A Brief Review of Current Scientific Evidence InvolvingAromatherapy Use for Nausea and Vomiting

Pei Lin Lua, PhD, and Noor Salihah Zakaria, BSc

Abstract

Objectives: The objective of this study was to compile existing scientific evidence regarding the effects ofessential oils (EOs) administered via inhalation for the alleviation of nausea and vomiting.Methods: CINAHL, PubMed, and EBSCO Host and Science Direct databases were searched for articles related tothe use of EOs and/or aromatherapy for nausea and vomiting. Only articles using English as a language ofpublication were included. Eligible articles included all forms of evidence (nonexperimental, experimental, casereport). Interventions were limited to the use of EOs by inhalation of their vapors to treat symptoms of nauseaand vomiting in various conditions regardless of age group. Studies where the intervention did not utilize EOsor were concerned with only alcohol inhalation and trials that combined the use of aromatherapy with othertreatments (massage, relaxations, or acupressure) were excluded.Results: Five (5) articles met the inclusion criteria encompassing trials with 328 respondents. Their resultssuggest that the inhaled vapor of peppermint or ginger essential oils not only reduced the incidence and severityof nausea and vomiting but also decreased antiemetic requirements and consequently improved patient satis-faction. However, a definitive conclusion could not be drawn due to methodological flaws in the existingresearch articles and an acute lack of additional research in this area.Conclusions: The existing evidence is encouraging but yet not compelling. Hence, further well-designed largetrials are needed before confirmation of EOs effectiveness in treating nausea and vomiting can be stronglysubstantiated.

Introduction

Nausea and vomiting are symptoms that can be causedby various diseases and certain life events such as

pregnancy.1 Depending on the underlying pathogenesis,these symptoms may appear in acute or chronic form. Nauseais defined as an unpleasant sensation around the throat, uppergastric region, or abdomen or commonly described as feeling‘‘sick to the stomach.’’2 Vomiting or emesis can be denoted as‘‘throwing up’’ (the forceful expulsion of the stomach contentsthrough the oral or nasal cavity).2 The frequent number ofoccurrences of nausea and vomiting sometimes cause thesesymptoms to be regarded as inconvenient or a nuisance ratherthan being seen as a medical problem. Failure to address thefocal issues of these symptoms can be debilitating, causingunnecessarily prolonged recovery times, and may eventuallylead to serious complications such as pneumonia, dehydra-tion, and malnutrition.3

To date, the main pharmacological intervention for nauseaand vomiting involves antiemetic prescription. Considerable

progress has been made in antiemetic therapy, particularlywith the use of a 5-HT3 receptor antagonist, a highly effectiveantiemetic, particularly beneficial for high-risk patients,especially chemotherapy and radiotherapy recepients.4

Nevertheless, despite the availability of this modern treat-ment, nausea and vomiting remain among the most commonsymptoms experienced by a large number of patients inmedical conditions such as postoperative, chemotherapy,and radiotherapy recipients, with the reported incidencereaching to over 50% of the populations.5–7 Self-care reme-dies such as drinking ginger or peppermint teas, eating blandfoods, and relaxation have been commonly attempted, es-pecially for temporary or mild nausea and vomiting.3,8 Un-fortunately, nausea and vomiting can also impose negativeimpacts on the quality of life (QoL),9 thus warranting greaterattention to improve patients’ health outcomes. With anemphasis on improvements in current practices along withthe increasing demand for holistic care, the integration ofcomplementary therapies into mainstream treatment mayhelp to achieve desirable patient outcomes.

Centre for Clinical and Quality of Life Studies, Faculty of Medicine and Health Sciences, Universiti Sultan Zainal Abidin, Terengganu,Malaysia.

THE JOURNAL OF ALTERNATIVE AND COMPLEMENTARY MEDICINEVolume 18, Number 6, 2012, pp. 534–540ª Mary Ann Liebert, Inc.DOI: 10.1089/acm.2010.0862

534

Aromatherapy refers to the therapeutic use of fragrantsubstances, called essential oils (EOs), to help improvephysical and mental health and QoL10 and represents apossible form of complementary and alternative medicine(CAM) for nausea and vomiting. EOs are usually obtainedby steam distillation of aromatic plants,11 whereas otherkinds of extracts that are not obtained by steam distillationare not considered as EOs.12 Different aromatic plants pro-duce EOs with different fragrance and therapeutic charac-teristics depending on their chemical constituents.13 Forexample, lavender (Lavandula angustifolia) and its main con-stituents, linalyl acetate and linalool, exhibit local anestheticeffects in animal in vitro models.14 Additionally, in otheranimal studies, a-bisabolol from chamomile (Matricaria re-cutita) EOs was identified as having strong anti-inflamma-tory effects.15 The main therapeutic properties of EOs alsoinclude antiseptic, antibacterial, wound-healing, immune-stimulant, as well as calming, sedative, analgesic, uplifting,and stimulating effects.16

For thousands of years, aromatherapy has been used incountries such as Egypt and India as an ancient tradition ofherbal medicine.17 Aromatherapy could be applied eitherthrough inhalation of fragrances, topical application (withor without massage enhancement), or both. In France, thepractice of medical aromatherapy involves internal use (in-gestion) of EOs15 such as the consumption of peppermint(Mentha piperita) oils for gastrointestinal disorders to reducecolonic spasm during colonoscopy18 and the symptoms ofirritable bowel syndrome.19 Other than that, EOs can also bediffused in the air, added in the warm bath water, or used inplant poultices or compresses. However, for the purpose ofthis review, the focus is on the therapeutic use of EOs pri-marily via inhalation of its vapors. Due to its advantage ofbeing a noninvasive and relatively low-risk treatment, aro-matherapy could serve as a promising modality to improvepatient care.20 However, with the advances of evidence-based medicine, empirical research is consistently required toevaluate the efficacy of this treatment modality. For the timebeing, substantial evidence for clinical trials on aromather-apy is limited to relaxation alone.15

Despite the limited clinical evidence, there are encourag-ing indications from basic science research that certain EOvapors are absorbed by inhalation and alter brain func-tion.21–23 Herz24 proposed two hypothetical mechanisms forthe effects of odors on mood, behavior, and physiology:pharmacologic and psychologic mechanisms. Pharmacolo-gically, the fragrances of EOs may deliver direct effects onthe central/ autonomic nervous system and endocrine sys-tem regardless of conscious evaluation. Following inhalation,volatile EO molecules pass to olfactory receptors in the nose,which recognize their molecular characteristics, and sendsignals to the brain via the olfactory nerve. In addition, someof the constituents pass into the bloodstream via the lungsand consequently produce their effects directly on brainneurons after passing through the blood–brain barrier.25

Apart from that, based on psychologic hypothesis, the po-tential effects of smell depend on emotional learning, con-scious perception, as well as belief and expectations. As such,the perceived quality of the odors is also accountable for theindividual responses.

Although aromatherapy represents the most regularlypracticed CAM modality by users, it is also one of the least-

researched therapies. At the present time, there are no re-views for aromatherapy on the Cochrane database.26 A newreview is in process as a team is updating the review andpreparing a protocol to evaluate the effectiveness of aroma-therapy for postoperative nausea and vomiting26 (this wasalso confirmed through personal communication with themain author). As such, the objective of the current review isto compile the currently available scientific evidence on theeffects of aromatherapy for nausea and vomiting.

Methods

The authors sought to identify all clinical trials and re-views involving the therapeutic use of inhaled aromatherapyto alleviate nausea and vomiting. Eligible articles included allforms of evidence (nonexperimental, experimental, case re-port). Interventions were limited to the use of EOs by vaporinhalation to treat symptoms of nausea and vomiting invarious conditions regardless of age group. Studies wherethe intervention did not utilize EOs or were concerned withonly alcohol inhalation and trials that combined the use ofaromatherapy with other treatments (massage, relaxations,or acupressure) were excluded. An inclusive search forclinical research was carried out in major biomedical, nurs-ing, and specialist CAM databases such as CINAHL,PubMed, EBSCO Host, and Science Direct. The search en-compassed all articles published by the end of November2010. The basic search terms used included aromatherapy,essential oils, scent, fragrance, nausea, vomiting, and com-plementary therapy. In order to obtain the widest range ofstudies, no limit was set for the date of publication. In ad-dition, the bibliographies of the located studies were scannedfor further relevant studies. Nevertheless, only articles usingEnglish as a language of publication were included in thisreview. Further information on unpublished and ongoingresearch was traced using relevant databases such as Clin-icaltrials.gov (US). Figure 1 shows the flow of the literaturesearch process.

Results

All reviewed studies are summarized in Table 1. Thesearches identified four clinical studies and one review articleinvolving a total of 328 study participants. Three (3) studiesinvestigated postoperative nausea and vomiting (PONV) andone study focused on oncology nausea and vomiting. Allstudies concluded that inhaled aromatherapy served as aneffective treatment for the nausea and vomiting. Other con-siderations for practical use of aromatherapy included thereduction in antiemetic requirement such as prochlorperazine,droperidol, ondansetron, or metoclopramide, increased pa-tient satisfaction, and improved cost effectiveness.

These studies varied from simple observational studies tothe use of a randomized controlled trial. The outcomesevaluated included PONV and oncology nausea. Visual an-alog scale (VAS), standard descriptive ordinal scale, nauseasection of the Edmonton Symptom Assessment System(ESAS), as well as the reported incidence were the instru-ments used to measure the intended outcomes. In the An-derson and Gross5 trial, a 100-mm VAS was rated by therespondents at 2 and 5 minutes postintervention. A studyby Tate27 collected the information related to nausea on a4-hourly and 12-hourly basis.

AROMATHERAPY FOR NAUSEA AND VOMITING 535

The interventions also differed as evidenced by the use ofa variety of EOs. In two studies, peppermint oil was used fornausea and vomiting treatment in the experimentalgroup.5,27 Specifically in one trial, patients were asked toinhale the vapors deeply through the nose three times from ascented gauze pad held directly under their nostril, then toexhale slowly through the mouth.5 In another study, con-senting patients were also offered peppermint oils that wereadministered through the inhaler for 5 seconds.28 Geiger25

used ginger essential oil in his study in which 5% Zingiberofficinalis (ginger) in grape-seed oil was applied below thenose immediately before surgery. Additionally, the solutionwas put on the pulse-points of both wrists for patients tosniff if they experienced nausea postoperatively. The Stringerand Donald29 trial employed a personalized aromatherapyinhalation device, known as Aromastick, whereby a choice oftwo blends of essential oils was available for patients tochoose. One of the revealed blends consisted of peppermintand lemon (Citrus limonum). This device was held by patientsapproximately 6 inches under their nose while breathing inand it could be used as necessary, allowing self-symptommanagement.

Three (3) studies of controlled trials reported using dif-ferent controls or placebos. Geiger25 and Tate27 comparedtheir aromatherapy intervention to a no-treatment group.Additionally, peppermint essence was also used in the studyby Tate27 in his three-arm evaluations to assess the efficacy ofpeppermint EOs for PONV. Conversely, the respondents inthe Anderson5 trial were provided with placebo gauze padsprepared by placing 2 mL of isotonic saline.

A substantial number of patients had reported the benefitsof using aromatherapy. This was evidenced by 82% of re-spondents indicating the benefits of Aromasticks for nauseamanagement whereby almost half (47%) settled their nauseaproblem.29 Another study also showed that 80% of high-riskpatients did not experience PONV after the application of5% ginger EOs nasocutaneously.25 In addition, self-reported

nausea score was significantly different between the placeboand experimental groups.27 Despite overall nausea scoredecreasing significantly after aromatherapy administration,the reduction was independent of treatment5 attributed tothe favorable effects of controlled breathing patterns.

Discussion

Study outcomes

The overall findings from the reviewed studies suggestthat aromatherapy can offer beneficial effects for nausea andvomiting. However, there are very few published researcharticles as well as apparent methodological flaws on thissubject matter, providing room for improvement. Most of thestudies included had examined the efficacy of aromatherapyon PONV patients, enabling the possibility of evaluating itseffectiveness for various types of clients. However, they wereconfined only to limited sample sizes (n = 17–160) and theirstudy designs were not entirely satisfactory. Difficulties inrecruiting and retaining patients were problems common toall clinical trials due to the use of broad exclusion criteria andinadequate outreach to populations such as individuals withlow income, ethnic minorities, and the elderly.30 This factorwould limit the patient participation and clearly reducegeneralizability. With only one study adopting a randomizedcontrol design,5 attempts to evaluate the actual clinical ben-efit of this complementary therapy remain challenging.

Placebo/control

Selecting the appropriate placebo for aromatherapy in-tervention can be difficult. Wiebe31 suggested that the con-trol for CAM trials should sufficiently mimic activetreatment to support the blinding of patients.32 For instance,the study by Tate27 used a fragrance-matched artificial pla-cebo (peppermint essence) as a comparator, lacking inmenthol composition compared to peppermint EOs. Mostaromatherapists believe that synthetic fragrances are inferiorto EOs, although they are often composed of many of thesame compounds.33 This is because synthetic fragrances lacknatural or vital energy; however, this has been contested byodor psychologists and biochemists who believe in the im-portance of therapeutic odor in treating various illnesses.34

Menthyl acetate, which is responsible for peppermint’sminty aroma and flavor,35 might also be favorable in nauseaconditions. However, because adaptation to the odorant oc-curs quickly (in which the smell receptors become less re-sponsive to respond to repeated or continued stimuli ofconstant odor intensity), this condition reduces the potencyof the odor to treat an ill condition, thus supporting thepharmacologic effects of EOs.34,36 Therefore, the respondentscould be blinded by using peppermint essence, since thesmell was similar except it was devoid of the active thera-peutic compound in peppermint essential oils (menthol).However, an experienced practitioner might be able to dis-tinguish the differences considering the lack in menthol inpeppermint essence, hence moderating its cool sensationproperties. As such, the evaluation on the blinding may givevaluable information, especially in adopting a double-blindstudy design. For instance, Graham et al. 37 revealed thattheir attempts to blind patients for aromatherapy interven-tion were not 100% effective, although most were uncertain

FIG. 1. The flow in the literature search process.

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or wrong about the treatment they actually received.Therefore, it is important for future trials to choose the ap-propriate placebo as well as to conduct the blinding assess-ment in order to minimize (if not eliminate) the placebodetection effect.

Assessment methods

There were no standard and consistent measures to assessnausea and vomiting. Three (3) studies measured the se-verity of nausea either using the VAS, nausea section ofESAS, or a standardized descriptive ordinal scale, whereasanother two studies only reported the incidence of thesymptoms. VAS is commonly used to measure a variety ofsubjective responses including the assessment of ‘‘feeling.’’38

Generally, it consists of a 100-mm-long line in which thelower anchor end corresponds to ‘‘no symptom’’ and thehigher anchor end signifies ‘‘unbearable symptom.’’ Nauseaintensity measurement using VAS serves an advantage overother methods, considering that continuous data have ratioproperties and are well suited for statistical analysis, unlikecategorical scales38 in the nausea section of ESAS or stan-dardized descriptive ordinal scale. This instrument is alsoeasy to be self-administered for the patients because of itssimplicity and speed of completion as well as being unhin-dered by a language barrier.39 However, the estimation ofnausea intensity with VAS requires an ability to transform acomplex subjective experience to a visual–spatial display,which involves perceptual judgment and accuracy. Potentialinvestigator bias might also occur, since patients may requirelengthy instructions from trained staff before completion.Despite these limitations, VAS may still serve as a useful self-reported tool in assessing nausea and vomiting consideringindividual subjective perception of these symptoms.

Essential oils (EOs)

Inconsistencies in terms of the type of EOs and how theywere delivered (including dose, blended or single oil used)hampered comparisons between these studies. Peppermintand ginger oils have been regularly used in the aroma-therapy intervention for nausea, using various methods ofadministration including oral preparations. The selection ofthese EOs was associated with the role of their chemicalconstituents, which help in the relief of gastrointestinalsymptoms.24,26 Peppermint oils have been shown to be aneffective remedy for morning sickness, dyspepsia, and othergastrointestinal complaints; its effectiveness is attributed toits antispasmodic properties.40 In addition, the botanicalform of ginger was often advocated as beneficial for nauseaand vomiting in various conditions including motion sick-ness, pregnancy-induced and postoperative conditions.41-42

On the other hand, aromatherapists particularly use theEOs in a blend form, since they are believed to be moreeffective as the therapeutic value is generated by the reac-tion and balance of the oils’ constituents.33 The evidencefrom the Stringer and Donald29 trial on the effectiveness ofblended EOs to reduce nausea and vomiting is still deba-table, as its retrospective design prevented the exclusionof various study biases. Considering these facts, the im-portant issues mentioned need to be further explored tomaximize the potential benefits of EOs use via inhaledaromatherapy.

Side-effects

No known side-effects prior to aromatherapy adminis-tration were reported by these studies, suggesting the mini-mal invasive property of these EOs. In fact, only a fewisolated cases of allergic reactions were documented in theliterature.43 Yet, with its volatility and the skin’s absorbentnature, some EOs do possess the potential to initiate allergicreactions.44 Aromatherapy oil should therefore not be con-sidered as a safe alternative to existing pharmacotherapyuntil rigorous safety trials have been completed. Concerninginhalational aromatherapy, only one incidence of idiosyn-cratic allergic reactions with Anthemis nobilis essential oilswas reported (after inhalation of one drop of smellingstrip).44 This incidence was among two serious cases thatwere indicated by the author after 10 years of teaching inaromatherapy. Thus, although the reviewed studies had notindicated any untoward incidences, the risk still exists, re-quiring precautionary measures to minimize any unwantedconsequences from EOs use.

Outcomes on antiemetic use

The reported outcomes in these reviewed studies havealso highlighted the reduction in the use of analgesic andantiemetic medications. These positive responses are of valuefor extrapolating to gauge the benefits toward less inherentexpenses and potential side-effects related to the pharmacologicinterventions, although the claims were not based on validatedoutcomes measures. Therefore, future trials are recommended,which should include an analysis of medication use as a resultof aromatherapy administration as well as cost effectivenessassessment related to this complementary treatment.

Limitations

Despite the rather captivating findings from this review,there are several limitations that need to be mentioned.First, only five articles were reviewed and more than halfof the studies used small sample sizes. Even though a thor-ough research strategy was employed, it cannot be assuredthat all relevant trials have been located. Second, althoughall the studies have stated that the aromatherapy interven-tion was administered via inhalation, the method and du-ration varied widely, which may directly or indirectlyinfluence the outcomes. Third, due to the restriction im-posed by the search selection criteria, only one study was arandomized controlled trial, while the others were using aquasi-experimental design. No scoring system or qualityassessment for data extraction was adopted for this review,considering the subdued data and the small number ofavailable studies that satisfied the selection criteria. Al-though the excluded studies are not displayed in this review,the inclusion criteria had served as a precise tool in selectingthe articles through which non-peer-reviewed publicationssuch as dissertations and non-English articles were excluded.

Conclusions

In summary, it is concluded that inhaled aromatherapyusing peppermint and ginger EOs may have potential ben-efits in alleviating nausea and vomiting in postoperative andoncology patients. Although the overall outcomes seempromising, methodological weaknesses such as small sample

538 LUA AND ZAKARIA

sizes, quasi-experimental design, imprecise measuring tools,inappropriate placebo, and varied doses or methods of EOsapplication restricted these studies, thus compromising anyconcrete conclusion. Hence, studies of this nature need to befurther replicated and improved before confirmation of theeffectiveness of EOs in treating nausea and vomiting can bestrongly substantiated.

Acknowledgments

The authors would like to sincerely thank Associate Pro-fessor Dr. Nik Mazlan Mamat, Dean, Kulliyyah of AlliedHealth Sciences, International Islamic University Malaysia(IIUM) for his support and guidance.

Disclosure Statement

No competing financial interests exist.

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Address correspondence to:Pei Lin Lua, PhD

Centre for Clinical and Quality of Life StudiesFaculty of Medicine and Health Sciences

Universiti Sultan Zainal AbidinKampus Kota, Jalan Sultan Mahmud

20400 Kuala TerengganuTerengganu 20400

Malaysia

E-mail: peilinlua@unisza.edu.my

540 LUA AND ZAKARIA

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