Plants and phytochemicals potentials in tackling anxiety: A systematic review

Abstract

Background: Anxiety is one of the psychiatric disorders that disturbs routine life including moods and motivation. Excessive anxiety causes mental illnesses or anxiety disorders, which are commonly treated by synthetic medicines. Recently, there is a substantial increase in the studies of phytochemicals as alternatives to first-line conventional anxiolytic drugs. Yet there is insufficient information about the mechanisms of how these bioactive constitutes from plants manage anxiety disorders. This systematic review aims to answer the following research questions: (1) Which plant extracts and phytochemicals have anxiolytic effect? what is the mechanism of action? (2) Have human trials been conducted to confirm their anxiolytic effect? (3) If not, which plants/phytochemicals are recommended for further human trials? Methodology: To define and summarize such information, this systematic review consolidated in vitro, preclinical, and clinical studies that examine the anti-anxiety activity of plant extracts via oral administration, conducted through three scientific databases including PubMed, Scopus, and Google Scholar following the PRISMA protocol. Results and conclusion: Similar to synthetic drugs, most bioactive phytochemical compounds modulate anxiolytic activity through six main neurotransmitter pathways including acetylcholine (ACh), γ-aminobutyric acid (GABA), glutamate, serotonin (5-HT), dopamine (DA), and norepinephrine (NE). These bioactive compounds mainly belong to phenolics, alkaloids, and terpenoids, and they demonstrated effective therapeutic benefits against anxiety symptoms. Four plants, including Aloysia polystachya, Lavandula angustifolia, Matricaria chamomilla L. and Humulus lupulus, have been evaluated in human trials. However, studies on majority plants were performed using animal models, and among them, Tanacetum parthenium L. Schultz-Bip (Asreraceae), demethoxysudachitin, Albizzia julibrissin, Nelumbo nucifera Gaertn. leaves, Zizyphi spinosi semen seed extract, obovatol, Mangifera indica stem barks, Nectandra grandiflora Ness and Lavandula angustifolia, Bupleurum yinchowense roots, Citrus aurantium L. and Foeniculum vulgare exhibited the most significant anxiolytic effect at dosage of 30 mg/kg/day or lower. Further human trials are recommended to validate the efficacy and safety of these plants/plant extracts/phytochemicals in managing psychiatric disorders.

Keywords

• Anxiety
• Anxiolytic
• Plants
• Phytochemicals
• Mechanisms