Supplementary Material for: Heterogeneity in the study of peppermint in aromatherapy on cognition and attention: A critical scoping review

Introduction
Aromatherapy has not accrued enough evidence to be integrated into standardized clinical medicine. If high-quality evidence supports the effects of aromatherapy, it will be handled as a parallel option to standardized medical treatment. The aromatherapeutic impact of peppermint (Mentha × piperita L.) essential oil has been researched to a certain extent, such as on pain, anxiety, fatigue, or depression. Considering the rising expenditure on dementia care, the potential effects of peppermint on cognition have become increasingly significant. Therefore, we performed a systematic review of the studies on the impact of peppermint on cognition and attention.
Methods
We focused on human research, and the effects of peppermint scents were required to be inhaled. According to the inclusion criteria, searching from PubMed, Scopus, and Gale Academic OneFile, we identified a total of 115 studies. Finally, eight references were selected for review. The risk of bias was analyzed according to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) criteria.
Results
Each reviewed reference had its own strength in investigating the effects of peppermint scent. However, as most studies have noted, the impact of peppermint should be assessed from multiple perspectives, including psychological, physiological, neurological, and pharmacological factors. The risk of bias was not found to be severe (high risk of bias rate: 35.7 ± 3.4%), our critical review elucidated the heterogeneity of the reviewed studies.
Conclusion
In summary, drawing a definitive conclusion at this stage is premature. Therefore, more carefully designed studies are needed to confirm this hypothesis.