Protocatechuic acid (3,4-dihydroxybenzoic acid, PCA) is a simple phenolic acid. It is found in a large variety of edible plants and possesses various pharmacological activities. This bioactive compound is famous for its biological properties and pharmacological activities such as: antioxidant, antibacterial, anticancer, antiulcer, antidiabetic, antiaging, antifibrotic, antiviral, anti-inflammatory, analgesic, antiatherosclerotic, cardiac, hepatoprotective, neurological and nephroprotective. The neuroprotective effects of PCA, extracted from Alpinia oxyphylla, on H2O2 resulted in apoptosis and oxidative stress in cultured PC12 cells. Apoptotic cell death by H2O2 was dose-dependent. Enhanced effect of PCA on protecting PC12 cells against apoptosis, augmented glutathione (GSH) level and an increase in catalytic activity was investigated by flow cytometric analysis. In cytotoxic assays, PCA causes cell death in HepG2 cancerous cell line of liver showing that PCA stimulates the c-Jun N-terminal kinase (JNK) and p38 subgroups of the mitogen-activated protein kinase (MAPK) family. Treatment with PCA decreased OVA-induced airway hyper-responsiveness to inhaled methacholine. Cell inflammation and mucus hypersecretion was also decreased by PCA. Thus, PCA can be useful for treating asthma. Experimental studies strongly support the role of protocatechuic acid in the prevention of neurodegenerative processes, including Alzheimer's and Parkinson's diseases, due to its favorable influence on processes underlying cognitive and behavioral impairment, namely accumulation of the β-amyloid plaques in brain tissues, hyperphosphorylation of tau protein in neurons, excessive formation of reactive oxygen species and neuroinflammation.

The genus Rhodiola (Crassulaceae) consists of nearly 200 species and among them Rhodiola rosea L. is the best known. The plant is indigenous to the arctic regions of eastern Siberia, but it is also found in the northern parts of Europe and Alaska. Similar to Siberian ginseng, the root of R. rosea is traditionally used as a tonic in Russia, and as an antidepressant and anti inflammatory drug. Rosiridin, a monoterpene, has mainly stimulant properties and elicits the greatest monoamine inhibitory effect. Rosiridin is noted as specifically inhibiting MAO-B to a significant extent (over 80%), and shows potential beneficial effect in depression and senile dementia.

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.

Isatin (1H-indole-2,3-dione) is a naturally occurring heterocycle that was first synthesised by Erdmann and Laurent in 1840. Isatin possesses a wide range of biological activities. Isatin has anxiogenic, sedative, anticonvulsant activities and acts as a potent antagonist on atrial natriuretic peptide receptors in vitro. Isatin is an endogenous monoamine oxidase (MAO) inhibitor involved in stress and anxiety. Additionally, isatin inhibits alkaline phosphatase (ALP), nitric oxide (NO)-stimulated soluble guanylate cyclase, and other enzymes.

Norharman or beta-carboline (9H-pyrido[3,4-b]indole) is a neuroactive alkaloid first isolated from Peganum harmala L. It is implicated in a number of human diseases including Parkinson's disease, tremor, addiction and cancer. Norharman formed endogenously but external sources have been identified (among others fried meat and fish, meat extracts, alcoholic drinks, coffee brews, tobacco smoke). It inhibits monoamine oxidase and indoleamine 2,3-dioxygenase. In addition norharman binds with high affinity to imidazoline I2B receptors. Plasma norharman levels are elevated in chronic alcoholics and Parkinson's disease patients.