Bupropion is an atypical antidepressant that also has usefulness as a smoking-cessation aid. Because hydroxybupropion, a major metabolite of bupropion, is believed to contribute to its antidepressant activity, this metabolite may also contribute to the smoking-cessation properties of bupropion. Compared to bupropion hydroxybupropion inhibit norepinephrine (NE) uptake with similar potency. The effects of bupropion and enantiomers of hydroxybupropion on human nAChR subtypes indicate that the (2S,3S) isomer is more potent than the (2S,3R) isomer or racemic bupropion as an antagonist of alpha(4)beta(2) subtypes of nicotinic acetylcholine receptor (nAChR). In addition, both isomers of hydroxybupropion possess weaker antagonist activity to the alpha3/beta4 and alpha4/beta4 subtypes of nAChR.

Naltrindole is a highly potent, highly selective delta opioid receptor antagonist. It is predominantly used as a molecular probe in biomedical studies exploring the manipulation of delta opioid receptors. Naltrindole was shown to inhibit cancer cell growth in vitro; potentially through a nonopioid receptor-dependant mechanism.

3-(2-Carboxypiperazin-4-yl)Propyl-1-Phosphonic acid (also known as CPP) is neuro active amino acid and antagonist of the N-methyl-D-aspartate receptor (NMDA). It has been studied in rat models for memory, learning, and pain. Although it did show some efficacy in reducing pain it also appears to significantly impair working memory.

ABT-239 is a selective, nonimidazole H3 receptor antagonist/inverse agonist, which was investigated by Abbott laboratory as a potential drug for treatment of a variety of cognitive disorders including attention deficit/hyperactivity disorder, Alzheimer's disease, and schizophrenia.