Neuropharmacological mechanisms and psychotherapeutic effects of essential oils: A systematic review

Abstract

Anxiety is characterized by excessive worry, fear, or uneasiness which can interfere with daily activities and relationships. Neurotransmitters like gamma-aminobutyric acid (GABA), serotonin, and dopamine affect mood, neurological functions, behaviour, cognition, and overall mental health. Imbalances in these neurotransmitters are linked to mental health disorders like depression and anxiety. In recent years, there has been an increase in the use of essential oils (EOs) in the management of the symptoms associated with anxiety and depression due to their perceived therapeutic advantages. This systematic review aimed to examine the psychotherapeutic effects and neuropharmacological mechanisms of EOs and their chemical constituents in animal studies related to various mental health conditions. A search of the literature was undertaken using the online databases PubMed, Embase, Scopus, and Web of Science, focusing on articles published until December 2023. The keywords used included "psychotherapeutic," "animal model," "neuropharmacology," "essential oil," "plant species," "anxiety," and "depression". Manual searches were also conducted online and in Google Scholar. A total of 31 research studies that met the objectives of the study were found. The results of the studies showed that EOs demonstrated significant psychotherapeutic benefits, such as anxiolytic and antidepressant effects, in animal models, mediated by modulating neurotransmitters and signalling pathways linked to mood, emotion, and anxiety regulation. Studies examined the effects of EOs extracted from plants, including Lavandula angustifolia Moench (Lamiaceae), Citrus aurantium L. (Rutaceae), Curcuma caesia Roxb. (Zingiberaceae); Melissa officinalis L. (Lamiaceae); Piper nigrum L. (Piperaceae), Citrus reticulata Blanco. (Rutaceae); Curcuma caesia Roxb. (Zingiberaceae); Cymbopogon citratus (DC.) Stapf (Poaceae), Cinnamomum cassia Presl. (Lauraceae), Melissa officinalis L. (Lamiaceae); Eugenia caryophyllata Thunb. (Myrtaceae) and Citrus bergamia L. (Rutaceae), which are considered as food flavouring plants. EOs predominantly modulate pro-inflammatory cytokines such as interleukin (IL)-6, IL-1β, tumor necrosis factor alpha (TNF-α), and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signalling pathways to regulate anxiety and depressive symptoms. They possess anti-inflammatory and antioxidant properties, reducing the inflammation and oxidative stress associated with anxiety and depression, while also increasing GABA signalling gene expression. This systematic review found that animal studies provide evidence for the psychotherapeutic effects of EOs, suggesting their potential as a safer alternative to conventional medications for anxiety and depression. However, further research is needed to validate these findings and determine optimal dosage and administration methods.