Hordenine is a natural Phenethylamine compound that occurs in a number of different plants, but especially barley grass. It is structurally similar to the amino acid Tyramine. It antagonized D2-mediated beta-arrestin recruitment indicating functional selectivity. Hordenine inhibited melanogenesis by suppressing cAMP production, which is involved in the expression of melanogenesis-related proteins. Hordenine may be an effective inhibitor of hyperpigmentation. Hordenine is an indirectly acting adrenergic drug. It liberates norepinephrine from stores. In isolated organs and those structures with reduced epinephrine contents, the hordenine-effect is only very poor. Experiments in intact animals (rats, dogs) show that hordenine has a positive inotropic effect upon the heart, increases systolic and diastolic blood pressure, peripheral blood flow volume, inhibits gut movements but has no effect upon the psychomotorical behavior of mice. Hordenine is considered to be generally very safe and well-tolerated in healthy adults. Hordenine is a nootropic compound that works equally well for cognitive enhancement and athletic performance.

Propylnorapomorphine is a potent and selective D2 receptor agonist. Propylnorapomorphine is used as a tool compound to label dopamine receptors in rodent brain, and elicits dopaminergic behavioural effects. It stimulates motor activity, induces stereotypic behaviour and sexual stimulation. Propylnorapomorphine was investigated in clinical trial against Parkinson's disease and schizophrenia

Pergolide is a long-acting dopamine agonist approved in 1982 for the treatment of Parkinson’s Disease. It is an ergot derivative that acts on the dopamine D2 and D3, alpha2- and alpha1-adrenergic, and 5-hydroxytryptamine (5-HT) receptors. It was indicated as adjunct therapy with levodopa/carbidopa in the symptomatic treatment of parkinsonian syndrome. It was later found that pergolide increased the risk of cardiac valvulopathy. The drug was withdrawn from the US market in March 2007 and from the Canadian market in August 2007. Pergolide stimulates centrally-located dopaminergic receptors resulting in a number of pharmacologic effects. Five dopamine receptor types from two dopaminergic subfamilies have been identified. The dopaminergic D1 receptor subfamily consists of D1 and D5 subreceptors and are associated with dyskinesias. The dopaminergic D2 receptor subfamily consists of D2, D3 and D4 subreceptors and has been associated with improvement of symptoms of movement disorders. Thus, agonist activity specific for D2 subfamily receptors, primarily D2 and D3 receptor subtypes, are the primary targets of dopaminergic antiparkinsonian agents. It is thought that postsynaptic D2 stimulation is primarily responsible for the antiparkinsonian effect of dopamine agonists, while presynaptic D2 stimulation confers neuroprotective effects. This semisynthetic ergot derivative exhibits potent agonist activity on dopamine D2- and D3-receptors. It also exhibits agonist activity on dopamine D4, D1, and D5, 5-hydroxytryptamine (5-HT)1A, 5-HT1B, 5-HT1D, 5-HT2A, 5-HT2B, 5-HT2C, α2A-, α2B-, α2C-, α1A-, α1B-, and α1D-adrenergic receptors. Parkinsonian Syndrome manifests when approximately 80% of dopaminergic activity in the nigrostriatal pathway of the brain is lost. As this striatum is involved in modulating the intensity of coordinated muscle activity (e.g. movement, balance, walking), loss of activity may result in dystonia (acute muscle contraction), Parkinsonism (including symptoms of bradykinesia, tremor, rigidity, and flattened affect), akathesia (inner restlessness), tardive dyskinesia (involuntary muscle movements usually associated with long-term loss of dopaminergic activity), and neuroleptic malignant syndrome, which manifests when complete blockage of nigrostriatal dopamine occurs. High dopaminergic activity in the mesolimbic pathway of the brain causes hallucinations and delusions; these side effects of dopamine agonists are manifestations seen in patients with schizophrenia who have overractivity in this area of the brain. The hallucinogenic side effects of dopamine agonists may also be due to 5-HT2A agonism. The tuberoinfundibular pathway of the brain originates in the hypothalamus and terminates in the pituitary gland. In this pathway, dopamine inhibits lactotrophs in anterior pituitary from secreting prolactin. Increased dopaminergic activity in the tuberoinfundibular pathway inhibits prolactin secretion. Pergolide also causes transient increases in somatotropin (growth hormone) secretion and decreases in luteinizing hormone (LH) concentrations. Pergolide is not available for use by humans in the United States, but approved for veterinary use; it was used in various other countries for the treatment of various conditions including Parkinson's disease, hyperprolactinemia, and restless leg syndrome. Pergolide in Europe was indicated for Parkinson's disease only when other dopaminergic agonist treatments had failed, and treatment had to be initiated by a neurologist. The label warned against using doses of more than 5mg a day, whether alone or in combination with levodopa. However the marketing of this drug finally stopped in France in May 2011 and sales elsewhere in Europe ceased eventually.

Benzquinamide also known as BZQ; Emete-con, Emetico, is an antiemetic drug, which was discontinued. That drug was used to prevent and treat nausea and vomiting associated with anesthesia and surgery, administered intramuscularly or intravenously. The mechanism of action is not known, but was made predictions which shown, that in spite of benzquinamide did bind to the α2A, α2B, and α2C adrenergic receptors (α2-AR). It was known, that this activity may partially explain the anxiolytic activity effect of the drug. But the dopamine D2 receptor, which by ligand-set similarity resembles α2-AR is an accepted target for emesis. Then benzquinamide was tested towards to the D2, D3, and D4 receptors. Notwithstanding the fact that the α2-AR values are lower than the D2 values, it was predicted, that D2 activity may be the most relevant for emesis.

Carfenazine (brand name Proketazine) is an antipsychotic and tranquilizer of the phenothiazine group. It is used in the treatment of acute or chronic schizophrenic reactions in hospitalized patients. Proketazine blocks postsynaptic mesolimbic dopaminergic D1 and D2 receptors in the brain; depresses the release of hypothalamic and hypophyseal hormones and is believed to depress the reticular activating system thus affecting basal metabolism, body temperature, wakefulness, vasomotor tone, and emesis. The following is a list of possible side effects that may occur from all constituting ingredients of Proketazine: akathisia, tardive dyskinesia, extrapyramidal symptoms, allergic purpura.

Acetophenazine (Tindal) is an antipsychotic drug of moderate-potency. Used in the treatment of disorganized and psychotic thinking. Acetophenazine (Tindal) is also used to help treat false perceptions (e.g. hallucinations or delusions). Acetophenazine acts as an antagonist of dopaminergic D2 receptors in the brain. Acetophenazine exhibited modest androgen receptor binding and antiandrogen activity.

PROTHIPENDYL is a neuroleptic azaphenothiazine used to treat anxiety and agitation in psychotic syndromes. It also shows strong antihistamine and anti-emetic actions.

PROTHIPENDYL is a neuroleptic azaphenothiazine used to treat anxiety and agitation in psychotic syndromes. It also shows strong antihistamine and anti-emetic actions.

PROTHIPENDYL is a neuroleptic azaphenothiazine used to treat anxiety and agitation in psychotic syndromes. It also shows strong antihistamine and anti-emetic actions.

Triflupromazine is antipsychotic and an antiemetic drug (sold under the brand names VESPRIN) which used to management of psychoses. However, this drug was discontinued. Triflupromazine binds to the dopamine D1 and dopamine D2 receptors and inhibits their activity. Moreover, binds the muscarinic acetylcholine receptors (M1 and M2).