Biopterin (also known as L-erythro-biopterin or 6-Biopterin) is an oxidation product of tetrahydrobiopterin. Bioptrrin is an endogenous enzyme cofactor and its accumulation serves as markers of Parkinson's disease, Hyperphenylalaninemia and in addition, it can serve as a non-invasive biomarker for cancer.

3-Tyrosine, in contrast to the para isomer, is readily racemized. The majority of the load was metabolized to m-hydroxyphenylacetic acid but m-hydroxymandelic acid and 3,4-dihydroxyphenylacetic acid were also detected. Low circulating levels of m-tyrosine in the plasma suggest that most of the load is held due to a first pass effect somewhere in the enterohepatic system and that this portion of the load is not in equilibrium with the plasma m-tyrosine. The metabolism of a m-tyrosine may give further insight into the deficiencies of the phenylalanine hydroxylating system found in the various phenotypes of phenylketonuria. 3-Tyrosine has been used experimentally as a substitute for L-DOPA in the treatment of Parkinsonism. 3-tyrosine mimics the action of Dopa in two experimental animal models. It was also obvious from the experiments with d,l- and l-m-tyrosine that only the l-isomer (3-Tyrosine) is active.

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 The drug was withdrawn from the US market in March 2007 and from the Canadian market in August 2007.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.

Methixene is a tertiary antimuscarinic with actions similar to those of atropine; it also has antihistaminic and direct antispasmodic properties. It is used for the symptomatic treatment of parkinsonism, including the alleviation of the extrapyramidal syndrome induced by other drugs such as phenothiazines, but, like other antimuscarinics, it is of no value against tardive dyskinesias. Metixene has been discontinued. Parkinsonism is thought to result from an imbalance between the excitatory (cholinergic) and inhibitory (dopaminergic) systems in the corpus striatum. The mechanism of action of centrally active anticholinergic drugs such as metixene is considered to relate to competitive antagonism of acetylcholine at muscarinic receptors in the corpus striatum, which then restores the balance.

CYCRIMINE is an antispasmodic drug used for the treatment of Parkinson's disease (PD). It binds the muscarinic acetylcholine receptor M1, effectively reducing levels of acetylcholine. This decrease in acetylcholine restores the normal dopamine-acetylcholine balance and relieves the symptoms of PD.

Ethopropazine is an anticholinergic drug. Ethopropazine is an inhibitor of butyrylcholinesterase and non-selective muscarinic acetylcholine receptor antagonist. Ethopropazine has been used for the treatment of parkinsonism and drug-induced extrapyramidal reactions. Also It used for the symptomatic treatment of hepatolenticular degeneration and congenital athetosis.

Caramiphen is a muscarinic M1 acetylcholine receptor antagonist, which was used for the treatment of Parkinson Disease and cough, but then there using were discontinued. Caramiphen is also used in local anesthesia, and effect could be achieved through the suppression of voltage-gated Na⁺ currents.

Vanillin (4-hydroxy-3-methoxybenzaldehyde), a pleasant smelling organic aromatic compound, is widely used as a flavoring additive in food, beverage, cosmetic and drug industries. It is reported to cross the blood brain barrier and also displayed antioxidant and neuroprotective activities. Vanillin is a natural substance widely found in many plant species and often used in beverages, foods, cosmetics, and pharmaceutical products. Antioxidant and anticancer potential have been described for this compound. Vanillin has been classified as a bioantimutagen and is able to inhibit mutagenesis induced by chemical and physical mutagens in various cell systems. Vanillin, a selective agonist of TRPV1, has been shown to attenuate i.c.v. STZ and AlCl3+d-galactose induced experimental Alzheime's disease (AD).

Naringin is a flavanone plant metabolite which found in citrus fruits and in quantitatively significant amounts from grapefruit in particular. Naringin has attracted attention as a dietary supplement purported to aid in fat and weight loss. Ingestion of naringin and related flavonoids can interfere with the absorption and metabolism of certain drugs, and therefore consumption of grapefruit juice with medication is advised against. Naringin possesses numerous biological properties such as antioxidant, anti-inflammatory, and anti-apoptotic activity. It has been extensively studied in pre-clinical models of atherosclerosis, cardiovascular disorders, diabetes mellitus, neurodegenerative disorders, osteoporosis, and rheumatological disorders, and several different cancer models.

Smilagenin (also known as PYM50028 and Cogane) is a constituent of Jamaican sarsaparilla (Smilax ornata) and is a neuroprotectant that has been evaluated in Phase II clinical trials in Parkinson's disease and Alzheimer's disease. On 27 September 2011, the European Commission to Phytopharm plc, United Kingdom, granted orphan designation for smilagenin for the treatment of amyotrophic lateral sclerosis. The details of the mechanism of action of smilagenin are incomplete but involve the upregulation of neurotrophic factors including Glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor.