Editor's Note

Stress is an integral part of human life and is a commonly reported ailment in modern life. Exposure to high levels of stress can disrupt daily function and have a negative effect on performance and behavior, as well as lead to chronic illness. The negative effects of stress on health and cognition can be improved with a variety of approaches, including the use of traditional herbs. Lavender (Lavandula spp.) from the mint family (Lamiaceae) family is recognized as one of the important medicinal plants for stress management. In recent years, many preliminary studies have been conducted on the effect of lavender on the stress, however, these studies examined the effect of lavender in small sample sizes. Authors here conduct a systematic review and meta-analysis study to estimate the pooled effect of lavender on stress. 21 articles published prior to August 2021 that assessed the effect of lavender on stress were included, for a total of 791 subjects in the intervention groups & 804 in the control groups. The analysis shows a statistically significant pooled decrease in stress score was observed as 0.63 ± 0.13 (95% CI) for the patients using lavender as compared to control groups  (P < 0.001). The authors propose that the use of lavender should be considered as a part of stress management programs.
Abstract

Background
Lavender is considered as one of the medicinal plants to manage stress. Although many preliminary studies evaluated the effect of lavender on individuals’ stress level, to the best of our knowledge, we did not find a study that summarizes the results. Therefore, the present study aimed to estimate the Pooled effect of lavender on the stress level of individuals using systematic review and meta-analysis.

Method
A systematic literature review based on PRISMA 2020 was performed on the SID, MagIran, Embase, PubMed, Scopus, Web of Science (WoS) databases, and Google Scholar motor engine using related MeSH/Emtree and ‎Free Text words,‎ including “Lavender*”, “Lavandula*”, “Stress*”, “Stress Disorders, Traumatic”, and “Stress, Psychological” with no time limitation until August 2021: We also searched two Iranain free local resourses including MagIran https://www.magiran.com and Scientific Information Database (SID) https://www.sid.ir. The quality assessment of studies was performed using JBI checklist. Heterogeneity among studies was quantified using I2 index and Random Effects model was used to combine the data and perform the meta-analysis.

Results
In the initial search, 1520 articles were found. After excluding the irrelevant studies, finally, 21 articles with a sample size of 791 in the intervention group and 804 in the control group were included in the meta-analysis. As a result of combining the studies, stress score after using lavender in the intervention group showed a significant decrease of 0.63 ± 0.13 (95% CI) more than that in the control group (P < 0.001). The results of subgroup analysis demonstrated that the highest standardized mean difference (SMD) before and after the intervention in the intervention group compared to the control group was related to L. angustifolia species with 0.73 ± 0.22, student groups with 2.27 ± 1.34, and diagnostic tool of Perceived Stress Scale (PSS) with 0.82 ± 0.42, indicating that the difference between the groups was statistically significant (P < 0.001).

Conclusion
The pooled estimation of this systematic review and meta-analysis revealed that lavender significantly reduces individuals’ stress. Therefore, it seems that the use of lavender can be considered as a part of a stress management programs, especially in student groups.
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