Effect of Lemongrass Aroma on Experimental Anxiety in Humans

Abstract

Objectives:

The objective of this study was to evaluate the potential anxiolytic effect of lemongrass (Cymbopogon citratus) aroma in healthy volunteers submitted to an anxiogenic situation.

Design:

Forty male volunteers were allocated to four different groups for the inhalation of lemongrass essential oil (test aroma: three or six drops), tea tree essential oil (control aroma: three drops), or distilled water (nonaromatic control: three drops). Immediately after inhalation, each volunteer was submitted to an experimental model of anxiety, the video-monitored version of the Stroop Color-Word Test (SCWT).

Outcome measures:

Psychologic parameters (state anxiety, subjective tension, tranquilization, and sedation) and physiologic parameters (heart rate and gastrocnemius electromyogram activity) were evaluated before the inhalation period and before, during, and after the SCWT.

Results:

Individuals exposed to the test aroma (three and six drops), unlike the control groups, presented a reduction in state anxiety and subjective tension, immediately after treatment administration. In addition, although they presented an anxious response to the task, they completely recovered from it in 5 min, unlike the control groups. Physiologic alterations along the test were not prevented by any treatment, in the same way as has previously been observed for diazepam.

Conclusions:

Although more investigations are necessary to clarify the clinical relevance of lemongrass essential oil as an anxiety treatment, this work shows that very brief exposure to this aroma has some perceived anxiolytic effects.

Introduction

Anxiety, as a symptom or as a disorder, is the most prevalent psychiatric problem in the general population.¹ Nevertheless, its treatment remains a challenge, as the drugs used for the relief of its symptoms can present significant side-effects, promote therapeutic dependence, or have a delayed onset of action.² In addition, not all patients benefit from the available treatments and only a few of them reach complete recovery.^3,4

These facts have justified a growing demand for alternative or complementary procedures for the relief of anxiety symptoms, both by health professionals and the general population.^5,6 Among these procedures is aromatherapy, which is the use of essential oils for therapeutic purposes.⁷

A fairly recent literature review, covering studies from the last 20 years, considered aromatherapy the most commonly used modality of alternative medicine to treat people with anxiety symptoms, with positive results and without adverse effects.⁸ This conclusion suggests that, although further studies are required, aromatherapy could be promising for the treatment of some anxiety disorders.

Controlled clinical studies to evaluate the effect of essential oils in anxiety symptoms are gradually appearing in the literature. Lehrner et al.⁹ showed that patients exposed to sweet orange aroma (Citrus sinensis essential oil), diffused in a waiting room before a dental procedure, showed lower levels of anxiety than control patients, only exposed to atmospheric air. More recently, it was demonstrated that the same aroma, administered through a surgical mask, was able to prevent performance-related anxiety in subjectively healthy volunteers submitted to a human experimental model of anxiety.¹⁰

Animal studies, which eliminate the subjectivity of aromatherapy, have also demonstrated the anxiolytic action of various aromas such as rose,¹¹ lemon,¹² sweet orange,¹³ and lavender.¹⁴ These findings reinforce the idea that the essential oils may have anxiolytic effects per se, not related to massage or to the influence of previous experience with the aromas used nor to the relationship between the patient and the therapist, which some authors^15,16 have suggested could account for the results of aromatherapy.

This state of affairs justifies further studies designed to verify the therapeutic efficacy of aromatherapy in treating anxiety, since simply disregarding this type of therapy, because of its lack of scientific support, might be depriving patients of an effective treatment.

Among the essential oils that are already used by aromatherapists as tranquilizers is lemongrass (Cymbopogon citratus),¹⁷ which has had its acute anxiolytic action demonstrated in mice after oral administration.^18,19 Although the effects of its inhalation have not been evaluated in animals, the possible anxiolytic activity of the C. citratus aroma could readily be tested in humans, as it is generally regarded as safe.²⁰

Bringing all this into consideration, the aim of this work was to evaluate the potential anxiolytic effect of the inhalation of lemongrass essential oil (C. citratus) in healthy volunteers submitted to an anxiogenic situation. Furthermore, to determine the main components of the essential oils administered, a gas chromatography/mass spectrometry (GC/MS) analysis was also carried out.

Materials and Methods

Participants

Forty male, graduate student volunteers, subjectively healthy, aged between 18 and 30, were selected for inclusion in the study by means of a structured clinical questionnaire, a translated and adapted version of the State-Trait Anxiety Inventory (STAI)–Part II²¹ and a translated and adapted version of the Social Phobia Inventory (SPIN).²² Individuals possibly presenting pathologies that could interfere with the results, such as asthma, olfactory problems, psychiatric disorders, or chronic drug use, and individuals with STAI-trait scores above 48 points and/or SPIN scores above 19 points, were excluded.

This study was conducted with approval from the Ethics Committee in Research with Humans of the Universidade Federal de Sergipe, Brazil. Written informed consent was obtained from all participants.

Anxiogenic condition

The video-monitored Stroop Color-Word Test (SCWT), as standardized by Teixeira-Silva et al.,²³ was used to elicit anxiety in the volunteers. This test consists of presenting a board to the participant with 100 of the color-naming words blue, yellow, red, green, and violet organized randomly in a 10 × 10 matrix. Each word is printed in a color different from its meaning (e.g., the word “red” printed in yellow ink). To perform the task, the subject has to say, as quickly as possible and in the sequence presented, the names of the colors being seen (i.e., the color of the ink), but not the colors designated by the words. The task has to be performed in 2 min (maximum), and any errors are signaled with a bell. Skipping a color sequence, hesitation in saying the color, and saying the color's “word” instead of its “ink” are all considered to be errors.

The whole test is videoed and presented to the subject on a monitor during the test. Instructions were given to the subject using a CD recording, which led them to believe that a group of professionals, located in another room, were observing them and would evaluate their performance. The video was not recorded.

Psychologic measurements

State-Trait Anxiety Inventory

This instrument²⁴ is divided into two sections, each having 20 questions. The first subscale measures state anxiety and the second measures trait anxiety. The range of scores, for each subscale, is 20–80; the higher the score, the higher the anxiety. A validated Portuguese version of STAI was used.²¹ A cutoff score for high trait anxiety was derived from Gama et al.²⁵; it provides normative data for male university students from the city. The mean anxiety score for this normative group was 39.6, and the standard deviation (SD) was 9.2. The cutoff between high and medium trait anxiety was set 1 SD above the mean, with the result that scores greater than 48 were classified as high anxiety and, therefore, met the exclusion criteria.

Social Phobia Inventory

The SPIN²⁶ consists of 17 items measuring the following: (1) fear in social situations, (2) avoidance of performance or social situations, and (3) physiologic discomfort in social situations. These items are evaluated on a five-point Likert scale (0–4). Thus, the range of the summed score is 0–68. A validated Portuguese version of SPIN was used.²² A cutoff score of 19 distinguishes between those with social phobia and nonanxious controls.²⁶

Self-evaluation of tension level

The assessment of subjective tension level of the volunteers was made through a numerical scale from 0 (totally relaxed) to 10 (extremely tense).

Visual analog mood scale

This scale²⁷ is composed of 16 pairs of opposite adjectives. Each pair is separated by a 10-cm line on which the subject is requested to mark the point that best represents his feelings. The 16 items are distributed into four categories: (1) mental sedation (alert/drowsy, muzzy/clearheaded, mentally slow/quick-witted, attentive/dreamy); (2) physical sedation (strong/feeble, well coordinated/clumsy, lethargic/energetic, incompetent/proficient); (3) tranquilization (calm/excited, contented/discontented, troubled/tranquil, tense/relaxed), and (4) other feelings and attitudes (happy/sad, antagonistic/amicable, interested/bored, withdrawn/gregarious). The range of values, for each factor, is 0–40 cm. A Portuguese version, translated and validated by Zuardi and Karniol²⁸ and adapted by Del Porto et al.,²⁹ was used.

Physiologic measures

Electromyogram of the gastrocnemius muscle

This was derived from two Ag/AgCl electrodes placed on the gastrocnemius muscle (part of the fight/flight response) of the nondominant leg.

Heart rate

This was derived from two active Ag/AgCl electrodes placed across the chest and one ground Ag/AgCl electrode placed on the abdomen.

The skin was cleaned with a mixture of alcohol/ether (90:10, v/v) before placement of the electrodes.

These recordings were made using a computerized monitoring system of physiologic responses (I-330-C2+ Physiological Monitoring System; J&J Engineering).

All tests were performed in a quiet room maintained at a temperature between 23°C and 25°C (73.4°F and 77.0°F).

Treatments

Test aroma

Essential oil of lemongrass (C. citratus; BioEssência^®), three or six drops (CC₃ or CC₆).

Control aroma

Essential oil of tea tree (Melaleuca alternifolia; BioEssência^®), three drops (MA).

Nonaromatic control

Distilled water, three drops (H₂O).

All treatments were administered by inhalation. Each drop corresponded to 25 μL placed on a paper tissue, which the volunteer was instructed to position in front of his nose.

A randomized double-blind design was followed. For this, a random distribution of the subjects to the experimental groups (n = 10) was made using a draw by a researcher who had no direct participation in the test sessions. In addition, the volunteers were told that they would be inhaling nontoxic substances extracted from plants, which might or might not have a smell. The term “aromatherapy” was never used. A control aroma, proven not to change anxiety levels,¹⁰ was used to confirm that the observed results were not due to unspecific effects of any aroma.

Throughout the entire study, the volunteers were kept ignorant of the therapeutic use of the essential oils being evaluated and about the real purpose of the Stroop test, which was to induce anxiety. Therefore, even if some volunteers could recognize the lemongrass smell, they had no idea how the aroma was supposed to affect their performance in the test.

It is worth mentioning that both of the essential oils used are considered to be safe. C. citratus oil is on the U.S. Food and Drug Administration's GRAS (Generally Regarded as Safe) List,²⁰ while tea tree oil is generally considered to be nontoxic and nonirritant, although it may cause sensitization in some individuals.³⁰

Procedure

The selected volunteers attended the laboratory on two consecutive days. The first day was used for adaptation and the second day for the actual test.

Adaptation day

The subjects were taken to the experiment room, which was already organized and equipped with the necessary apparatuses for the execution of the test, with a maintained temperature between 23°C and 25°C. Subsequently, the subjects were submitted to the psychologic evaluations and then to 5 min of physiologic recordings.

Test day

The subjects were again taken to the experiment room, where they rested for 5 min, after which the adaptation procedure from the first day was repeated. The psychologic and physiologic data collected were labeled as the “Pretreatment” experimental phase. Subsequently, the volunteers were conducted to another room to receive one of the four treatments (CC₃, CC₆, MA, or H₂O). In this study, they watched a researcher pick up one of three identical amber flasks, identified as A, B, or C, and pipette 75 or 150 μL of its contents onto a paper tissue, which they were instructed to position in front of their nose (about 1 cm distant) and to then take three deep breaths. After the inspirations, the paper tissue was placed into a sealed container and taken out of the room. The volunteers then waited for 3 min, during which they answered the following questions: (1) Could you smell anything on the tissue paper? (2) What score, from 0 to 10, would you give to the intensity of the smell, 0 representing the complete absence of smell and 10 representing the most intense smell you've ever felt? (3) What score, from 0 to 10, would you give to your familiarity with the smell, 0 representing a totally unknown smell and 10 representing the absolute knowledge of the smell? and (4) What score, from 0 to 10, would you give to the hedonicity of the smell, 0 representing an extremely unpleasant smell, 10 representing an extremely pleasant smell, and 5 representing neutrality (not pleasant nor unpleasant). They were then taken back to the experiment room and submitted to the anxiogenic condition as follows. Immediately before being given the test instructions, the participant was submitted to psychologic and 30 sec of physiologic evaluations. The data were labeled as the “Before” experimental phase. After listening to the recorded instructions, the participant then performed the task, during which his physiologic measurements were recorded. After 50 words, a pause was made for a second set of psychologic evaluations. These new data were labeled as the “During” experimental phase. Immediately following the evaluations, the test restarted and continued up to the last color or until the end of the scheduled time. The participant then rested for 5 min, after which all the psychologic and physiologic parameters were again evaluated. The final set of data was labeled as the “After” experimental phase.

For a flow chart of the test day procedures, see Figure 1.

FIG. 1.

Schematic diagram of the test day procedures. SCWT, the video-monitored Stroop Color-Word Test.

GC/MS analysis of the essential oils

A GC/MS analysis was performed as described in a previous paper.¹³

Statistical analysis

The data collected during the adaptation phase were not analyzed as this phase was only intended to habituate the participants to the environment and apparatuses that would be used on the following day.

All the psychologic data (ordinal scale) obtained during the test were analyzed by Friedman's analysis of variance (ANOVA), per treatment group, for each studied parameter, followed by Tukey's type test for post hoc comparisons, when appropriate.

All the physiologic data (ratio scale) obtained were analyzed using a two-factor ANOVA for repeated measures followed by Tukey's test for post hoc comparisons.

The STAI Trait and SPIN scores used in the selection process were analyzed by Kruskal–Wallis ANOVA.

The intensity, familiarity, and hedonicity of the aromas were also compared by Kruskal–Wallis ANOVA.

All significance tests were two tailed and were performed at a 5% significance level.

Results

Aroma perception

The aroma perception scores obtained for each treatment group are shown in Table 1.

Table 1.

Aroma Perception

	Aroma perception scores
Treatment	Intensity (How intense was what you smelled?)	Familiarity (Can you identify what you smelled?)	Hedonicity (Did you find the smell pleasant, unpleasant, or neither?)
CC₃	6.5 (6.0–7.0)	8.5 (7.25–9.0)	8.0 (7.0–8.0)
CC₆	7.0 (7.0–7.0)	8.0 (6.25–8.0)	6.5 (6.0–7.0)
MA	7.0 (6.0–8.0)	6.0 (4.0–7.5)	6.0 (5.0–7.0)
H₂O	1.0 (1.0–2.0)	0.0 (0.0–1.0)	5.0 (5.0–5.0)

Data are presented as median and interquartile range (Q ₁–Q ₃). CC₃ and CC₆ represent essential oil of Cymbopogon citratus three and six drops. MA, essential oil of Melaleuca alternifolia. Intensity scores: ranging 0 to 10, 0 representing the complete absence of smell and 10 the strongest smell. Familiarity scores: ranging 0 to 10, 0 representing a totally unknown smell and 10 absolute knowledge. Hedonicity scores: ranging 0 to 10, 0 representing an extremely unpleasant smell, 10 representing an extremely pleasant smell, and 5 representing a neutral smell (neither pleasant nor unpleasant).

The ANOVA revealed no significant differences among the treatment groups regarding intensity (p = 0.45), familiarity (p = 0.70), or hedonicity (p = 0.10) of the aromas.

In the groups CC₃, CC₆, and MA, all the volunteers said “yes” to the question “Could you smell anything on the tissue paper?” whereas in the group H₂O, only two subjects said “yes” to the same question, both of which attributed score 1 to the intensity, 0 to familiarity, and 5 (not pleasant nor unpleasant) to hedonicity of the aroma.

Psychologic measurements

Data are presented as the median and interquartile range (Q ₁–Q ₃).

ANOVA results are described here, while post hoc results are shown in Table 2.

Table 2.

Summary of the Psychologic Results

		Experimental phase
Parameter	Treatment	Pretreatment	Before	During	After
STAI-state (points)	CC₃	31.5 (37.2–33.7)	29.5 (26.5–33.5)^a	38.5 (35.3–42.7)^b	31.0 (28.2–37.2)^{b c}
	CC₆	32.0 (31–36.2)	32.0 (30.2–34.7)^a	35.5 (34–41.2)^b	32.5 (31–33.7)^c
	MA	33.0 (31.0–35.5)	34.5 (28.0–39.2)	42.5 (34.5–49.7)^b	35 (28.2–42.0)^{b c}
	H₂O	32.5 (29.5–35.2)	32.5 (29–34.7)	36.5 (31.5–42.0)^b	33.0 (29.5–40.0)^{b c}
Tranquilization (cm)	CC₃	32.5 (28.4–37.0)	33.2 (32.2–35.0)	21.2 (18.5–26.1)^b	30.3 (26.8–32.3)^{b c}
	CC₆	32.5 (30.7–33.7)	32.7 (29.3–33.4)	27.0 (21.0–30.8)^b	30.3 (28.0–33.1)^{b c}
	MA	33.5 (26.4–35.3)	29.4 (25.6–37.5)	23.8 (28.3–33.1)	27.3 (23.5–34.3)
	H₂O	31.8 (28.8–33.4)	31.2 (27.8–33.8)^a	27.8 (21.3–30.7)^b	29.6 (25–30.9)^{b c}
Mental sedation (cm)	CC₃	15.0 (14.7–18.4)	14.7 (11.6–19.1)	13.7 (6.9–14.6)	9.3 (7.5–14.1)
	CC₆	14.2 (12.7–17.3)	14.2 (11.7–14.8)^a	11.1 (6.6–14.7)^b	12.4 (7.1–14.4)^b
	MA	16.8 (12.1–18.3)	17.0 (13.3–17.3)	15.7 (10.2–17.0)	14.2 (7.8–18.6)
	H₂O	12.8 (6.8–18.7)	7.3 (5.4–12.4)	9.9 (6.3–13.2)	10.5 (5.6–13.3)
Physical sedation (cm)	CC₃	9.8 (8.9–12.7)	13.6 (9.2–14.9)	11.5 (8.1–12.7)	9.8 (7.7–12.7)
	CC₆	12.1 (11–15.6)	11.3 (8.7–14.1)^a	12.8 (6.6–15.3)	10.2 (7.1–11)^{b c}
	MA	14.7 (6.6–17.2)	14.4 (9.6–17.1)	12.2 (5.5–18.9)	12.7 (6.9–15.9)
	H₂O	10.9 (7.5–14.3)	7.6 (4.8–12.8)	7.9 (5.5–10.6)	7.8 (3.5–10.6)
Other feelings and attitudes (cm)	CC₃	7.6 (4.8–12)	7.2 (5.9–10.6)	9.1 (5.6–10.9)	7.1 (4.3–10.7)
	CC₆	8.7 (7.0–12.4)	7.5 (6.0–10.9)	7.0 (5.0–11.3)	7.9 (5.6–11.8)
	MA	10.0 (4.8–15.3)	9.7 (5.8–14.1)	9.8 (7.1–15.0)	9.6 (7.3–14.6)
	H₂O	6.4 (4.1–10.7)	7.4 (4.9–10.9)	5.6 (4.5–10.9)	5.2 (4.2–10.5)
Self-evaluation of tension level (points)	CC₃	3.0 (2.0–3.75)	3.0 (2.0–4.5)	5.0 (4.0–6.0)^b	2.5 (2.0–3.7)^c
	CC₆	2.5 (2.0–3.0)	2.0 (2.0–3.0)^a	4.0 (3.2–4.7)^b	2.5 (2.0–3.7)^{b c}
	MA	2.0 (1.25–3.0)	2.0 (1.2–2.7)	4.0 (2.5–4.8)^b	2.0 (1.25–3.0)^{b c}
	H₂O	2.0 (1.2–2.0)	2.0 (1.0–3.0)	3.0 (2.0–4.7)^b	3.0 (2.0–4.0)^b

Data are presented as median and interquartile range (Q ₁–Q ₃). The treatments in bold are those that showed no significant differences in state anxiety among the experimental phases.

Significantly different from “Pretreatment.”

Significantly different from “Before.”

Significantly different from “During.”

abc

p < 0.05.

STAI, State-Trait Anxiety Inventory.

It is worth pointing out that the treatment's effect is revealed by the lack of significant alterations in the observed parameters throughout the test.

Social Phobia Inventory

Kruskal–Wallis ANOVA found no significant differences in levels of social anxiety (p = 0.80) among treatment groups [ \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document}$\tilde{x}$ \end{document} (Q ₁–Q ₃): CC₃ = 9.0 (7.0–14.0); CC₆ = 13.0 (8.0–17.0); MA = 14.0 (8.3–19.0); H₂O = 12.0 (9.3–13.0)].

STAI-Trait

Kruskal–Wallis ANOVA found no significant differences in trait anxiety levels (p = 0.98) among treatment groups [ \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document}$\tilde{x}$ \end{document} (Q ₁–Q ₃): CC₃ = 35.0 (32.0–38.2); CC₆ = 35.0 (33.0–37.5); MA = 35.5 (33.5–38.2); H₂O = 36.0 (33.0–37.0)].

STAI-State

Friedman's ANOVA revealed significant differences in state anxiety among the experimental phases for all the groups: CC₃ (p < 0.01), CC₆ (p < 0.01), and MA (p = 0.01) e H₂O (p < 0.01).

Tension level

Friedman's ANOVA revealed significant differences in subjective tension level among the experimental phases for all the groups: CC₃ (p < 0.01), CC₆ (p < 0.01), and MA (p = 0.02) e H₂O (p = 0.04).

Visual analog mood scale—mental sedation

Friedman's ANOVA revealed no significant differences among the experimental phases for any of the groups: CC₃ (p = 0.10), MA (p = 0.99), H₂O (p = 0.15), except for CC₆ (p = 0.04).

Visual analog mood scale—physical sedation

Friedman's ANOVA revealed no significant differences among the experimental phases for any of the groups: CC₃ (p = 0.71), MA (p = 0.64), H₂O (p = 0.07), except for CC₆ (p = 0.02).

Visual analog mood scale—tranquilization

Friedman's ANOVA revealed no significant differences among the experimental phases for the group MA (p = 0.11), although differences were found for the groups CC₃ (p < 0.01) and CC₆ (p = 0.02) e H₂O (p = 0.03).

Visual analog mood scale—other feelings and attitudes

Friedman's ANOVA revealed no significant differences among the experimental phases for any of the groups: CC₃ (p = 0.52), CC₆ (p = 0.28), and MA (p = 0.74) e H₂O (p = 0.98).

Physiologic measurements

For each physiologic parameter, data are presented as mean and standard error of the mean in Table 3.

Table 3.

Summary of Physiologic Results

		Experimental phase
Parameters	Treatment	Pretreatment	Before	During	After
Heart rate (beats/min)	CC₃	78.9 ± 10.4	77.1 ± 12.2	106.2 ± 18.0	76.9 ± 10.1
	CC₆	74.2 ± 8.7	72.2 ± 5.6	92.0 ± 13.6	73.3 ± 6.1
	MA	73.4 ± 8.7	71.2 ± 6.6	86.5 ± 14.3	71.6 ± 6.8
	H₂O	70.6 ± 8.7	70.3 ± 10.9	99.2 ± 27.0	71.0 ± 6.5
Electromyogram activity of the gastrocnemius muscle (μV)	CC₃	1.8 ± 1.5	1.8 ± 2.0	3.7 ± 2.2	1.7 ± 1.5
	CC₆	1.4 ± 1.0	1.4 ± 1.5	5.8 ± 5.5	1.3 ± 0.8
	MA	1.9 ± 1.7	2.7 ± 3.2	4.0 ± 3.3	2.1 ± 2.5
	H₂O	2.7 ± 2.0	1.6 ± 1.2	3.4 ± 2.3	2.2 ± 1.3

Data are presented as mean ± standard error of the mean.

Heart rate

Due to technical problems, the HR measurements of two volunteers from the CC₃ group were not recorded and, therefore, were not included in the statistical analysis. The ANOVA revealed no significant interaction between the experimental phase and treatment (p = 0.23), and therefore, the two main effects were individually analyzed. Only the experimental phase effect was significant (p < 0.01), in that the heart rate was greater in the “During” compared to the other experimental phases (p < 0.01).

Gastrocnemius electromyogram activity

The ANOVA revealed no significant interaction between the experimental phase and treatment (p = 0.13), and therefore, the two main effects were individually analyzed. Only the experimental phase effect was significant (p < 0.01), in that the muscular tension was greater in the “During” compared to the other experimental phases (p < 0.01).

GC/MS analysis

The volatile composition of C. citratus and M. alternifolia essential oils is shown in Tables 4 and 5, respectively.

Table 4.

Volatile Composition of C. citratus Essential Oil

Peak	RT (min)	Compounds	%	RI
1	6.422	Triciclene	0.18	921
2	6.748	α-Pinene	0.24	932
3	7.275	Canfene	1.37	946
4	8.425	6-metil-5-hepten-2-one	1.73	981
5	9.950	Limonene	0.27	1,024
6	10.208	Z-β-ocimene	0.26	1,032
7	11.508	NI	1.09	1,070
8	12.550	Linalol	1.00	1,095
9	14.350	NI	0.16	1,148
10	14.833	Z-isocitral	0.56	1,160
11	15.217	Borneol	0.19	1,165
12	15.533	E-isocitral	1.34	1,177
13	17.675	Neral	31.49	1,235
14	18.108	Geraniol	6.00	1,249
15	18.775	Geranial	41.84	1,264
16	22.608	Geranyl acetate	9.04	1,379
17	23.983	(E)-Caryophyllene	1.68	1,417
18	27.050	γ-Cadinene	1.13	1,513
19	27.208	δ-Cadinene	0.43	1,522
		Total	100

Obs.: Geranial and neral together form citral, which corresponds to 73.33% of the essential oil.

RT, retention time; RI, retention index; NI, nonidentified compounds.

Table 5.

Volatile Composition of M. alternifolia Essential Oil

Peak	RT (min)	Components	%	RI
1	6.575	α-Tujene	0.58	924
2	6.800	α-Pinene	2.17	931
3	8.208	β-Pinene	0.55	976
4	8.600	Myrcene	0.65	988
5	9.550	α-Terpinene	6.97	1,016
6	9.825	p-Cymene	5.30	1,024
7	9.983	Limonene	1.02	1,027
8	10.100	1,8-Cineole	4.31	1,031
9	11.050	γ-Terpinene	17.69	1,058
10	12.017	Terpinolene	2.76	1,084
11	15.633	Terpinen-4-ol	49.83	1,082
12	16.108	α-Terpineol	3.79	1,194
13	23.992	(E)-Caryophyllene	0.37	1,417
14	24.617	Aromadendrene	1.19	1,437
15	25.325	Alloaromadendrene	0.49	1,458
16	26.350	Viridiflorene	0.59	1,489
17	26.500	NI	0.37	1,494
18	27.217	δ-Cadinene	0.95	1,517
19	29.350	Globulol	0.42	1,585
		Total	99.26

Discussion

The aim of this work was to evaluate the potential anxiolytic effect of lemongrass (C. citratus) essential oil aroma in healthy volunteers submitted to an anxiogenic situation.

The choice of C. citratus doses administered to the volunteers was based on practical aromatherapy, in which therapists recommend amounts ranging from three to six drops and exposure time ranging from three breaths to a few minutes.^17,31

Regarding the psychologic measurements, the lemongrass aroma was not able, at any dose, to prevent the increase in anxiety caused by the SCWT. However, for both CC₃ and CC₆ groups, STAI-state scores in the experimental phase “Before” were lower than at “Pretreatment,” indicating that the aroma was able to reduce the basal level of anxiety. In addition, for the CC₆ group, the experimental phase “After” was not different from “Before,” showing that under the influence of six drops of lemongrass essential oil, individuals presented a complete involution of the anxious response, in 5 min, which did not occur with the other groups. This demonstrates that the lemongrass aroma is able to accelerate the recovery process of individuals who have been exposed to an anxiogenic situation, although this effect is not common to all doses.

The effect of decreasing basal anxiety, while supported by the result of tension level, was surprising as not even diazepam, a classic anxiolytic agent, when tested on the SCWT, was able to reduce basal anxiety in healthy volunteers, although it was able to prevent the anxious peak during the test.²³ This same profile of action was presented by the sweet orange aroma.¹⁰

It is possible that the lemongrass aroma is acting in different neuroanatomical substrates and/or neurotransmitter systems than those in which occurs the action of benzodiazepines. The fact that this aroma was able to reduce basal anxiety and accelerate the reversion of reactive anxiety, without reducing its intensity, suggests that it is acting in an anxiety neural pathway as a reversible antagonist, or as an autoreceptor agonist, or by increasing the degradation rate of a neurotransmitter, while diazepam activates a GABAergic circuit, inhibitory of this same pathway.

It is tempting to speculate that the pathway in question would be serotonergic due to the role of serotonin in anxiety. Following this train of thought, the lemongrass aroma could be acting like the bitter orange essential oil,³² as a 5-HT_1A autoreceptor agonist. Having said that, it is important to mention that the involvement of the GABAergic system in the anxiolytic effect of lemongrass essential oil orally administered to mice has been demonstrated,¹⁹ but it is possible that different administration routes result in different mechanisms of action. Future investigations should address these questions.

In this study, the essential oil was administered through the respiratory system, which consists of three routes: (1) olfactory pathway, through which the aroma can directly excite olfactory receptors, leading to an electrophysiologic response that directly reaches the limbic system³³; (2) nose-to-brain pathway, through which intranasally administered substances can reach the central nervous system, by either crossing the cribriform plate through diffusion among the fibers of the olfactory nerve or by penetrating the olfactory cells and being transported by them to the olfactory bulb³⁴; and (3) the inhalation pathway, in which the inhaled active molecules of the essential oil can fall into the circulation and reach the central nervous system.³⁵ Due to the immediate effect observed after only three deep breaths, it is more likely that the action of the lemongrass aroma was given through the olfactory pathway or through the diffusion mechanism of the nose-to-brain pathway.

It is important to emphasize, however, that the experiment presented here was not intended to clarify the mechanism of action of the essential oil of C. citratus. Further studies, designed specifically for this purpose, should be performed. Nevertheless, these results demonstrate that the lemongrass aroma, although not capable of preventing an anxious response, is effective in reducing the already installed anxiety, restoring homeostasis.

Interestingly, besides decreasing the basal level of anxiety and accelerating the reversion of the anxious response, the highest dose of C. citratus made the volunteers feel more awake, according to the visual analog mood scales' results (mental and physical sedation items), which is exactly the opposite of what is observed for most anxiolytic drugs that are sedative in high doses. A similar result was observed for the sweet orange aroma,¹⁰ suggesting that anxiolytic essential oils exhibit some advantages compared to classic anxiolytic drugs. At this point, it is worth drawing attention to the fact that, although the two doses of C. citratus tested here presented anxiolytic activity, the highest one (six drops) has a wider range of desirable effects: it reduces basal anxiety, which is important for anxiety disorders' patients; it reverts reactive anxiety, which is interesting to anybody who has been through an anxiogenic experience; and it increases perceived alertness.

Regarding the physiologic parameters, there was no prevention of the stress response to the SCWT, in any of the treatment groups. However, this result does not weaken the case for the lemongrass aroma as an anxiety reducer, since even diazepam is unable to prevent physiologic alterations induced by anxiogenic situations.²³

Finally, analysis by GC/MS showed that the major component of the studied oil is citral (73.33%), followed by minor components, such as geranyl acetate, camphene, and linalool. This is an important point since, depending on its variants, the essential oil of C. citratus may have roughly equal amounts of myrcene and citral (East Indian variant) or little myrcene and a high amount of citral (West Indian variant).³⁶ These different chemical types may not have the same effects. In fact, it has been demonstrated that the anxiolytic effect of C. citratus essential oil, orally administered, only appears when there is a predominance of citral,¹⁸ although this terpene, when isolated, does not seem to affect anxiety parameters.³⁷ Thus, it is possible that citral is necessary, but not sufficient, for the anxiolytic effect of the lemongrass aroma.

Conclusions

In conclusion, although more investigations are necessary to clarify the clinical relevance of C. citratus essential oil as an anxiety treatment, this work shows that very brief exposure to this aroma has some perceived anxiolytic effects.

Footnotes

Acknowledgments

This work was supported by Fundação de Apoio a Pesquisa e à Inovação Tecnológia do Estado de Sergipe (FAPITEC/SE) and by a grant to Tiago Costa Goes from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). The authors thank their friend Christopher Lloyd for his assistance in writing the English version of this paper.

Author Disclosure Statement

No competing financial interests exist.

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