Glycine (Cly) is a natural amino acid neurotransmitter that acts as a co-agonist at Glutamate [NMDA] receptors in the brain and is an activator of glycine receptors, GLRA1-3, GLRB. The abnormal Gly levels have been implicated in neuropsychiatric disorders. Alterations in Gly levels are implicated in several diseases of the central nervous system. Glycine was studied in phase II of clinical trials in patients with schizophrenia. The results have shown that using of glycine was associated with reduced symptoms with promising effect sizes and a possibility of improvement in cognitive function. Besides, glycine was also studied in clinical trials phase II in children with cystic fibrosis. The clinical, spirometric and inflammatory status of subjects with cystic fibrosis improved after just 8 weeks of glycine intake, suggesting that this amino acid might constitute a novel therapeutic tool for these patients. In addition, Gly was proposed as a biomarker for brain tumor malignancy. Glycine is a component of a nutrients mixture for peripheral administration to well-nourished mildly catabolic adult patients who require only short-term parenteral nutrition.

Tetrahydropalmatine is a tetrahydroprotoberberine isoquinoline alkaloid that is a primary active constituent of herbal preparations containing plant species of the genera Stephania and Corydalis. The levo isomer of THP (L-THP) appears to contribute to many of the therapeutic effects of these preparations. The pharmacological profile of L-THP, which includes antagonism of dopamine D1 and D2 receptors and actions at dopamine D3, suggests that it may have utility for treating addiction. Clinical trials where L-THP was used for the treatment of cocaine and heroin addiction have promising results. The clinical trial is planned for the treatment of schizophrenia. L-Tetrahydropalmatine is recorded in the Chinese pharmacopoeia.

CYR-101 (MIN-101) is a cyclic amide derivative that has high equipotent affinities for 5-HT2A and sigma-2 receptors (Ki of 7.53 nM and 8.19 nM for 5-HT2A and sigma-2, respectively). MIN-101 also shows binding affinity for a1-adrenergic receptors but low or no affinity for muscarinic, cholinergic, and histaminergic receptors. MIN-101 demonstrated statistically significant efficacy in reducing negative symptoms and good tolerability in stable schizophrenia patients. The drug is in phase II clinical trials for the treatment of Schizophrenia.

JNJ-37822681 is a novel, potent, specific, centrally active, dopamine D2 receptor antagonist, which was developed by Johnson & Johnson. This drug is in the phase II of clinical trial for the treatment of schizophrenia. JNJ-37822681 has optimal brain disposition and somnolence was the most frequently reported adverse effect.

JNJ-37822681 is a novel, potent, specific, centrally active, dopamine D2 receptor antagonist, which was developed by Johnson & Johnson. This drug is in the phase II of clinical trial for the treatment of schizophrenia. JNJ-37822681 has optimal brain disposition and somnolence was the most frequently reported adverse effect.

Encenicline (EVP-6124; MT-4666) acts as a potent partial and selective agonist at alpha-7 nicotinic acetylcholine receptor. Encenicline significantly improved memory function in animal models. FORUM Pharmaceuticals (formerly EnVivo Pharmaceuticals) is developing encenicline for the treatment of cognition disorders such as schizophrenia and for Alzheimer's disease.

Idazoxan is an alpha2 receptor antagonist which also shows activity at imidazoline I1 and I2 receptors and modulates the release of dopamine. Idazoxan was in phase II development in the US. Later the development of idazoxan for schizophrenia was discontinued. It was also in clinical trials for cognition disorders in United Kingdom, and was also discontinued. Idazoxan is used in scientific research as a tool for the study of alpha 2-adrenoceptors.

Clorotepine (aka octoclothepin or octoclothepine) is an antipsychotic from the tricyclic group derived from perathiepin. It was originally developed in 1965 and marketed in the Czech Republic by Spofa in or around 1971 for the treatment of schizophrenic psychosis. Clorotepine has a high affinity for the dopamine (D1, D2, D3, D4), receptors the serotonin 5-HT (2A, 2B, 2C, 6, 7) receptors, the alpha-adrenergic receptors (1A, 1B, 1D), and the histamine H1 receptors. In most instances, it acts as an antagonist (or inverse agonist). Clorotepine will also block the reuptake of norepinephrine by inhibiting the norepinephrine transporter.

Idalopirdine (Lu AE58054) is a Serotonin 6 receptor (5-HT6) antagonist. Idalopirdine exrets good oral bioavailability and robust efficacy in a rat model of cognitive impairment in schizophrenia. In rats idalopirdine potentiates the effects of acetylcholinesterase inhibitor donepezil on two pharmacodynamic biomarkers associated with cognition, i.e. neuronal oscillations and extracellular ACh levels in the hippocampus. Such potentiation could contribute to the procognitive effects of idalopirdine observed in donepezil-treated Alzheimer's disease patients. The compound is being developed by Lundbeck as an adjunctive therapy with acetylcholinesterase inhibitor donepezil, and is in phase III development for the treatment of Alzheimer's disease in multiple countries worldwide. A phase II trial for the treatment of cognitive impairment associated with schizophrenia was conducted; however no recent reports of development for idalopirdine have been identified.

Adoprazine (SVL-313) is a full 5-HT1A receptor agonist and full D2/3 receptor antagonist possessing characteristics of an atypical antipsychotic, representing a potential novel treatment for schizophrenia and bipolar disorder. This drug together with some others, e.g. Mazapertine succinate, PF-217830 was discontinued from clinical trials due to either non-optimal pharmacokinetic properties or insufficient therapeutical efficacy.