Dihydroergotamine (DHE) is a semisynthetic, hydrogenated ergot alkaloid, synthesized by reducing an unsaturated bond in ergotamine. Dihydroergotamine was originally envisaged as an antihypertensive agent, but it was later shown to be highly effective in treating migraine. Dihydroergotamine was first used to treat migraine in 1945 by Horton, Peters, and Blumenthal at the Mayo Clinic. In 1986, Raskin and Callaham reconfirmed the effectiveness of DHE for both intermittent and intractable migraine. The use of DHE was reviewed by Scott in 1992. In 1997, a nasal spray version was approved for use in migraine. Dihydroergotamine is indicated for the acute treatment of migraine headaches with or without aura and the acute treatment of cluster headache episodes. Dihydroergotamine binds with high affinity to 5-HT1Dα and 5-HT1Dβ receptors. It also binds with high affinity to serotonin 5-HT1A, 5-HT2A, and 5-HT2C receptors, noradrenaline α2A, α2B and α, receptors, and dopamine D2L and D3 receptors. The therapeutic activity of dihydroergotamine in migraine is generally attributed to the agonist effect at 5-HT1D receptors. Two current theories have been proposed to explain the efficacy of 5-HT1D receptor agonists in migraine. One theory suggests that activation of 5-HT1D receptors located on intracranial blood vessels, including those on arterio-venous anastomoses, leads to vasoconstriction, which correlates with the relief of migraine headache. The alternative hypothesis suggests that activation of 5-HT1D receptors on sensory nerve endings of the trigeminal system results in the inhibition of proinflammatory neuropeptide release.

Apomorphine (brand names: Apokyn, Ixense, Spontane, Uprima) is indicated for the acute, intermittent treatment of hypomobility, “off” episodes (“end-of-dose wearing off” and unpredictable “on/off” episodes) in patients with advanced Parkinson’s disease. Apomorphine has been studied as an adjunct to other medications. It is a non-ergoline dopamine agonist with high in vitro binding affinity for the dopamine D4 receptor, and moderate affinity for the dopamine D2, D3, and D5, and adrenergic α1D, α2B, α2C receptors. The precise mechanism of action as a treatment for Parkinson’s disease is unknown, although it is believed to be due to stimulation of post-synaptic dopamine D2-type receptors within the caudate-putamen in the brain.

Apomorphine (brand names: Apokyn, Ixense, Spontane, Uprima) is indicated for the acute, intermittent treatment of hypomobility, “off” episodes (“end-of-dose wearing off” and unpredictable “on/off” episodes) in patients with advanced Parkinson’s disease. Apomorphine has been studied as an adjunct to other medications. It is a non-ergoline dopamine agonist with high in vitro binding affinity for the dopamine D4 receptor, and moderate affinity for the dopamine D2, D3, and D5, and adrenergic α1D, α2B, α2C receptors. The precise mechanism of action as a treatment for Parkinson’s disease is unknown, although it is believed to be due to stimulation of post-synaptic dopamine D2-type receptors within the caudate-putamen in the brain.

Quinelorane is an octahydropyrimido[4,5-g]quinolone derivative patented by American pharmaceutical company Eli Lilly and Co. as for the treatment anxiety, Parkinson's syndrome, depression, and hypertension. Quinelorane acts as an agonist of dopamine agonist for the D2 and D3 receptors. In preclinical studies Quinelorane (IM) treatment produced dose-dependent effects on male sexual responding. Penile erections and masturbation were markedly facilitated following treatment with either 2.5 or 5 micrograms/kg quinelorane. Higher doses of quinelorane (10 and 25 micrograms/kg) generally did not further augment sexual responding but rather resulted in a return in sexual responding to control vehicle levels. Quinelorane had a biphasic effect on yawning behavior of the monkeys with low doses (2.5 and 5 micrograms/kg) facilitating yawning and high doses (25 micrograms/kg) inhibiting yawning.

Ecopipam (SCH-39166) is a selective D1 dopamine receptor antagonist both in vitro and in vivo. Additionally, it exhibits saturable, high-affinity binding to D5 receptors. Ecopipam was studied clinically for a variety of indications, including schizophrenia, drug abuse, and obesity, but in each case undesirable effects were observed. Currently, ecopipam is in clinical trials for the treatment of Lesch-Nyhan and Gilles de la Tourette's syndromes.

Adrogolide is a chemically stable prodrug of the dopamine D1 receptor agonist A-86929. Adrogolide is rapidly converted in plasma to A-86929. A-86929 has high affinity and functional selectivity for the dopamine D1 receptor. Adrogolide has been in phase II clinical trials for the treatment of Parkinson's disease and cocaine abuse. However, this research has been discontinued. The adverse events associated with its use of adrogolide were of mild-to-moderate severity and included injection site reaction, asthenia, headache, nausea, vomiting, postural hypotension, vasodilitation, and dizziness.

Carmoxirole is a dopamine D2 receptor agonist with limited central activity that modulates sympathetic activation and subsequently reduces pre-load and afterload in animals. It was shown, that carmoxirole induced beneficial effects on hemodynamic and neurohumoral parameters in heart failure. In addition, experimental evidence showed that carmoxirole lowered blood pressure in various models of hypertension mainly or exclusively through inhibition of noradrenaline release from sympathetic nerve endings. That effect of carmoxirole was mediated by presynaptic dopamine receptors with the characteristic that release inhibition was restricted to low rates of sympathetic nerve discharge.

Adrogolide is a chemically stable prodrug of the dopamine D1 receptor agonist A-86929. Adrogolide is rapidly converted in plasma to A-86929. A-86929 has high affinity and functional selectivity for the dopamine D1 receptor. Adrogolide has been in phase II clinical trials for the treatment of Parkinson's disease and cocaine abuse. However, this research has been discontinued. The adverse events associated with its use of adrogolide were of mild-to-moderate severity and included injection site reaction, asthenia, headache, nausea, vomiting, postural hypotension, vasodilitation, and dizziness.

Sonepiprazole exhibits highly specific binding to the D4 dopamine receptor with more than 100-fold selectivity for the D4 receptor over other receptors, including dopamine, serotonin, and adrenergic receptors. It is a neutral antagonist at the D4 dopamine receptor and is devoid of dopamine agonist activity. Sonepiprazole selectively induces c-fos expression in the prefrontal cortex and blocks behavioral, biochemical, and genomic effects of repeated amphetamine administration in rats. Sonepiprazole was investigated as an antipsychotic for the treatment of schizophrenia in a placebo-controlled clinical trial, but in contrast to its comparator olanzapine no benefits were found and it was not researched further for this indication.

Aplindore (DAB-452) is a small molecule that displays potent dopamine D2 receptor partial agonist activity in in vitro and in vivo assays and is predicted to have antipsychotic efficacy without motor side effects. Aplindore had been in phase II clinical trials for the treatment of Parkinson's disease and restless legs syndrome. Aplindore was generally well tolerated and there were no withdrawals due to adverse events and no serious adverse events.