What is Rosemary?

Rosemary is a woody evergreen shrub from the Mediterranean, used as a kitchen herb and a folk remedy. The needle-like leaves are used fresh, dried, as tea, as an extract, or distilled into an essential oil.

In European folk use it was linked to memory, alertness, mood, scalp health and digestion. Traditional use tells you people trusted it. It does not prove that it works, and it does not prove that it is safe.

Here is the short verdict. As a food, a tea or a seasoning, rosemary is safe for most adults. As a medicine, the human evidence is thin, and the best studied use is rosemary oil rubbed on the scalp for hair loss.

One hazard matters more than all the claims. The essential oil is strong and must never be swallowed.

How does Rosemary work?

No mechanism for rosemary has been proven in people. What follows comes mostly from lab and animal work.

In cell studies, rosmarinic acid and carnosic acid mop up damaging molecules and appear to damp down signals of inflammation. Whether this happens in a person who drinks rosemary tea is not established.

For hair, the idea is that rosemary oil widens small blood vessels in the scalp and so improves blood flow. This has been shown mainly in animal and laboratory work. One small human trial found hair regrowth, but the reason for it was not pinned down.

For alertness, 1,8-cineole from the smell of rosemary is absorbed into the blood in small human studies. Some of those studies tied higher blood levels to faster, more accurate test scores. The effects were small and the studies were tiny.

In animals, rosemary extract has lowered blood sugar and affected liver enzymes that break down drugs. Human data on both is lacking, which is why some drug cautions below are based on theory, not on proven cases.

What forms does Rosemary come in?

Rosemary is sold in several forms. The kitchen and food ones are:

- Fresh or dried leaf, used in cooking. - Loose-leaf or bagged tea. - Rosemary extract as a food additive, used to stop fats going rancid.

The supplement and oil forms are:

- Capsules and tablets of dried leaf or extract. - Liquid extracts and tinctures. - Essential oil, for scent or for diluted use on skin and scalp.

The essential oil is the most concentrated form by a wide margin. It is for external or scent use only.

Where it comes from:

Rosemary has a long record in European folk practice, going back to Greek and Roman writers and running through medieval and early modern herbals. Students were said to wear sprigs to sharpen the memory.

It also carried a strong symbolic role. Rosemary stood for remembrance at funerals and weddings, and was burned as a strewing herb to freshen sick rooms.

Herbalists of the period gave it for weak digestion, headaches, low spirits and thinning hair. These were the beliefs of their time, written down before controlled testing existed. They describe past practice and are not a recommendation to treat yourself.

What does Rosemary help with?

• Pattern hair loss (thinning at the crown and hairline): This is the best human evidence rosemary has, and it is still limited. One small trial in men compared diluted rosemary oil on the scalp with 2% minoxidil for six months. Both groups showed a modest rise in hair count, with less scalp itch in the rosemary group. It was a single study, with few people and no dummy treatment group. That is not enough to call rosemary a proven hair treatment. It is enough to say the idea is worth asking a doctor about.
• Alertness and memory on tests: Folk use tied rosemary to remembrance, and small modern studies have tested the smell of the oil. Some found slightly faster or more accurate scores on mental tasks after exposure. The effects were small, short-lived and measured in young healthy volunteers. There is no good evidence that rosemary helps dementia, treats memory loss, or protects the brain over time.
• Mild indigestion and wind: European herbal tradition used rosemary tea after heavy meals. Rosemary is accepted in parts of Europe as a traditional herbal remedy for mild digestive complaints, based on long use rather than trial data. Controlled human trials for this use are lacking. If you have ongoing stomach pain, heartburn or reflux, see a doctor instead of self-treating.
• Muscle and joint aches, rubbed on the skin: Diluted rosemary oil has long been used in rubs and bath preparations for stiff muscles. It creates a warm, tingling feeling on the skin, which may be most of what it does. Human trials are few and small. Any relief is likely to be short and mild, and rosemary does not treat the cause of joint disease.
• Stress and low mood, used as a scent: Rosemary is a common aromatherapy oil, and small studies have measured drops in reported stress or in stress hormone levels after sniffing it. The studies are short, small and easily swayed by expectation. Treat this as pleasant rather than proven. It is not a treatment for anxiety or depression.

Which foods are rich in Rosemary?

1. Fresh and dried rosemary leaf
2. Rosemary tea
3. Roast meats, breads and stews seasoned with rosemary
4. Herbes de Provence and similar blends
5. Packaged foods using rosemary extract as a preservative

Practical Tips:

Rosemary eaten as food is safe for nearly everyone, including during pregnancy. Rosemary extract is also added to oils, crisps and meat products to stop fats going rancid. These amounts are small and not a health treatment.

What are the side effects of Rosemary?

• Stomach upset or nausea, mostly with strong extracts
• Heartburn in people prone to reflux
• Skin redness, stinging or rash from the oil
• Allergic skin reaction, including contact dermatitis
• Sun sensitivity in a few people using the oil on skin
• Seizures, vomiting and kidney damage if the essential oil is swallowed

Good to know:

In food and tea amounts, side effects are rare and mild. Most reported problems come from the essential oil or from strong concentrated extracts.

Skin reactions are the most common complaint with the oil. Always dilute it and test a small patch of skin first.

The serious harms are not from cooking with rosemary. They come from swallowing the oil, or from very large amounts of extract. These cases are rare but can be severe.

How much Rosemary should you take?

• Recommended daily: Food amounts of rosemary are not a concern. Labels on rosemary tea often suggest 1 to 2 grams of dried leaf per cup, up to about three cups a day. Capsule labels vary widely, so follow the product label. For the essential oil, no oral dose is given on this page. Swallowing rosemary oil can cause seizures and other serious harm, and there is no safe home amount. On skin, rosemary oil is always diluted in a carrier oil before use. These are the kinds of figures labels carry. They are not advice for you, and a pharmacist or doctor should guide medicinal use.
• Best time of day: Timing does not matter much. Some people avoid rosemary tea late in the evening because the scent feels stimulating, but it has no caffeine. Scalp and skin use can fit any time of day that suits you.
• With or without food: Rosemary tea is often taken after meals in folk use, which is fine. Capsules and extracts may be easier on the stomach with food. If rosemary gives you heartburn or stomach upset, stop taking it.
• Time to effect: Be ready for it to do nothing. Scent effects on alertness, where they happen, come within minutes and fade fast. Digestive comfort from tea, if it comes, is felt in under an hour. Hair change is slow. The one trial measured it at six months. Hair loss has many causes, and rosemary will not fix most of them.
• How long to take it: Rosemary as a food or an occasional tea needs no time limit. Concentrated capsules and extracts have not been tested for long-term safety in people, so a long run is not supported by evidence. In the hair-loss trial, scalp use ran for six months before any change was measured. If you are using rosemary for a health reason and see nothing after a few weeks, stop and ask a clinician.