Rosemary extract

What it is

Rosemary extract is made from the leaves of the rosemary plant. Its main antioxidant components are the phenolic diterpenes carnosol and carnosic acid, and the leaf also contains rosmarinic acid and a volatile oil rich in 1,8-cineole and camphor. Extracts of rosemary are used as a food antioxidant at 30-1000 mg/kg, expressed as carnosol plus carnosic acid.

What the research says

Rosemary is claimed to help memory, inflammation and antioxidant status. Human trials are few, small and short. In a crossover trial in 28 older adults, the lowest dose (750 mg) improved speed of memory while the highest dose (6,000 mg) impaired it. A 12-week trial in 72 rheumatoid arthritis patients reported improved disease scores but no difference in morning stiffness or TNF-alpha, and a one-month trial in 50 young adults found no change in lipid peroxidation. Contact dermatitis from rosemary, often attributed to carnosol, is documented in case reports.

Evidence grade: Limited evidence.

What goes wrong

In the same trial a single 6,000 mg dose significantly impaired speed of memory. (Source 1)

• Randomized trial, Low certainty.
• Size: 28 older adults.
• Who: older adults, mean age 75.
• How long: acute: single doses, tested over hours.
• Result: significant impairment at 6,000 mg (P < .01 as reported in the abstract)
• Funding: industry-funded (McCormick Science Institute)

the highest dose (6,000 mg) had a significant impairing effect

Case reports document allergic contact dermatitis from rosemary, including a worker who developed severe dermatitis after rosemary extract was introduced as a preservative; the diterpene carnosol is implicated. (Source 2)

• Case series, Very low certainty.
• Size: individual case reports reviewed.
• Who: workers and consumers exposed to rosemary leaves, extracts or plasters.
• How long: hours to weeks after exposure.
• Result: vesicular and exudative dermatitis; no incidence rate.
• Funding: not stated.

The diterpene carnosol, a chemical constituent of this plant, has been imputed as a common cause for this reaction.

In patch testing reported by the Cosmetic Ingredient Review panel, rosemary leaves produced irritation reactions in 44 of 234 patients with contact dermatitis or eczema. (Source 3)

• Case series, Low certainty.
• Size: 234 patients.
• Who: patients with contact dermatitis or eczema.
• How long: patch test.
• Result: 44/234 (about 19%) scored as irritation (+/-, +, or ++); these are irritation reactions, not confirmed allergy, and the panel reports no allergy rate.
• Funding: industry-funded safety panel (Cosmetic Ingredient Review)

Rosmarinus officinalis (rosemary) leaves produced irritation (scores of +/-, +, or ++) in 44/234 patients with contact dermatitis or eczema.

Cosmetic Ingredient Review Expert Panel position (2014): rosemary-derived ingredients are safe in cosmetics when formulated to be non-sensitising. (Source 3)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: cosmetic users.
• How long: not applicable.
• Result: safe only when formulated to be non-sensitizing.
• Funding: industry-funded panel.

concluded these ingredients are safe as used in cosmetics when formulated to be non-sensitizing

What the evidence supports

In a double-blind crossover trial in 28 older adults, a single 750 mg dose of rosemary powder improved speed of memory versus placebo. (Source 1)

• Randomized trial, Low certainty.
• Size: 28 older adults.
• Who: older adults, mean age 75.
• How long: acute: single doses, with cognitive testing in the hours after each dose.
• Result: statistically significant benefit on speed of memory at 750 mg (P = .01 as reported in the abstract)
• Funding: industry-funded (McCormick Science Institute sponsored and supplied the rosemary)

the lowest dose (750 mg) of rosemary had a statistically significant beneficial effect compared with placebo

In a 12-week double-blind RCT, 4 g/day rosemary leaf powder alongside standard medication improved DAS-28, joint counts, CRP and ESR in rheumatoid arthritis. (Source 4)

• Randomized trial, Low certainty.
• Size: 72 patients.
• Who: adults with rheumatoid arthritis on standard medication.
• How long: 12 weeks.
• Result: significant changes in DAS-28, TJC, SJC, VAS, CRP, ESR, TAC, MDA; numbers not recorded.
• Funding: independent (Iran University of Medical Sciences grant 21771)

72 patients with rheumatoid arthritis were randomly assigned to two groups

What the evidence does not support

In the same RA trial, rosemary made no significant difference to morning stiffness, patient global assessment or TNF-alpha. (Source 4)

• Randomized trial, Low certainty.
• Size: 72 patients.
• Who: adults with rheumatoid arthritis.
• How long: 12 weeks.
• Result: no significant between-group difference.
• Funding: independent (Iran University of Medical Sciences)

no significant difference in morning stiffness

In a one-month double-blind RCT in 50 healthy young adults, 1,000 mg/day rosemary lowered acetylcholinesterase activity but did not change lipid peroxidation. (Source 5)

• Randomized trial, Low certainty.
• Size: 50 healthy participants (25 per group)
• Who: healthy adults aged 21-25.
• How long: 30 days.
• Result: no significant change in lipid peroxidation (p>0.05); AChE activity decreased.
• Funding: not stated.

no significant changes were observed in lipid peroxidation (p value>0.05)

Where the research disagrees

Whether more rosemary helps memory

• Pengelly et al. 2012 (low dose), crossover RCT, n=28, industry-sponsored: "the lowest dose (750 mg) of rosemary had a statistically significant beneficial effect compared with placebo" (Source 1)
• Pengelly et al. 2012 (high dose), same crossover RCT: "the highest dose (6,000 mg) had a significant impairing effect" (Source 1)

How much

• Reference intake: No recommended intake exists; rosemary extract is not a nutrient. It is regulated as a food antioxidant by maximum use levels. (Source 3)
• Upper limit: No tolerable upper intake level was found in the sources we could reach. Food additive use levels of 30-1000 mg/kg (as carnosol plus carnosic acid) are cited. JECFA/EFSA ADI documents could not be fetched and were not verified. (Source 3)
• Studied: Single doses of 750 mg to 6,000 mg dried rosemary powder in older adults (crossover). (Source 1)
• Studied: 4 g/day rosemary leaf powder versus 4 g/day starch placebo for 12 weeks in rheumatoid arthritis. (Source 4)
• Studied: 500 mg rosemary powder twice daily for one month in healthy young adults. (Source 5)

A common belief, and what the research shows

The belief: If a little rosemary helps memory, more is better.

What the research shows: In the one dose-ranging trial, "the highest dose (6,000 mg) had a significant impairing effect" while only the lowest dose helped.

Questions and answers

What is it?

Rosemary extract comes from the leaves of the rosemary herb. Its main active antioxidant compounds are carnosol and carnosic acid. (Source 3)

What does it do in the body?

Rosemary compounds act as antioxidants. In people, one small industry-sponsored trial found a low culinary-level dose sped up memory in older adults, but the evidence is thin and a high dose impaired memory. (Source 1)

Is it good or bad for you?

At culinary amounts rosemary is widely eaten. Trial benefits are small and preliminary; a high 6,000 mg dose impaired memory in one trial, and skin contact can cause allergic dermatitis in some people. (Source 1)

How do you get more of it?

People take in rosemary compounds from the herb in cooking, from foods preserved with rosemary extract, and from supplements. Trials used dried leaf powder capsules. (Source 3)

If it is harmful, what reduces it?

Rosemary is not something the body needs to clear. In reported contact allergy cases, the dermatitis improved once the rosemary product was withdrawn. (Source 2)

Why might someone be low in it or missing it?

Does not apply. Rosemary is not a nutrient, so no one is deficient in it; intake simply depends on diet. (Source 3)

Which whole foods contain it or feed it?

The rosemary leaf is the main food source; the key compounds are found at lower levels in flowers, stems and roots. (Source 3)

What happens if you do not have it?

Nothing known. No harm from not eating rosemary is described in the literature we searched. (Source 3)

We searched: Web searches for rosemary systematic reviews, trials and safety assessments (CIR 2014, Pengelly 2012, Bayat 2025); none address absence.

How can you test for it?

There is no routine test for rosemary intake. Suspected rosemary skin allergy is assessed by patch testing; in one series rosemary leaves produced irritation in 44 of 234 patients with dermatitis or eczema, and those were irritation reactions rather than confirmed allergy, so patch results need careful reading. (Source 3)

References

1. Journal of Medicinal Food. Short-Term Study on the Effects of Rosemary on Cognitive Function in an Elderly Population. 2012. PMID 21877951, DOI 10.1089/jmf.2011.0005. Read the source
2. Allergologia et Immunopathologia. Rosmarinus officinalis L. as cause of contact dermatitis. 2014. DOI 10.1016/j.aller.2013.04.006. Read the source
3. Cosmetic Ingredient Review Expert Panel. Safety Assessment of Rosmarinus Officinalis (Rosemary)-Derived Ingredients as Used in Cosmetics. 2014. Read the source
4. Journal of Functional Foods. The effect of rosemary leaf powder on disease symptoms, inflammatory and oxidative markers in patients with rheumatoid arthritis: A double-blinded randomized controlled clinical trial. 2025. DOI 10.1016/j.jff.2025.106878. Read the source
5. Advances in Integrative Medicine. Antioxidant and anticholinesterase effects of rosemary (Salvia rosmarinus) extract: A double-blind randomized controlled trial. 2022. DOI 10.1016/j.aimed.2021.03.002. Read the source