Summary of findings 2. Peppermint compared to placebo for treatment of postoperative nausea and vomiting.

Peppermint compared to placebo for treatment of postoperative nausea and vomiting
Patient or population: adults and children having any type of surgical procedure under general anaesthesia, regional anaesthesia or sedation, as hospital inpatients or outpatients, with existing PONV Setting: hospital post‐anaesthesia care unit or same‐day surgery unit in USA Intervention: peppermint Comparison: placebo
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Quality of the evidence (GRADE)	Comments
	Risk with placebo	Risk with peppermint
Nausea severity Assessed with VAS at 5 minutes post‐initial treatment Scale from: 0 to 10 (higher indicates worse nausea)	The mean nausea severity was 2.8 (SD = 10.39)	SMD 0.18 SD lower (0.86 lower to 0.49 higher)	‐	115 (4 RCTs)	⊕⊕⊝⊝ Low1, 2	Risk in placebo group based on control group in Anderson 2004
Nausea duration (nausea‐free at end of treatment) Measured by participant self‐report or medical or nursing observation	See comment		‐	‐	‐	The studies reporting this comparison did not report this outcome.
Use of rescue antiemetics	See comment		‐	‐	‐	The studies reporting this comparison did not report this outcome.
Adverse events (common reactions to aromatherapy include skin rashes, dyspnoea, headache, cardiac arrhythmias, hypotension, hypertension or dizziness)	See comment		‐	‐	‐	The studies reporting this comparison did not report this outcome.
Patient satisfaction with treatment Measured by a validated scale	See comment		‐	‐	‐	The studies reporting this comparison did not report this outcome.
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; PONV: postoperative nausea and vomiting; RCT: randomized controlled trial; SD: standard deviation; SMD: standardized mean difference; VAS: visual analogue scale
GRADE Working Group grades of evidence High quality: we are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low quality: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect Very low quality: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect

¹Risk of bias in included studies due to study designs, downgraded one level.
 ²Significant inconsistency between studies, downgraded one level.