Dopamine, a sympathomimetic amine vasopressor, is the naturally occurring immediate precursor of norepinephrine. G protein-coupled dopamine receptors (D1, D2, D3, D4, and D5) mediate all of the physiological functions of the catecholaminergic neurotransmitter dopamine, ranging from voluntary movement and reward to hormonal regulation and hypertension. Dopamine HCl is indicated for the correction of hemodynamic imbalances present in the shock syndrome due to myocardial infarction, trauma, endotoxic septicemia, open-heart surgery, renal failure, and chronic cardiac decompensation as in congestive failure.

Levodopa (L-DOPA) was first isolated from seedlings of Vicia faba by Marcus Guggenheim in 1913. Levodopa, a dopamine precursor, is an effective and well-tolerated dopamine replacement agent used to treat Parkinson's disease. Oral levodopa has been widely used for over 40 years, often in combination with a dopa-decarboxylase inhibitor carbidopa, which reduces many treatment complications, extending its half-life and increasing levodopa availability to the brain. Entacapone, a catechol-O-methyltransferase inhibitor, can also be used to improve the bioavailability of levodopa, especially when used in conjunction with a carbidopa.

Piclozotan (SUN N4057) is a 1,4-benzoxazepine derivative that exhibits sub-nanomolar affinity at serotonin 1A receptor with good selectivity over dopamine D2 and α1-adrenoceptors. Piclozotan reduced levodopa-induced forelimb hyperkinesia by 55% and 69%, respectively, at 1h relative to the control. Piclozotan significantly lengthened the duration of rotational behavior by 26% versus the control and attenuated the increase in striatal levodopa-derived extracellular dopamine levels. Piclozotan, a serotonin 1A agonist, can improve motor complications in patients with advanced Parkinson's disease. Piclozotan has been shown to be neuroprotective against ischemic neuronal damage in animal models. Piclozotan had been in phase II for the treatment of stroke. However, this research has been discontinued.

3-O-methyldopa (3-OMD) is a metabolite of L-3,4-dihydroxyphenylalanine (L-DOPA), a drug used for the treatment of Parkinson's disease patients. 3-OMD is formed by catechol-O-methyltransferase. 3-OMD may be responsible for the side effects of L-DOPA.