Benefits
Memory and mental performance
In a one-month trial in 68 students, 500 mg rosemary twice daily improved self-rated memory versus placebo. In older adults, a single 750 mg dose of dried leaf sped up memory tasks, but a 6 g dose slowed them. A rosemary-water drink gave small gains on some tests, while a single 1.7 g capsule did not improve attention in young adults. All studies were small.
Anxiety scores in adults under daily stress
In a maker-funded crossover trial in 38 adults with daily stress, 4 weeks of an extract giving 5 mg rosmarinic acid and 8 mg diterpenes daily lowered trait anxiety versus placebo, and one dose lowered anxiety after a stressful task. Cortisol and ratings of stress and fatigue did not change. The student trial also found lower anxiety scores.
Mood and anxiety questionnaire scores
In an 8-week placebo-controlled trial in patients with major depressive disorder, rosemary capsules twice daily given as an add-on to their treatment lowered depression and anxiety questionnaire scores more than placebo. A small subgroup of Japanese working men with higher mood-disturbance scores also improved on a mood scale. Depression needs medical care, and rosemary is not a substitute for it.
Sleep quality scores in students
In the one-month student trial, 500 mg rosemary twice daily improved the overall Pittsburgh sleep quality score versus placebo, but the time taken to fall asleep and total sleep time did not change. In a small subgroup of working men, daytime sleepiness eased only compared with their own starting scores. Sleep was a secondary, self-rated outcome.
Cognitive screening scores in a two-month patient trial
In a two-month triple-blind trial in 77 adults with COPD, 500 mg rosemary extract capsules twice daily raised scores on a cognitive screening test, and after adjustment for sleep apnea the gain was larger than with placebo. One of two daily-living scales improved only in that adjusted model. This is a single patient trial using a screening test.
Alertness and memory during rosemary aroma (inhaled, not oral)
Several studies had people smell rosemary essential oil rather than swallow it. In 144 adults, the aroma improved overall memory quality but slowed memory speed; in 20 adults, higher blood levels of the aroma compound 1,8-cineole tracked better task scores; and shift-working nurses rated themselves less sleepy. These results do not show that oral supplements work the same way.
Mechanism of action
Carnosic acid switches on antioxidant defences
In cell and rodent studies, carnosic acid activated the Keap1/Nrf2 pathway, the cell's own antioxidant switch, reached the brain and raised glutathione levels in animals, and protected nerve cells from oxidative stress. Whether ordinary supplement doses do this in people has not been measured.
Aroma compounds reach the blood
After people sat in a room with rosemary oil aroma, the volatile compound 1,8-cineole was measurable in their blood, and higher levels went with better task scores. Researchers have proposed effects on acetylcholine signalling, but this was not tested directly in people.
Extracts differ in what they contain
A hot-water rosemary extract used in one Japanese trial supplied rosmarinic acid, with no carnosic acid or 1,8-cineole detected, while another trial's extract was standardized to both rosmarinic acid and carnosic acid plus carnosol. Results from one type of extract may not apply to another.
Clinical trials
Double-blind, randomized, placebo-controlled trial of 500 mg rosemary twice daily for one month, with memory, anxiety, depression and sleep measured by questionnaires (Nematolahi et al. 2018, Complement Ther Clin Pract).
68 university students in Iran.
Compared with placebo, the rosemary group scored better on prospective and retrospective memory questionnaires, anxiety and depression (HADS) and overall sleep quality (PSQI). Sleep latency and sleep duration did not change significantly. All outcomes were self-rated, the trial was short and single-center, and it has not been repeated in another student group.
Randomized, double-blind, placebo-controlled crossover (4 weeks per phase, 4-week washout) of a rosemary extract giving 5 mg rosmarinic acid plus 8 mg carnosic acid and carnosol daily, with a separate 4-week open-label safety study at 5 times that dose (Kuwata et al. 2025, J Clin Biochem Nutr).
40 healthy Japanese adults aged 20 to 60 with daily stress (38 analyzed); 22 healthy adults in the safety study.
Trait anxiety (STAI) and the heart-rate-variability LF/HF ratio fell more after 4 weeks of extract than placebo, and a single dose lowered state anxiety after a stressful mental task. State anxiety after 4 weeks, ratings of fatigue, stress and relaxation, and salivary cortisol did not differ from placebo. All authors work for the extract maker (NIPPN), which funded both studies.
Randomized, double-blind, placebo-controlled trial of one rosemary capsule twice daily for 8 weeks as an add-on (adjunctive) treatment (Azizi et al. 2022, Complement Ther Clin Pract).
Patients with diagnosed major depressive disorder in Iran.
At 8 weeks, anxiety (HADS anxiety subscale) and depression (Beck Depression Inventory II) scores were lower in the rosemary group than the placebo group; the authors also reported better memory. The abstract does not give the number of patients or the capsule dose, and the trial comes from the same research group as the student study. This is research on a medically treated condition, not a substitute for care.
Randomized, placebo-controlled, double-blind crossover of four single doses of dried rosemary leaf powder (750 mg up to 6,000 mg), with a 7-day washout between visits (Pengelly et al. 2012, J Med Food).
28 older adults, mean age 75.
The 750 mg dose improved speed of memory compared with placebo, but the 6,000 mg dose impaired it, and other cognitive measures showed less consistent impairing effects. The study tested single doses only, so it says nothing about daily use.
Triple-blind randomized trial of 500 mg rosemary hydroalcoholic extract capsules twice daily versus corn-powder capsules for two months (Momeni Safarabadi et al. 2024, Explore (NY)).
77 patients with chronic obstructive pulmonary disease aged 40 to 80 in Iran.
Total cognitive screening scores (MoCA-B) rose within the rosemary group. Unadjusted, the groups did not differ on the two daily-living scales. In a model adjusted for obstructive sleep apnea, gains in cognition and in the Lawton IADL scale were larger than with placebo, while the lung-specific scale (LCADL) still did not differ. A patient trial using a screening test, not a study of healthy people.