The antidepressant effects of Lavender
Systematic review and meta-analysis of RCTs trials by Firoozeei and colleagues from Tehran University of Medical Sciences in Iran
Firoozeei and colleagues from the Tehran University of Medical Sciences publish a systematic review and meta-analysis of randomized controlled clinical trials looking at the antidepressant effects of Lavender (Lavandula angustifolia) (Firoozeei et al., 2021).
Antidepressant drugs, such as selective serotonin reuptake inhibitors (SSRI) that aim at increasing serotonin levels in the brain, are accompanied with a high rate of adverse effects. Due to the limitations of antidepressant drugs, complementary and alternative medecine (CAM) disciplines can offer a valuable therapeutic approach.
While previous reviews report on the anxiolytic action of Lavender (Perry et al., 2012; Donelli et al., 2019), the present study aims at evaluating the antidepressant effects of Lavender in depressed patients or people affected by other diseases with concomitant depressive symptoms.
The keyword search spans 20 years (2000-2020), is conducted in a number of databases and includes terms such as depression, major depress* (wildcard) and antidepressant.
Firoozeei and colleagues leave no doubt about the genus and species they are looking to evaluate, i.e. Lavandula angustifolia. They explicitely exclude any other Lavender species and they include the botanical name in their keyword search.
The search yields 342 studies, of which 19 articles are included in the systematic review and 17 articles (1486 participants of which 754 cases and 732 controls) are included in the meta analysis.
These studies use different routes of administration:
- primarily aromatherapy (meaning here the olfactory/respiratory paths, using a soaked cotton ball, fabric, tissue or paper towel attached to the collar; rubbing lavender oil on the hands and breathing it in; the usage of an aroma diffuser; steam inhalation; breathing in the aroma from a glass container),
- oral (1 trial: Silexan® capsule; four other trials use dried Lavender flowers instead of the essential oil, in the form of herbal tea and capsules),
- dermal (cream) (2 trials with and without a foot bath in healthy pregnant or postpartum women),
- aromamassage (2 trials, one of which studied foot massage on female elderly patients with acute coronary syndrome, ACS; a second trial used a 30 min weekly back massage, during 4 weeks, with hospice cancer patients).
The most frequently used measurement instruments are the Beck Depression Inventory (BDI), the Depression, Anxiety and Stress Scale – 21 Items (DASS-21) and the Hospital Anxiety and Depression Scale (HADS).
The authors report significant efficacy of Lavender in decreasing depression scores.
The effect is marginally more pronounced in participants with diagnosed depression and is statistically significant in patients having other diseases with concomitant depressive symptoms.
The research team also performs a subgroup analysis: the oral route turns out to be the most effective route of administration. The authors praise the oral route as the most promising method of administration, citing Homayun et al. (2019): sustained and controllable delivery, ease of administration and patient compliance.
However, oral administration of essential oils is complex and not free of risk.
- As a general rule, yet depending on the botanical species and extraction method used, specific risks limit the oral application of essential oils. The main risks of administering essential oils to the gastrointestinal tract are irritation and inflamation of the mucuous membrane (Tisserand R., Young R., 2014, pp. 123–130).
- In addition, because of the risk of hepatotoxicity, guidelines for oral administration often reserve the use to adults, warn against the use during pregnancy or for women who are breastfeeding, and proscribe the use in case of impaired liver function*.
- Further, both the individual’s appreciation, as well as her/his acceptance or rejection of both the scent and the taste of an essential oil can complicate oral admininistration. While encapsulating the esssential oil (partly) deals with this issue and can prevent irritation of the gastrointestinal tract, hepatotoxicity still remains a concern.
Five trials, included in the meta analysis, use oral administration. One trial uses Silexan capsules (Kasper et al., 2016); four trials use dried Lavender flowers instead of the essential oil, in the form of herbal tea and capsules. Silexan is a proprietary essential oil from Lavandula angustifolia flowers complying with the monograph Lavender oil of the Ph. Eur. and exceeding the quality definitions of the Ph. Eur. (Müller et al., 2021). Silexan has been extensively researched over the past 10 years, evaluating its anxiolytic and anti-depressant properties (Müller et al., 2021).
* As an example, read the notice of Laseaxan, a Silexan-based product available through pharmacies in Belgium.
Let’s have a closer look at the reported adverse effects. Three trials using oral administration report side effects; one study used inhalation.
As far as the inhalation study is concerned, two patients out of 37 (all received both Lavender and placebo in a cross-over design) complained of headache; three of them suffered from cough. The observed adverse events were resolved after discontinuing the intervention (Lari et al., 2020).
The side effects, reported by the trials using oral administration, include: nausea, eructation (the release of air or gas from the stomach or esophagus through the mouth), drowsiness, headache, palpitation, diarrhea and nasopharyngitis (an inflammatory attack of the pharynx and nasal cavities). The trial using Silexan through oral administration reports eructation as a marked difference between the treatment groups (Kasper et al., 2016).
Picking a route
The question is: do we need the oral route? In other words, is the intake of Lavender (essential oils is what my article is primarily about) necessary to obtain the desired action on depression? Or does the olfactory route (inhalation, diffusion, aromamassage – yes, topical application is about an olfactory experience) and its pharmacological and psychological mechanisms of action do the job, requiring less precautions than oral administration?
Inhalation and dermal application is known to be less risky than oral administration. Often, the risk of an adverse reaction can be coped with by simple measures, such as dilluting in a carrier oil (dermal application), limiting the exposure time (diffusion) or the frequency of application (inhalation).
Nearly half of the studies used the inhalation route. Here, the effects of Lavander may be attributed to the olfactory pathway. The authors describe a number of advantages of the olfactory path citing Lv et al. (2013): bypassing the blood brain barrier, permitting a speedy onset of action (without the interference of the blood brain barrier), resulting in much fewer adverse effects.
The authors describe a number of advantages of the olfactory path citing Lv et al. (2013): bypassing the blood brain barrier, permitting a speedy onset of action (without the interference of the blood brain barrier), resulting in much fewer adverse effects.
Let’s take a sidestep and look at what research is telling us about the routes of administration in the case of anxiety. In their 2019 systematic review and meta analysis, an Italian team studies the efficacy of Lavender, in any form of administration, on anxiety and anxiety-related conditions (Donelli et al., 2019).
65 Randomized Controlled Trials (7993 participants) and 25 Non-Randomized Studies (1200 participants) are included in the qualitative synthesis, 37 RCTs (3964 participants) make it to the quantitative synthesis (meta analysis). The meta analysis showed that Lavender inhalation can significantly reduce anxiety levels, as well as state anxiety and trait anxiety. Similar to Firoozeei’s 2021 study on depression, oral administration of Silexan and the application of massage with Lavender essential oil also show a significant effect in reduced anxiety levels.
When it comes to adverse effects, Donelli and colleagues found a limited number of the included studies report adverse effects. The main adverse effects were reported in seven studies: headaches, palpitations, infections and gastrointestinal disorders: eructation, diarrhea, breath odor and dyspepsia (indigestion). Six of these seven studies use oral administration of Silexan; one trial uses capsules containing 500 mg of Bitter orange or Lavender flower powder.
It seems fair to state that diffusion, inhalation and massage therapy with Lavender essential oil offer safe modalities that allow us to benefit from one of nature’s finest scents – if and only if the receiver welcomes the scent. I have been polling during my teachings, for the past five years, who in the classroom did not appreciate the scent of Lavender. It shows a quite consistent 10% of participants who demonstrate an aversion for the scent of Lavender. While this is not science (!), it does say something about the primary risk we must deal with in our practice, that is odour preference. Scent is, it cannot be stressed enough, above all an individual experience.
It seems fair to state that diffusion, inhalation and massage therapy with Lavender essential oil offer safe modalities that allow us to benefit from one of nature’s finest scents – if and only if the receiver welcomes the scent.
For topical applications, Lavender essential oil is in the low-risk zone. True lavender (Lavandula angustifolia subsp. angustifolia), as well as Spike lavender (Lavandula latifolia Medik., L. Spica) are commonly used for their beneficial action on several skin conditions. In addition, proper dillition into a carrier oil is likely to prevent irritation (irritant contact dermatitis).
EU’s 1223/2009 cosmetics regulation imposes the labeling of specific allergens on products containing Lavender essential oil when taken to market as cosmetics (not as food supplements). The regulation allerts for the possible risks of allergic reactions (allergic contact dermatitis or delayed hypersensitivity and contact urticaria or immediate hypersensitivity) by imposing product labeling for a series of substances, in relation to their concentrations in the final product. As an example for Lavender essential oil, cosmetics will get labeled with linalool if the concentration is higher than 0,001% in leave-on products. Dillution in a carrier oil might not rule out a potential allergic reaction.
If you’re interested in the more than 10 year old debate about a potential action of Lavender on the endocrine system, read Petra Ratajc’s prodigious article on potential hormone disrupting effects of Lavender.
Finally, if you believe (like I do) it’s a bad idea to propose a full body massage with a single Lavender essential oil (diluted in a carrier oil), because that would be (read: smell) simply too much, it is good practice to blend Lavender with floral, citrus or even certain woody essential oils. The Aromatic Plant Extract Index at aroma.news is designed to help you explore aromatic plant extracts, based on aromatic families and base, heart and top notes.
Photo Annie Spratt @ unsplash.com
Silexan is a trademark of Dr. Willmar Schwabe Gmbh & Co.