ContextThe fact that the concept of quality in health care services has come to the fore and that evidence-based practices have become widespread made such concepts as patient satisfaction and comfort important and priority parameters in determining the quality of health services. ObjectivesThe aim of the study is to determine the effects of using lavender oil in intramuscular injection on injection pain, comfort level, blood pressure, pulse rate and respiratory rate. MethodsThe study was designed as a prospective, single-blind randomized controlled trial. The research was conducted in accordance with the CONSORT Checklist guide. In our study, a total of 160 individuals were included in the sample, 80 of whom were control and 80 were intervention. Structured Information Form, Visual Analog Scale and Comfort Scale were used to collect the data of the research. Mann Whitney U, Kruskal Wallis test and Wilcoxon test were used to evaluate the data. ResultsIt was determined that the mean pain scores of the individuals who received intramuscular injection by applying lavender oil were statistically significantly lower than the individuals in the control group. Again, the comfort score averages of the individuals who were applied lavender oil were found to be statistically significantly higher than the control group. It was determined that the blood pressure, pulse rate and respiratory rate before the injection of the individuals in the control group increased statistically significantly according to the post-injection measurements, while the blood pressure, pulse rate and respiratory rate in the lavender oil group decreased significantly after the injection and remained within their normal values. ConclusionAs a result, it was determined that the application of lavender oil in intramuscular injection had a positive and significant effect on the blood pressure, pulse rate and respiratory rate of the individuals on the injection pain and comfort level.