Clinical and Neurobiological Effects of Aromatherapy on Depression and Sleep Disorders: A Systematic Review

Abstract

Aims: This systematic review evaluated the clinical efficacy of aromatherapy and the neurobiological mechanisms underlying its effects on depressive symptoms and sleep quality in adults with depression-sleep comorbidity. Study Design: A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines. Place and Duration of Study: The literature search was performed in PubMed/MEDLINE, Scopus, Web of Science, and the Cochrane Library, and included studies published from January 2018 to January 2025. Methodology: Search terms related to aromatherapy, essential oils, depression, sleep disorders, insomnia, and neurobiological mechanisms were combined and adapted for each database. Eligible studies included randomised controlled trials, quasi-experimental studies, observational research, and relevant preclinical studies evaluating inhaled or topically applied essential oils. Outcomes included depressive symptoms, sleep quality, and neurobiological markers associated with stress and emotional regulation. A total of 103 records were initially identified. After duplicate removal and title, abstract, and full-text screening according to predefined eligibility criteria, 18 studies were included in the qualitative synthesis. Results: Aromatherapy was associated with modest but consistent improvements in depressive symptoms and sleep quality, particularly among individuals with mild to moderate depression and non-organic sleep complaints. Lavandula angustifolia and Citrus bergamia were the most frequently studied essential oils. Reported outcomes included reduced depressive symptom scores, shorter sleep-onset latency, fewer nocturnal awakenings, and improved subjective sleep quality. Neurobiological findings suggested modulation of limbic activity, regulation of the hypothalamic-pituitary-adrenal axis, reductions in salivary cortisol, and interactions with gamma-aminobutyric acid and serotonergic systems. Conclusion: Aromatherapy may be considered a complementary intervention for depression-sleep comorbidity, although stronger trials are required to confirm its effectiveness and mechanisms.