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19 Health Benefits of Rosemary + Side Effects

Written by Carlos Tello, PhD (Molecular Biology) | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Carlos Tello, PhD (Molecular Biology) | Last updated:

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Rosemary has been used as a medicine since the time of the ancient Greeks. Some traditional practitioners believe that it can improve memory and regrow hair, but the scientific evidence is often scant or contradictory, and it may produce adverse effects in excess. Read on to learn the potential benefits and limitations of rosemary.

What Is Rosemary?

Rosemary (R. officinalis) is a widely used herb that originates from the Mediterranean region. It dates back to the ancient Greeks who hailed the plant for assisting memory and stimulating the brain [1].

The plant contains an essential oil that is needed for survival and known to boost memory [1].

Rosemary is known to have one of the highest antioxidant properties of spices and can combat fungus, bacteria, and cancer [2].

The antioxidant properties of rosemary extracts differ due to [2]:

  • Genetic and growth conditions
  • Geographical origin
  • Climatic conditions
  • Extraction process
  • Quality of original plant
  • Harvesting date
  • Storage and processing

Rosemary can be taken in a wide range of forms including [1, 3, 4, 5, 6]:

  • Powder
  • Tea
  • Extracts
  • Oil

The different forms of rosemary can produce different effects. The extracts especially differ depending on how the rosemary is extracted and what compounds are extracted.

What It’s Made of

Rosemary is made up of a wide variety of oils, phenolic acid derivatives, and phenolic diterpenes including [7]:

  • Oils like 1,8-cineole, α-pinene, camphene, α-terpineol, borneol with antioxidant, antimicrobial, and anticancer effects [7].
  • Phenolic acid derivatives:
    • Rosmarinic acid, found heavily in the leaves, protects the lungs and fights Alzheimer’s [8, 9].
    • Carnosic acid, which protects the brain and has strong antioxidant properties [10, 11].
  • Phenolic diterpenes like carnosol, which has antioxidant effects, protects the liver and improves cognition in Alzheimer’s patients [12, 13, 7].

Rosemary Health Benefits

While rosemary is a safe and popular addition to a healthy diet, rosemary supplements have not been approved by the FDA for medical use. Supplements generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.

1) Memory

In a study of 144 volunteers, aromatherapy with rosemary improved working memory performance, memory quality, and increased alertness. However, memory speed declined compared to controls [14].

In a trial of 28 elderly subjects, low doses (750 mg) of rosemary powder decreased the time taken to remember information. However, at larger doses (>1500 mg) memory speed, attention, and quality of memory declined [1].

20 volunteers scored better and more accurately in simple subtraction tests after being exposed to rosemary aromatherapy. The volunteers’ reaction times were also shorter [15].

Potential Benefits & Early Research

Rosemary is under investigation for a number of other potential benefits, but not enough research has been conducted to know whether it’s safe or effective for any of these purposes.

2) Brain Function

Stress

Rosemary tea reduced symptoms of depression in mice [3].

In a cell study, carnosic acid protected neurons from oxidative stress and overstimulation [11].

A rosemary extract also enhanced the production of NGF [4].

Carnosic acid protected part of the brain (middle cerebral artery) from tissue damage (ischemia/reperfusion injury) and reduced blood clots and brain swelling in rats [11, 16].

Carnosic acid protected against oxidative stress and reduced cell death in rat brains (hippocampus) [17].

Neurodegeneration

Rosemary also prevented beta-amyloid plaques, a key sign of Alzheimer’s disease, from building up in rat brains [18].

Other cognitive disorders, such as dementia and ataxia, are treated by suppressing acetylcholinesterase (AChE). Rosmarinic acid suppressed AchE by 85.8%, even at low doses, suggesting a need for further research on rosemary and degenerative disorders of the brain [9].

Rosemary may have a role in brain health, but many more clinical trials will be needed to fully determine what it is.

3) Skin Health

In a study of 10 healthy subjects, rosemary extracts taken orally protected the skin from UV damage. The extract appeared to become more effective the longer it was taken, with the greatest effect measured at the end of the 12 week trial [5].

More skin cells survived in the volunteers who received rosemary extracts. This protection may have applications in research on aging, cancer, or UV light damage [5, 6].

Rosemary oil is also effective when applied directly to the bacteria (P. acnes) that cause acne. Further studies are required to determine whether rosemary oil could be an effective ingredient for acne-killing skin creams [6].

According to small, early studies, rosemary may improve the skin’s ability to bounce back from stress and damage, but more research is required.

4) Asthma

In a study of 40 asthma patients, rosemary extracts decreased asthma symptoms such as [19]:

  • Wheezing
  • Chest pain
  • Coughing
  • Production of sputum (a mixture of saliva and mucus)

Additionally, rosmarinic acid and rosemary extracts decreased the production of asthma-induced inflammatory cells (eosinophils, neutrophils, and mononuclear cells) in rats [20].

Larger and more robust human trials will be required to determine the possible role of rosemary in the management of asthma.

5) Weight Management

In rats fed high-fat diets, rosemary extracts decreased weight gain by 64% and fat gain by 57% compared to controls [21].

Another study found similar results (69% improvements compared to the controls). While the extract did not decrease food intake, it increased fat loss [22].

These results have yet to be repeated in human trials. Adding rosemary to your diet certainly won’t hurt, but there are better-studied weight loss strategies you can discuss with your doctor.

6) Antioxidants

Rosemary’s active compounds have demonstrated antioxidant activity [2].

In cells, rosemary extracts were better at stopping oxidative damage than commonplace antioxidants such as butylated hydroxytoluene (BHT), Trolox, and ascorbic acid [23, 24].

It is currently unclear how bioavailable rosemary’s antioxidants are or what their effect on a living animal or human might be. However, some researchers have suggested that the antioxidant activity of rosemary could be responsible for some of its health benefits. Further studies will be required to confirm or refute this idea.

7) Antimicrobial Activity

Rosemary has been found to kill microbes when applied directly to cells. It is unclear how rosemary’s antimicrobial activity on contact might be applied to infection in a living animal or human. Future studies will determine whether any of rosemary’s active compounds could be helpful in this way.

Rosemary extracts completely stopped bacterial growth in multiple strains of bacteria (Gram-positive and Gram-negative). The effects were more pronounced for the Gram-positive bacteria [2].

In one study, extracts were able to inhibit 28 of 29 bacterial strains studied [25, 26, 27].

Rosemary has also been found to kill some fungi on direct exposure [2, 27, 28].

Rosemary extracts showed antiviral properties against HIV in a cell study, but only at concentrations that were themselves harmful [29].

Carnosol is a non-toxic compound of rosemary that also has antiviral properties. However, it was not as effective as the rosemary extract [29].

8) Inflammation

Rosemary’s active compounds have not been tested against inflammation in a living animal or human, so these results should be taken with a grain of salt.

At higher doses, rosemary extracts decreased the production of inflammatory molecules (such as IL-1β, COX-1, TNFα, and iNOS) in human cells [30].

It decreases the production of nitric oxide, a product of inflammation [24].

Rosemary essential oil significantly reduced white blood cell (leukocyte) rolling, another process central to the inflammatory response [31].

9) Blood Clots

Cell and mice studies found that rosemary possessed antithrombotic effects, meaning it stopped blood from clotting and restricting blood flow [32].

In a cell study, rosemary reduced the activity of platelets, which are the cells responsible for the clotting of blood [32].

This effect has not been investigated in humans, though it does mean you should be careful with rosemary if you are taking any medication that thins the blood or prevents clotting.

10) Ulcers

Various rosemary extracts decreased ulcers from 44-51.8% in rats. The authors suggested that the antioxidant compounds in rosemary may have brought about this effect; no human trials have yet investigated any link between rosemary and ulcers [33].

11) Gut Health

In animal studies, rosemary extract has been found to:

  • Relieve gas [34].
  • Decrease infections (in rats with colitis/infection of the colon) [35].
  • Discharge bile [34].
    • Bile buildup may reduce the gut’s defense mechanisms [36].
  • Increase bile flow [37].
  • Discharge urine [38]
    • Urine buildup can cause uremia, which is an overflow of waste products in the blood. Urine retention is also common in people with thyroid problems [39].

Researchers are also investigating rosemary’s potential in gut disorders like IBS [35].

These are very early studies which may not apply at all to human health. Future clinical trials are needed to determine rosemary’s effect on the gut.

12) Liver Health

Carnosol (a compound found in rosemary) appeared to prevent liver damage in rats [13].

Carnosol consumption decreased malondialdehyde, a marker of oxidative stress in the liver, by 69%. It also protected the liver tissue from distorting and prevented liver glycogen (energy storage molecules) from depleting [13].

Rosemary extracts decreased plasma glutamic-pyruvic transaminase, a marker of liver injury, by 72% in rats [37].

There are currently no human studies investigating rosemary’s effect on the liver. Future clinical trials will determine whether a benefit exists.

13) Lungs

Giving rabbits rosmarinic acid (found in rosemary) supplements prevented fluid accumulation in the lungs; this has not been studied in humans [8].

14) Menstrual Cramps

In traditional medicine, rosemary has been given to women suffering from painful menstruation (dysmenorrhea). However, this traditional use has not been confirmed in clinical trials [40].

15) Spasms

Rosemary leaves are being investigated for their potential antiepileptic properties [34, 41].

In animals, rosemary has been found to reduce involuntary muscle spasms. Studies of guinea pigs found that rosemary oil reduced spasms in the heart (ileum and atria) [42].

16) Mood

In a study of 144 volunteers, the smell of rosemary brought about feelings of contentment, much more so than those smelling lavender or no smell at all [14].

Mice supplemented with rosemary leaf infusions demonstrated fewer behaviors related to anxiety [3].

Additional human studies will be required to determine whether these effects are clinically significant.

17) Cough

In animal studies, rosemary leaves helped to release mucus and saliva (sputum) and prevent coughs [34, 41].

This is a popular traditional use of rosemary, but it lacks solid clinical research.

18) Hair Growth

In a study (DB-RCT) of 50 patients with androgenetic alopecia (permanent balding), rosemary oil increased hair counts significantly after six months [43].

Hair growth is another popular traditional use of rosemary that lacks solid clinical research. Future trials will clarify its potential role.

19) Arthritis

Some researchers and traditional practitioners have suggested a role for rosemary in arthritis because of its antioxidant activity; arthritis features heavy oxidative damage to the joints and surrounding tissues [34].

This potential use is purely speculative, however; clinical studies will be required.

Cancer Research

Rosemary and its active compounds are currently being investigated for their anti-cancer activity in cell studies. Note that this is very early research; its only purpose is to identify compounds that are worth further study in animal models. The cancer cell types that have been studied include [44, 45, 46]:

  • Ovarian
  • Leukemia
  • Colon
  • Pancreas
  • Breast
  • Prostate
  • Ovaries
  • Cervix
  • Bladder
  • Liver
  • Lung

Carnosic acid is the active compound with the strongest effect on cancer cells so far. Further trials will determine whether it can slow the progression of cancer in a living animal [47, 12, 24].

Both rosmarinic acid and rosemary extracts decreased heterocyclic amines (HCAs), which are cancer-causing molecules found in meats such as beef, chicken, pork, and fish [48].

Side Effects of Rosemary

1) Fertility

Rat’s reproductive organs became smaller after long-term rosemary leaf extract consumption. It also decreased sperm count, mobility, and density. All of these factors negatively affect fertility. Also, pregnant female rats had more fetal loss [49].

2) Skin Irritation & Scalp Itching

In individuals with highly sensitive skin, bath preparations with rosemary oils may cause dermatitis or reddening of the skin (erythema) [50].

In a study (DB-RCT) of 50 permanent balding patients, using rosemary oil to help grow hair increased scalp itching [43].

3) Blood Glucose

Rosemary may raise blood glucose levels. Rabbits with induced diabetes increased glucose levels by 55% in two hours after they were given a large dose of rosemary [51].

4) Convulsions

At high doses, camphor, a compound in rosemary, may cause epilepsy-like convulsions [52].

Limitations

Many of the mentioned studies use high concentrations of rosemary extract to see the intended effects. Therefore, experiencing many of the effects, such as anticancer, might be unlikely with everyday rosemary consumption [53].

Contraindications

Pregnant women are advised not to consume rosemary in excess because of a potential to induce abortion. Breastfeeding women are also advised to use rosemary in moderation [54, 55].

Diabetics and people with high blood sugar are also advised to consume rosemary in moderation as it can raise blood glucose levels [51].

Dosage

A meta-analysis found doses of rosemary extract at 0.1-100 μg/mL to be most effective in fighting cancer. However, an effective dose for human use has not been established due to the wide range of concentrations used in different studies [53].

Overall, the rosemary plant is classified as safe by the FDA and found to have very low toxicity in rats even at high concentrations and extended periods of time [53, 56].

It is recommended to take 4-6 g of rosemary dry leaf/twig supplements daily and 2-4 mL of liquid extracts three times daily [50].

Drug Interactions

1) Chemotherapy Drugs

Rosemary may increase the potency of cisplatin, 5-fluorouracil, and some other chemotherapy drugs. Researchers are investigating whether this effect could be used favorably in a clinical setting, but take caution: increasing the potency of these drugs may also increase their toxicity [44, 57, 58, 10].

You may wish to avoid rosemary entirely if you are currently undergoing chemotherapy. Talk to your doctor to avoid unexpected interactions.

2) Painkillers

Rosemary oil may interact with codeine, acetaminophen (Tylenol), and possibly other painkillers. We do not know what effect this might have on humans; we advise against combining them [40].

As always, talk to your doctor before supplementing to avoid unexpected interactions and adverse effects.

With Citrus Supplements

In a study of 12 volunteers, rosemary extracts with citrus extracts protected the skin against UV damage better than each supplement alone. This is a very small, early study; larger trials will determine the effectiveness of combining rosemary and citrus [5].

About the Author

Carlos Tello

Carlos Tello

PhD (Molecular Biology)
Carlos received his PhD and MS from the Universidad de Sevilla.
Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.

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