How Strong is the Evidence for the Anxiolytic Efficacy of Lavender?: Systematic Review and Meta-analysis of Randomized Controlled Trials

Purpose: Although lavender is purported to possess anxiolytic and sedative properties and is often recommended for relieving anxiety, the efficacy of lavender has not been well established. Thus, this review aimed to evaluate the anxiolytic effects of lavender aromatherapy. Methods: Ten data bases were searched for studies published between 2000 and 2018. Randomized controlled trials investigating the anxiolytic effects of lavender aromatherapy with any type of application for persons with or without clinical anxiety were included. The outcome variables included self-rated anxiety, vital signs, and salivary cortisol and chromogranin A (CgA) levels. In the meta-analysis, standardized mean difference and 95% confidence interval were calculated as effect measures by applying the random effect model and inverse variance method. Results: Twenty-two trials met our inclusion criteria. Lavender aromatherapy was found to have favorable effects in relieving anxiety (Hedges' (g) over cap = -0.65; 95% CI, -0.84 to -0.46) and decreasing systolic blood pressure ((g) over cap = -0.22; 95% CI, -0.43 to -0.02), heart rate ((g) over cap = -0.53; 95% CI, -0.74 to -0.32), and salivary cortisol ((g) over cap = -1.29; 95% CI, -2.23 to -0.35) and CgA ((g) over cap = -2.29; 95% CI, -3.24 to -1.34) levels. However, the meta-analysis did not reveal any significant effects of lavender on diastolic blood pressure (effect size: -0.17; 95% CI, -0.37-0.04). Conclusion: Aromatherapy using lavender oil might have favorable effects on anxiety and its physiological manifestations. Future studies are recommended with an emphasis on methodological quality. In nursing practice, it is suggested that lavender aromatherapy be included in programs intended to manage anxiety in patients across diverse healthcare settings. (C) 2019 Korean Society of Nursing Science. Published by Elsevier BV.