This randomized controlled trial assessed 80 nurses on the level of sleepiness and alertness during the night shift work following inhalation of rosemary essential oil (EO). Based on previous literature, authors hypothesized rosemary EO could increase alertness given its stimulating effects on the autonomic nervous system (i.e. elevated heart and respiratory rate, raised blood pressure). Eligible nurses included those who had been working a minimum of six rotations of 12-hour shifts each month. Nurses were randomly allocated into the intervention or control group, receiving one drop of either rosemary EO or distilled water in their surgical masks. Researchers assessed the nurses once over the duration of one 12-hour shift, directing nurses to complete an alertness questionnaire before and after wearing the surgical masks for 10-15 minutes. This cycle was repeated every 2 hours. Masks were worn for a short period to prevent adaptation of the olfactory nerves to the scent of rosemary EO. Alertness was assessed after each cycle using the Karolinska Sleep Scale (KSS), a self-report 9-point Likert scale assessing level of sleepiness, as well as the Epworth Sleepiness Survey (ESS), a 3-point self-questionnaire rating the likelihood of dozing off in particular situations. Statistical analysis revealed significantly higher mean difference alertness scores and lower sleepiness scores in the intervention group following inhalation of rosemary EO (P < 0.0001). The results of this study suggest the stimulating scent of rosemary EO can help to improve cognition and reduce drowsiness, thereby reducing the risk for medical errors during shift work. Researchers did not test for long-term use of rosemary essential EO; however, a similar study was referenced in the article suggesting greater cognitive benefits with longer exposure.