BACKGROUND: Postoperative nausea and vomiting (PONV) is a common, unpleasant phenomenon and current therapies are not always effective for all patients. Aromatherapy has been suggested as an addition to the available treatment strategies. This review was originally published in 2012 and updated in 2017. OBJECTIVES: The main objective was to establish the efficacy and safety of aromatherapy comparable to standard pharmacological treatments for PONV in adults and children. SEARCH METHODS: We searched CENTRAL; MEDLINE; Embase; CINAHL; CAM on PubMed; Informit; LILACS; and ISI Web of Science as well as grey literature sources and the reference lists of retrieved articles up to March 2017. The original search was performed in August 2011. SELECTION CRITERIA: We included all randomized controlled trials (RCTs) and controlled clinical trials (CCTs) where aromatherapy was used to treat PONV. Interventions were all types of aromatherapy compared to placebo or with standard antiemetics. Primary outcomes were severity and duration of PONV. Secondary outcomes were adverse reactions, use of rescue antiemetics and patient satisfaction. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed risk of bias in the included studies and extracted data. For dichotomous outcome variables, we used a random-effects model and calculated risk ratio (RR) with associated 95% confidence interval (95% CI). For continuous outcome variables, we used a random-effects model and calculated standardized mean difference (SMD) with associated 95% CI. We used the GRADE software to compile 'Summary of findings' tables. MAIN RESULTS: We included seven new studies with 663 participants in the 2017 update; five RCTs and two CCTs. These were added to the nine previously included studies (six RCTs and three CCTs with a total of 373 participants) for a total of 16 included studies and 1036 participants in this updated review. The mean age and range data for all participants were not reported for all studies. We identified two registered trials that met the inclusion criteria for this review; however there are no results for these studies yet.Overall, the GRADE assessment of evidence quality ranged from moderate to very low. The method of randomization in 11 of the 12 included RCTs was explicitly stated and adequate. Incomplete or methodologically diverse reporting of data affected the completeness of the analysis. Data on additional aromatherapies were added in the 2017 update (blended aromatherapy products, and peppermint products). Heterogeneity of outcome measures and time points between studies affected the completeness of the analysis.In the summary of the findings of six studies, we did not find aromatherapy to be effective in reducing nausea severity in comparison to placebo (SMD -0.22, 95% CI -0.63 to 0.18, P value = 0.28, 241 participants, level of evidence: low). Those participants receiving aromatherapy were no more likely to be free of nausea at the end of the treatment period than those receiving placebo (RR 3.25, 95% CI 0.31 to 34.33, P value = 0.33, 4 trials, 193 participants, evidence level: very low), however they were less likely to require rescue antiemetics (RR 0.60, 95% CI 0.37 to 0.97, P value = 0.04, 7 trials, 609 participants, evidence level: low). There were no data reported on adverse events or patient satisfaction for this comparison.A specific comparison of peppermint aromatherapy to placebo did not show evidence of an effect on nausea severity at five minutes post-treatment in the pooled results (SMD -0.18, 95% CI -0.86 to 0.49, P value = 0.59, 4 trials, 115 participants, evidence level: low). There were no data reported on nausea duration, use of rescue antiemetics, adverse events or patient satisfaction for this comparison.When we pooled studies comparing isopropyl alcohol to standard antiemetic treatment in a GRADE summary of findings, in terms of nausea duration, there was a significant effect on the time in minutes to a 50% reduction in nausea scores (SMD -1.10, 95% CI -1.43 to -0.78, P value < 0.00001, 3 trials, 176 participants, evidence level: moderate). Fewer participants who received isopropyl alcohol required rescue antiemetics (RR 0.67, 95% CI 0.46 to 0.98, P value = 0.04, 215 participants, 4 trials, evidence level: moderate). Two studies with 172 participants measured patient satisfaction; there were high levels of satisfaction across both aromatherapy and standard treatment groups and no differences found (evidence level: low). There were no data reported on nausea severity or adverse events for this comparison.There was no difference in effectiveness between isopropyl alcohol vapour inhalation and placebo for reducing the proportion of participants requiring rescue antiemetics (RR 0.39, 95% CI 0.12 to 1.24, P value = 0.11, 291 participants, 4 trials, evidence level: very low). There were no data reported on nausea severity, nausea duration, adverse events or patient satisfaction for this comparison. AUTHORS' CONCLUSIONS: Overall, for nausea severity at the end of treatment, aromatherapy may have similar effectiveness to placebo and similar numbers of participants were nausea-free. However, this finding is based on low-quality evidence and therefore very uncertain. Low-quality evidence also suggests that participants who received aromatherapy may need fewer antiemetic medications, but again, this is uncertain. Participants receiving either aromatherapy or antiemetic medications may report similar levels of satisfaction with their treatment, according to low-quality evidence.