory impairment, addiction or potentiation of effects of alcohol associated with conventional anti-anxiety medication. Tissue distribution studies conducted during early clinical development of CP 615003 suggested limited brain penetration. In the Phase II clinical study, subjects tested at the high dose of NGD 91-3 showed a trend toward efficacy that did not achieve statistical significance.

L-822179 is a triazolophthalazine that selectively attenuates the effects of GABA at GABA(A) receptors containing an alpha5 subunit. It is an orally active, functionally selective compound, which enhances cognition in animals without anxiogenic or convulsant effects. The dose-limiting adverse event of L-822179 is dizziness and/or light-headedness. L-822179 does not improve cognitive performance in the elderly; indeed the dose of 4 mg actually significantly impairs performance. In this regard, it could therefore be considered that this study is a failed trial in so far as the positive control, lorazepam, does not show the anticipated effect.

PNU-142633 is selective 5HT1D partial agonist, developed by Pharmacia & Upjohn, Inc. It failed in phase II clinical trials against acute migraine, and its development was discontinued.

BMS-442606 is an S-enantiomer of 6-hydroxybuspirone and is a 5-HT1A partial agonist. BMS-442606 has advantage of being cleared more slowly from blood compared to the R-enantiomer, but R form showed higher affinity and selectivity for the 5HT1A receptor compared to the S-isomer. Because both isomers together with racemic form were well tolerated and was not found any advantage of one of the enantiomers of over the racemic form. Finally, racemic form was chosen for further clinical development.