Can lavender take the edge off anxiety?

Everyone has experienced some level of anxiety. It’s the feeling of uncertainty and worry that isn’t always logical, but keeps you physically on edge in anticipation of some sort of threat. While evolutionarily^[1] it may have been beneficial to trigger a stress response and prepare the body for fighting or fleeing, as humans have progressed and slowly increased our consumption of information, stimulation, and exposure to bad news, the chances of firing up this useful feeling for relatively less logical or worrisome threats appear to have increased. Today, anxiety disorders are estimated to keep up to 15% of the general population^[2] on edge when threats are actually few and far between.

Anxiety disorders are characterized by an acute autonomic system activation accompanied by anticipation of a future threat and range from generalized anxiety disorder and phobias to panic attacks, as shown in Figure 1. They are twice as common^[3] in women, in comparison to men. Treatment can be drug-free through lifestyle changes and cognitive behavioral therapy, while anxiolytic drugs like selective serotonin reuptake inhibitors (SSRIs) or benzodiazepines can be effective but include some adverse effects, including delayed onset, dependence, tolerance, sedation, and cognitive impairment.

Lavender is an herbal remedy traditionally associated with anxiolytic properties and few adverse effects. The key active constituents^[4] of lavender that are responsible for its supposed calming and sedative effects are linanyl acetate and linalool. The herb is often administered in the form of essential oil distilled from the flower, and the oil can be used orally, topically, or through inhalation.

Various animal studies have been conducted to elucidate the underlying mechanism of action for the sedative effects of lavender. Mouse motility has been notably reduced following 60 minutes of lavender essential oil, linalool, and linalyl acetate inhalation in two separate studies^[5][6] from the same group. The anxiolytic properties^[7] of lavender seemingly come from the antagonization of NMDA and GABA-related receptors in the central nervous system that influence muscle contraction, as well as inhibition of the serotonin transporter.

The authors of the study under review conducted a systematic review and meta-analysis to determine the influence of lavender on anxiety and anxiety-related measures. They also evaluated the literature for the best method of lavender administration.

Lavender has traditionally been used as an anxiolytic. Animal studies have begun to uncover a potential mechanism for its effects, but clear evidence to support clinical use is lacking. The authors of the study under review designed a systematic review and meta-analysis with the aim of determining lavender’s efficacy and the best method of administration.

This systematic review and seven part random effects meta-analysis qualitatively and quantitatively analyzed randomized controlled trials (RCTs) and non-randomized studies (NRSs) that evaluated the effect of different methods of lavender administration (oral, topical, or inhaled) on anxiety.

Using the PICOS^[8] criteria (an attempt to simplify the identification of key study information, which stands for: Population, Intervention, Control/Comparison, Outcome, Study type), two investigators independently screened 685 articles and identified 65 RCTs and 25 NRSs for qualitative analysis and 37 RCTs for quantitative analysis, with a median number of participants of 90. In general, study participants were adults and/or elderly people. Their situations ranged from patients undergoing radiotherapy or open-heart surgery to healthy students, which represented people who would suffer from high anxiety to mild anxiety. The anxiety measured in these studies was mostly associated with these study situations or current life events. Very few studies looked at clinical anxiety disorders, such as generalized anxiety disorder. While inhalation was the most frequent method of lavender administration at a single dose, and water or usual care were the most common control, dilutions (about one to seven drops of of 0.5% to 10% lavender oil), durations of exposure (one to 45 minutes, one to three times per day, for one to 60 days), and comparisons varied widely (from distilled water to diluted milk or sesame oil).

The primary outcome was the change in participants’ symptoms of anxiety from lavender exposure in comparison to a placebo or other control (e.g. tea tree oil). Studies were included only when anxiety or related outcomes were assessed with a validated anxiety scale or when physiological measures related to an anxious state (e.g. heart rate, blood pressure) were recorded. Studies were excluded when lavender treatment blends were unclear in composition or dosage and when lavender was not the dominant ingredient. Risk of bias for RCTs was assessed with the Cochrane risk-of-bias tool. The study was preregistered with PROSPERO and followed PRISMA guidelines.

While qualitative analysis was relatively straightforward—researchers determined which studies demonstrated a significant improvement from baseline within the intervention group or in comparison to the control—quantitative analysis consisted of seven meta-analyses, depicted in Figure 2. The 37 RCTs were divided into three groups, depending on the method of lavender administration: 1) 80 milligrams of Silexan, a capsule preparation standardized to 35% of linalool and linalyl acetate (proposed active ingredients in lavender); 2) inhalation of lavender essential oil on a neutral support (cotton or handkerchief); and 3) massage with lavender essential oil. The RCTs were further divided depending on the scale or method of anxiety assessment. Subgroup analyses were performed to focus on high quality studies and meta-regression analyses were conducted when heterogeneity was high to identify moderators of the effect.

This systematic review and random effects meta-analysis qualitatively and quantitatively analyzed randomized controlled trials (RCTs) and non-randomized studies (NRSs) that evaluated the effect of lavender (oral, topical, or inhaled) on anxiety. Study participants were predominantly adults and elderly people, but exhibited a wide range of methods of lavender administration, dose, and duration of treatment. Study situations ranged from relatively high anxiety-inducing situations (e.g., patients in an intensive care unit) to more mild situations (e.g., students taking a test). The primary outcome was the change in the participants’ symptoms of anxiety from lavender exposure in comparison to a placebo or other control (e.g. tea tree oil). Seven meta-analyses were conducted on the 37 RCTs, depending on the method of lavender administration and anxiety assessment.

Qualitative analysis showed a significant result in favor of lavender use for anxiety in 54 of 65 included RCTs and 17 of 25 NRSs. However, almost all of the RCTs exhibited a high risk of bias, even when performance bias (when participants change their response because they know which group they are in) was not included as a significant source of bias. Few adverse events were reported and no serious adverse events were reported.

The main results from the meta-analyses, along with effect sizes, are depicted in Figure 3. The first two (of seven) meta-analyses evaluated the influence of Silexan^ ^on anxiety measured by two different methods and demonstrated a favorable effect on anxiety symptoms. Over half of the studies exhibited a high risk of bias and were conducted by the same research team.

Four meta-analyses evaluated the influence of lavender inhalation on three different methods of anxiety assessment and all methods combined. These analyses showed high levels of heterogeneity (except for the physiological measures of anxiety) and most studies had a high risk of bias. Significant results were maintained (albeit with a smaller effect size) when studies with a high risk of bias were removed as a part of a subgroup analysis (only conducted when sufficient trials were included), with the strongest effects in high anxiety inducing situations. Meta-regression analysis identified different study situations (day hospital setting, non-health facility, intensive hospitalization setting, waiting for an invasive procedure in a health facility, and gynecological setting) and dose and duration (single or multi-dose) of lavender exposure as moderators of the effect.

The last meta-analysis found that a massage with lavender essential oil significantly reduced anxiety levels when compared to other physical therapies. A high level of heterogeneity was identified and half of the studies exhibited a high risk of bias.

A favorable effect of lavender administration was identified in most of the studies included in qualitative analysis, but most of the studies also exhibited a high risk of bias. Seven meta-analyses were conducted as a part of the quantitative analysis and demonstrated that lavender administration in the form of Silexan appears to reduce symptoms of anxiety, while inhalation and topical administration of lavender demonstrate potential but need more robust evidence for support. Most RCTs included exhibited a high risk of bias and high levels of heterogeneity.

While this study found that lavender may be used to alleviate symptoms of anxiety, the certainty of its efficacy is still open to question. Studies with standardized practices and better control are needed for a more decisive verdict. Other reviews^[9][10] on lavender report decreases in anxiety symptoms but also cite variability of administration methods and constituents of oil, lack of dose rationale, and short duration of treatment as limitations in the literature and call for standardization of practices. The methods of administration, dosage, duration of use, and study situation will likely influence the effect.

The biggest limitations of the study at hand are the quality and heterogeneity of the available evidence. This can be attributed to the difficulty of masking the easily recognizable odor of lavender, broad range of lavender inhalation methods and dose/duration, and study population characteristics and situations. Nonetheless, even after the removal of performance bias from the risk of bias assessment, most of the studies still had a high risk of bias, indicating poor study reporting standards and various methodological issues. In view of the previously mentioned problem of blinding, one study found that the expectation of lavender^[11] aromatherapy, in comparison to expectations of tea tree aromatherapy or no treatment, impacted measures of relaxation (galvanic skin response), while aromatherapy itself did not. This suggests that the placebo effect plays a non-negotiable role in the outcome of lavender inhalation studies.

The seemingly more robust results in favor of the orally administered lavender supplement Silexan have the bias of being predominantly conducted by the same research group which also reported various conflicts of interest, including ties to and funding from drug companies, which would also explain the low levels of heterogeneity. However, outside of the study under review, various studies have demonstrated the efficacy of Silexan for anxiety. A study by a separate research group that administered Silexan daily at a dose of 160 milligrams for a minimum of eight weeks\ found a reduction of 5-HT1A receptor binding^[12] in healthy participants, when compared to placebo administration. This sort of activity is similar to the mechanism of action shared by anxiolytic and antidepressant drugs like selective reuptake inhibitors (SSRIs). In fact, a recent network meta-analysis^[13] found that an 80 milligram dose of Silexan was equally as effective as paroxetine (an SSRI) at reducing anxiety scores, while a 160 milligram dose was even better. Another study^[14] found Silexan to be comparable to treatment with lorazepam (a benzodiazepine, commonly used to treat anxiety) for generalized anxiety disorders.

Given the potential for beneficial effects and a lack of safety concerns, there seems to be no harm in trying lavender administration to help alleviate anxiety. However, keep in mind^[9] the limitations discussed regarding dosage and duration, as some topical applications have been associated with contact dermatitis^[15], although it is relatively uncommon, and that the FDA has not endorsed lavender for the management of anxiety disorders.

The influence of oral administration of lavender on anxiety is seemingly comparable to current drug treatments (SSRIs and benzodiazepines), but inhalation and topical administration need more rigorous evidence to suggest a meaningful effect beyond expectation. The biggest limitations of the study at hand were a high risk of bias and high level of heterogeneity across studies. There seems to be no harm in oral intake or inhalation of lavender, but a few cases of contact dermatitis following topical administration have been documented.

Q. Assuming the effects found here are accurate, how much does lavender affect anxiety?

This is a tough question to answer. Even assuming that the discussed effects are accurate, there’s still the problem of high heterogeneity—the studies that went into each meta-analysis were usually very different from each other, and the effect of lavender probably varies depending on the situation, dose, dosage form, and type of anxiety.

Generally, lavender has a roughly small to medium effect on anxiety, if the results from the study under review are to be trusted. For example, this study^[16] examining orally administered Silexan in people with restlessness and sleep disturbance found that SIlexan dropped anxiety three more points on the Hamilton anxiety rating scale than placebo, on average. This is a small, and barely statistically significant, difference. On the other hand, consider massaged lavender oil’s effect size in Figure 3. The standardized mean difference is around 0.6-0.7, which cashes out to what is usually considered a medium effect size.

Q. Is there a specific species of lavender that has more active constituents?

Lavender is a plant from the Lamiaceae family that includes various different species. Most lavender species share similar^[17] major chemical constituents, consisting of terpenes, alcohols, ketones, and polyphenols. While constituents and properties are similar among species, lavender essential oil^[18] extracts can range from 26-57% linalool and 4-35% linalyl acetate, with linalool considered the primary active constituent^[4].

Q. What other things might lavender be helpful for?

Beside inducing relaxation, lavender is traditionally known for^[10] treatment of parasitic infections, burns, insect bites, and spasms. Lavender oil might be anti-fungal^[19], reduce headache severity^[20] and hair loss^[21], improve wound healing^[22], and alleviate premenstrual symptoms^[23]. However, as with the studies on anxiety, much more research is needed to really determine an effect.

Q. Does lavender cause gynecomastia?

While the link is not very clear... maybe. Three case studies of prepubertal gynecomastia^[24] have previously been attributed to topical administration of a cologne with lavender^[25] as an ingredient. More recently, a study^[26] reported three prepubertal girls and one boy with clinical evidence of estrogenic action associated with a history of using lavender-based fragrance. While the precise development of these conditions can be multifactorial, the gynecomastia resolved once the use of the products was discontinued and there is in vivo evidence^[24] of estrogenic and antiandrogenic properties of both lavender and tea tree essential oils.

This systematic review and meta-analysis evaluated the effect of lavender administration on anxiety and included 65 RCTs and 25 NRSs for qualitative analysis and 37 RCTs for quantitative analysis. In all analyses, lavender showed an overall improvement in anxiety, but most studies exhibited a high risk of bias and RCTs demonstrated a high level of heterogeneity. Oral administration showed the most robust results due to a standardized extract and dose and even demonstrated comparable results to existing drug treatment for anxiety (SSRIs and benzodiazepines) without the adverse side effects. To determine the efficacy of inhalation and topical administration, researchers will need to standardize methods and the optimal dose/duration of exposure, in addition to conducting higher quality studies.