Introduction: Pain is one of the main complications in the immediate postoperative period that can harm the patient and can be managed through pharmacological and non-pharmacological methods. Complementary Integrative Health Practices are non-pharmacological methods that use therapeutic resources based on traditional knowledge to treat symptoms. Among them, aromatherapy stands out, which consists of the use of essential oils through inhalation or topical application for therapeutic purposes and which can be used as a nursing intervention, especially in the context of perioperative care. Objective: To evaluate the effect of aromatherapy on postoperative pain in adult patients in the immediate postoperative period. Method: This is a randomized controlled clinical trial that will be carried out in a teaching hospital. The project was submitted to the Research Ethics Committees of the School of Nursing of the University of Sao Paulo and the University of Sao Paulo Hospital. Adult patients undergoing elective surgical procedures of any surgical specialty under anesthesia of any type will be included. Individuals diagnosed with dementia, cognitive impairment or chronic pain will be excluded; individuals with a history of asthma, allergic bronchitis, chronic obstructive pulmonary disease, contact dermatitis or allergy to cosmetics with lavender fragrance, or hypersensitivity to the compounds used in the intervention; procedure for reoperation for any reason. The intervention will consist of the application of aromatherapy with 2% lavender essential oil through the skin and inhalation by a nurse, associated with usual care, in the immediate postoperative period; the placebo group will only receive the application of grape seed vegetable oil associated with usual care. A numerical verbal scale will be applied to assess pain and vital parameters will be measured upon patient admission, every fifteen minutes in the first hour and every thirty minutes in the second hour or after 15, 30, 45, 60 minutes, 1h30 minutes and 2 hours after applying the intervention, in the post-anesthesia recovery room. Possible associations between variables will be verified using Pearson's Chi-square or Fisher's exact tests. Comparison between means or medians will be made using the Student's t or Mann-Whitney tests, depending on the normality determined according to the Kolmogorov-Smirnov test. The significance level adopted will be 5%.

Inclusion Criteria:

• adult patients undergoing elective surgical procedures of any surgical specialty under anesthesia of any type

Exclusion Criteria:

• individuals diagnosed with dementia, cognitive impairment or chronic pain;
• individuals with a history of asthma, allergic bronchitis, chronic obstructive pulmonary disease, contact dermatitis or allergy to cosmetics with lavender fragrance, or hypersensitivity to the compounds used in the intervention;
• procedure for reoperation for any reason