Research Paper on Lavender for Anxiety: Systematic Review & Meta-Analysis

Background

Anxiety is one of the uprising psychiatric disorders of the last decades and lavender administration has been traditionally suggested as a possible treatment. The objective of this review is to assess the efficacy of lavender, in any form and way of administration, on anxiety and anxiety-related conditions.

Methods

The PRISMA guidelines were followed. Retrieved data were qualitatively and quantitatively synthesized. Randomized Controlled Trials (RCTs) and Non-Randomized Studies (NRSs) which investigated the efficacy of lavender, in any form and way of administration, on patients with anxiety, involved in anxiety-inducing settings or undergoing anxiety-inducing activities, compared to any type of control, without language restrictions, were identified through electronic database searches. Medline via PubMed, Scopus, Web of Science, Cochrane Library, EMBASE, and Google Scholar were systematically searched. All databases were screened up to November 2018. Risk of bias was assessed with the Cochrane risk-of-bias tool and the following domains were considered: randomization, allocation sequence concealment, blinding, incomplete outcome data, selective outcome reporting, and other biases.

Results

65 RCTs (7993 participants) and 25 NRSs (1200 participants) were included in the qualitative synthesis and 37 RCTs (3964 participants) were included in the quantitative synthesis. Overall, the qualitative synthesis indicated that 54 RCTs and 17 NRSs reported at least a significant result in favor of lavender use for anxiety. The quantitative synthesis showed that lavender inhalation can significantly reduce anxiety levels measured with any validated scale (Hedges’ g = −0.73 [95% CI −1.00 to −0.46], p < 0.00001, 1682 participants), as well as state anxiety (Spielberger's state-trait anxiety inventory (STAI)-State mean difference = −5.99 [95% CI −9.39 to −2.59], p < 0.001, 901 participants) and trait anxiety (STAI-Trait mean difference = −8.14 [95% CI −14.44 to −1.84], p < 0.05, 196 participants). Lavender inhalation did not show a significant effect in reducing systolic blood pressure as a physiological parameter of anxiety. A significant effect in diminishing anxiety levels was also found in favor of the use of oral Silexan® 80 mg/die for at least 6 weeks (Hamilton Anxiety Scale mean difference = −2.90 [95% CI −4.86 to −0.95], p = 0.004, 1173 participants; Zung Self-rating Anxiety Scale mean difference = −2.62 [95% CI −4.84 to −0.39], p < 0.05, 451 participants) or of the administration of massage with lavender oil (Hedges’ g = −0.66 [95% CI −0.97 to −0.35], p < 0.0001, 448 participants).

Discussion

The most important limitation of this review is the low average quality of available studies on the topic. The majority of included RCTs were characterized by a high overall risk of bias. Another limitation regards the heterogeneity of study designs, especially with regard to non-oral ways of administration. Overall, oral administration of lavender essential oil proves to be effective in the treatment of anxiety, whereas for inhalation there is only an indication of an effect of reasonable size, due to the heterogeneity of available studies. Lavender essential oil administered through massage appears effective, but available studies are not sufficient to determine whether the benefit is due to a specific effect of lavender. Further high-quality RCTs with more homogeneous study designs are needed to confirm these findings. Available information outlines a safe profile for lavender-based interventions, although more attention should be paid to the collection and reporting of safety data in future studies. Considering these findings, since treatments with lavender essential oil generally seem safe, and, in the case of inhalation, also simple and inexpensive, they are a therapeutic option which may be considered in some clinical contexts.

Introduction

Need for the Study

The researchers identify the need for the study clearly. As they indicated, anxiety is one of the psychiatric disorders that has been on the rise. They wanted to test whether the administration of lavender essential oil is a treatment for anxiety. Using various works of literature, researchers discussed the prevalence of anxiety and related disorders and the way lavender essential oil has been useful for years as a treatment for the condition.

Research Hypothesis

The researchers hypothesized that patients in the intervention group would receive a placebo effect after inhalation of lavender essential oil, while those in the control group will have a nocebo effect.

Variables of Interest

Independent variables: Lavender essential oil

Dependent variables: Anxiety

Ways the Variables are Operationally Defined

The researchers asserted that the administration of lavender oil (the independent variable) controls anxiety (dependent variable) by relieving mild symptoms of mental stress and exhaustion, eventually enhancing sleep.

Method

Sample Size(Total): 13157. Size Per Group/Cell: 65 Randomized Controlled Trials (7993 participants) and 25 Non-randomized samples (1200 participants) were included in the qualitative analysis. Additionally, researchers included 37 RCTs (3964 participants) in the quantitative analysis.

Researchers described methods and procedures to ease replication without any further information. If I would want to find the effects of lavender oil on anxiety in another population or setting, I would incorporate the RCT method and procedures to get the study results that would without a doubt, be similar to the findings in the article discussed. I would replicate the use of the control and intervention groups to compare the results of the populations. Using such information in another study, there would be greater validity to the study findings.

Participants

Selection and Recruitment

In their synthesis review, researchers selected ninety qualitative and 37 quantitative articles that discussed the effects of lavender essential oils on anxiety. The study participants in the articles were adults over 18 years and had baseline anxiety levels.

Random Selection

The subjects in the articles were randomly selected and the research analyzed through randomized and non-randomized control trials.

Bias in Sampling

There was a high risk of bias in the RCT. According to the authors, the type of bias in RCT was the inhalation of lavender essential oil among participants because that type of administration makes it easy for participants to identify its smell.

Were the Samples Appropriate

The samples were appropriate and allowed for the generalizability of results. The articles for review used by the researchers had participants who were selected from high anxiety-inducing situations and mild anxiety-inducing situations.

Characteristics of Sample Population

The characteristics of the population included those undergoing colorectal surgery, curettage, and hemodialysis as well as patients who had primary dysmenorrhea and acute coronary syndrome. Also, the articles included samples of patients in the intensive care unit.

Research Design

Two groups classic experimental versus control group, randomly assigned

Discussion

Overall, the administration of lavender oil through inhalation has been confirmed to be effective in the reduction of anxiety levels. Administration through massage is also effective but the available studies are not enough to determine with certainty whether the benefits are due to a specific effect of lavender. The study is useful since people with anxiety can use lavender essential oil as a treatment for their condition.

Strength and Limitations of the Study

One strength of the article is the generalizability of research findings. Also, the meta-analysis increased statistical power because of the increase in sample size. On the contrary, the limitations of the article include low average quality of studies on the topic, a high risk of bias on the RCTs, and the possible misinterpretation of results due to the STAI instrument, which had two questionnaires.

Lesson Learned from the Study

It is recommended that further high-quality trials should be conducted by trying to make study designs more homogeneous and pay attention to safe data collecting and reporting.

Remaining Questions

Does diluting lavender in water reduce its effect?

Reference

Donelli D., Antonelli M., Bellinazzi C., Gensini F. G., & Firenzuoli F. (2019). Effects of lavender on anxiety: A systematic review and meta-analysis. Phytomedicine, 65. https://doi.org/10.1016/j.phymed.2019.153099