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Systematic Review and Meta-analyses of Lavender for Anxiety
ISSUE:
Page:
33-34

Reviewed: Donelli D, Antonelli M, Bellinazzi C, Gensini GF, Firenzuoli F. Effects of lavender on anxiety: A systematic review and meta-analysis. Phytomedicine. 2019;65:153099. doi: 10.1016/j.phymed.2019.153099.

Worldwide, up to 15% of the general population is affected by anxiety disorders. Lavender (Lavandula spp., Lamiaceae) flower essential oil is a traditional remedy for anxiety and has demonstrated anxiolytic and sedative properties. The purpose of this systematic review and meta-analyses was to evaluate the effects of lavender on anxiety and anxiety-related disorders.

The study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed, Scopus, Web of Science, Cochrane Library, Embase, and Google Scholar were searched from inception up to November 2018 using the terms “lavender,” “lavandula,” “Silexan,” “anxiety,” “anxious,” and “anxiolytic.”

Systematic Review

Included in the systematic review were randomized controlled trials (RCTs) and non-randomized studies (NRSs) that evaluated lavender (any species, any preparation form, any route of administration) for anxiety using any type of comparator and a validated instrument to assess anxiety. The authors excluded animal and in vitro studies and trials with unclear/unspecified sample sizes or missing data. Also excluded were studies that used lavender blends of unknown composition, with unspecified proportions, or in which lavender did not account for the majority of the blend.

A total of 90 articles met the systematic review criteria, including 65 RCTs (N = 7,993) and 25 NRSs (N = 1,200). The RCTs had a range of 13 to 597 participants with a mean sample size of 90. A single, acute dose of lavender was evaluated in 38 RCTs, and chronic lavender treatment was evaluated in 27 RCTs. The most commonly evaluated lavender species was L. angustifolia, and the most common route of administration was inhalation/aromatherapy (49 RCTs), followed by topical (10 RCTs) and oral (6 RCTs). Controls included placebo, usual care, no intervention, and positive control. The most commonly used outcome measures were the State-Trait Anxiety Inventory (STAI), Zung Self-Rating Anxiety Scale (Zung SAS), and Hamilton Anxiety Rating Scale (HAM-A).

Of the 65 RCTs included in the systematic review, 54 RCTs (83%) found that lavender significantly improved anxiety compared with baseline or control (P < 0.05), and 11 RCTs concluded that lavender had no significant benefit. Of the 25 NRSs, 17 (68%) reported that lavender had a significant beneficial effect on anxiety. Seven studies (six RCTs and one NRS) reported adverse events (AEs), which included headaches, palpitations, infections, and gastrointestinal disorders. No serious AEs were reported. Risk of bias (RoB) was assessed with the Cochrane Collaboration RoB tool. Considering performance bias as a key domain, the overall quality of the evidence was rated as low, with approximately 89% of the RCTs characterized by a high RoB. When performance bias was not considered a key domain (e.g., topical application and inhalation studies in which blinding is difficult), 71% of the RCTs had a high overall RoB.

Meta-analyses

In addition to the systematic review, the authors conducted several separate meta-analyses. Included RCTs evaluated patients with anxiety, in an anxiety-inducing setting, or performing an anxiety-inducing activity, and used validated scales to quantify anxiety levels. Interventions were oral administration of the proprietary, standardized lavender essential oil (LEO) product Silexan® (Dr. Willmar Schwabe GmbH & Co. KG; Karlsruhe, Germany), LEO inhalation, or massage with LEO; and comparators were usual care, no intervention, sham intervention, placebo, or massage without LEO.

A total of 37 of the 65 RCTs met these criteria and were included in seven separate meta-analyses.

  1. Meta-analysis of five RCTs (N = 1,173) evaluating the effect of 80 mg/day of Silexan on anxiety measured with the HAM-A indicated that Silexan significantly reduced anxiety compared to placebo (P = 0.004).
  2. Meta-analysis of three RCTs (N = 451) assessing the effect of 80 mg/day of Silexan on anxiety measured with the Zung SAS indicated that Silexan significantly reduced anxiety compared to placebo (P = 0.02).
  3. Meta-analysis of 12 RCTs (N = 901) evaluating the effect of LEO inhalation on state anxiety measured with the STAI-State indicated LEO significantly reduced anxiety compared to the controls (P = 0.0006). Subgroup analyses of situations inducing high-anxiety and mild-anxiety revealed that in both cases LEO significantly reduced anxiety compared to the controls (P = 0.04 and P = 0.06, respectively).
  4. Meta-analysis of four RCTs (N = 196) assessing the effect of LEO inhalation on trait anxiety measured with the STAI-Trait indicated that LEO significantly reduced anxiety compared to the controls (P = 0.01).
  5. Meta-analysis of six RCTs (N = 398) evaluating the effect of LEO inhalation on systolic blood pressure (a proxy for anxiety levels) compared to no intervention or to sham intervention indicated that LEO had no significant effect.
  6. Meta-analysis of 24 RCTs (N = 1,682) assessing the effect of LEO inhalation on anxiety measured with any validated scale indicated that LEO significantly reduced anxiety compared to the controls (P < 0.0001). Subgroup analyses showed that LEO significantly reduced anxiety compared to the controls in high-anxiety situations (P < 0.0001) but not in mild-anxiety situations.
  7. Meta-analysis of six RCTs (N = 448) evaluating the effect of LEO massage on anxiety measured with any validated scale compared to other physical therapies or usual care indicated that LEO significantly reduced anxiety compared to the controls (P < 0.001), and this effect was maintained in the subgroup analysis of high-anxiety situations.

Conclusion

In summary, the meta-analyses indicate that oral Silexan and LEO inhalation can significantly reduce anxiety compared to controls. Massage with LEO also appears to reduce anxiety, but more research is needed to demonstrate that the benefit is due to a specific effect of lavender.

The limited safety data indicate that lavender is well-tolerated with no serious AEs. Acknowledged limitations include the low quality of evidence and high RoB of the included RCTs and the heterogeneity of the study designs.

“Further high quality RCTs with more homogeneous study designs are needed to confirm these findings,” the authors wrote. “[S]ince 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.”