Background and aims: Antidepressant drugs are accompanied with high rate of adverse effects. Lavender is one of the most common herbal drugs mentioned in Traditional Persian literature with potential efficacy on mental disorders and less serious side effects. Thus, the aim of this study was to determine the efficacy of lavender on depression severity by preforming a systematic review and meta-analysis.

Methods: Databases including PubMed, Scopus, Cochrane library, Embase and Web of science were searched for relevant articles till December 2020. Quality of studies were evaluated by Jadad scale and the Cochrane collaboration tool. Depression as endpoint measure or as a subscale of any valid assessment tool was subjected to quantitative data analyses. Both fixed and random effects meta-analysis were conducted for data synthesis.

Results: Out of 342 screened studies, 17 articles were included in the meta-analysis. Results showed significant efficacy of lavender in decreasing depression scores compared to the control group (pooled Standardized Mean Difference (SMD)= -0.66, 95 % CI: -0.85 to -0.46;P < 0.001, I² = 68.2 %;). Subgroup analysis proved that the effect of lavender was marginally more pronounced in participants with diagnosed depression (pooled SMD= -0.62, 95 % CI: -1.26 to 0.01, P = 0.055; I² = 88.1 %) while its effect was statistically significant in patients having other diseases with concomitant depressive symptoms (pooled SMD= -0.65, 95 % CI: -1.84 to -0.46, P < 0.001; I² = 52.1 %), and the oral route (pooled SMD= -0.56, 95 % CI: -1.07 to -0.05, P = 0.032; I² = 85.2 %;) was the most effective route of administration.

Conclusions: This systematic review and meta-analysis concluded that lavender has significant antidepressant effects. However, due to some limitations, further large clinical trials are recommended with more homogeneous populations and rigorous designs.