Olive Leaf

Olea europaea L. was named by Linnaeus in Species Plantarum in 1753 and is the accepted name in Kew’s Plants of the World Online (POWO), which places it in the olive family, Oleaceae. Liccardi and colleagues (International Archives of Allergy and Immunology 1996) list its relatives as ash (Fraxinus), privet (Ligustrum), and Phillyrea, along with forsythia, jasmine, and lilac (Syringa). POWO gives a native range from Africa and the Mediterranean to south-central China and describes a shrub or tree of the subtropical biome used for food, fuel, animal fodder, and medicine. It accepts seven subspecies: europaea, africana, cerasiformis, cuspidata, guanchica, laperrinei, and maroccana. A note in POWO drawn from the Flora of Somalia explains that subsp. europaea, with larger edible fruits and a thick fleshy pulp, is the cultivated olive, while laperrinei is the wild olive of the Saharan mountains and cerasiformis that of the Macaronesian islands; subsp. cuspidata ranges from the Arabian Peninsula to Yunnan in China. EMA’s assessment report adds that the cultivated tree is grown in similar climates far beyond the Mediterranean, including the Americas.

EMA’s assessment report describes an evergreen tree about 6 to 9 m tall with narrow, opposite, lance-shaped leaves that have smooth edges and pointed tips, gray-green above and paler beneath, where fine white scale-like hairs give the leaf its silvery sheen. The European Pharmacopoeia defines the medicinal leaf as simple, thick, and leathery, 30 to 50 mm long and 10 to 15 mm wide, with a small sharp point at the tip, smooth and shiny above and paler and hairy below. Under the microscope, the powder shows many shield-shaped hairs and long, thick-walled stone cells, which help analysts confirm its identity. The small white flowers grow in branched clusters, and the fruit is a drupe, a single-stoned fruit like a cherry. Olive pollen travels on the wind; Liccardi and colleagues note that the olive pollen season in the Mediterranean runs from May to the end of June. Leaves for medicine are harvested year-round from cultivated trees and dried in the shade, and they taste bitter.

The leaf’s chemistry centers on secoiridoids, bitter compounds typical of the olive family. The main one is oleuropein (C25H32O13), discovered in 1908 by Bourquelot and Vintilesco and shown by Panizzi and colleagues in 1960 to be a sugar-bound ester of elenolic acid and hydroxytyrosol. EMA’s assessment report cites 60 to 90 mg of oleuropein per gram of dried leaf, and the European Pharmacopoeia requires at least 5%. Relatives include ligstroside, which carries tyrosol in place of hydroxytyrosol, oleuroside, and oleoside derivatives. The leaf also contains flavonoids (luteolin, apigenin, kaempferol, and chrysoeriol), triterpenes such as oleanolic and maslinic acid, phenolic acids including caffeic and ferulic acid, and coumarins. EMA notes that oleuropein is plentiful in the leaves but present only in low amounts in olive oil, where it contributes bitterness and pungency, and that it is the bitter material removed when table olives are cured. As olives ripen, enzymes break oleuropein down, so its level in the fruit falls.

The olive is one of the oldest crops of the Mediterranean. Besnard and colleagues (Proceedings of the Royal Society B 2013) profiled the plastid DNA of 1,263 wild olives and 534 cultivated ones and found three long-term refuges for wild trees, in the Near East including Cyprus, the Aegean, and around the Strait of Gibraltar. Their data place the first domestication in the northern Levant, followed by spread across the Mediterranean basin alongside the expansion of its civilizations. The leaves entered folk medicine across the region. EMA’s assessment report, drawing largely on a 2007 compilation by Khan and colleagues, records leaf infusions taken for high blood pressure in Spain, Greece, Italy, Bulgaria, Madeira, and Tunisia; for diabetes in the Canary Islands, Spain, Mexico, and the former Yugoslavia; for stomach and intestinal complaints in Morocco; and for diarrhea and respiratory and urinary infections in Argentina. Italians applied the fresh leaf to wounds, and in Kenya the twigs of the African subspecies serve as chewing sticks.

The leaf’s first formal medical role was as a fever remedy. EMA’s assessment report recounts that Spanish physicians in the early nineteenth century sometimes prescribed olive leaves as a febrifuge, that French medical officers (officiers de santé) used them for intermittent fevers during the war in Spain of 1808 to 1813, and that the practice became known in England for Britons returning sick from the tropical colonies. In 1854 the Pharmaceutical Journal published a report by Daniel Hanbury describing an olive leaf tincture for fever and malaria, and the bitter principle he suspected was later isolated and named oleuropein. Laboratory interest grew in the twentieth century: EMA records Italian work in the 1960s reporting that oleuropein lowered blood pressure in animals, and Bulgarian studies by Petkov and Manolov (1972) describing effects on blood pressure, coronary blood flow, and heart rhythm in animals. These animal findings, not human trials, shaped the leaf’s modern reputation as a heart herb.

Olive leaf became a licensed medicine in parts of Europe. EMA lists powdered leaf capsules sold in France since 1980 “to promote urinary and digestive elimination functions,” leaf products in Spain since 1986 for water excretion and cardiovascular support, and German ethanol extracts marketed from 1976 until 2011 “to support the cardiovascular system,” sometimes combined with rauwolfia, veratrum, or mistletoe. Germany’s Commission E nonetheless issued a negative monograph. When EMA’s herbal committee wrote its monograph, adopted in 2017, it accepted only the water-retention use, excluding the German extracts because a heart indication is unsuitable for self-medication. A 2025 periodic review screened 238 new references and found none that justified a change. Meanwhile, olive leaf extract became a mass-market supplement. In the New Zealand Medical Journal in 2016, the toxicologist Ian Shaw listed claims made for it, including anti-aging, immune stimulation, blood pressure and blood sugar control, and use as an antibiotic, and judged the supporting evidence scant and sometimes contradictory.

EMA concludes that olive leaf’s mechanism of action “cannot be considered clarified” and that the body probably absorbs its phenolic compounds poorly and variably. Oleuropein can be split into hydroxytyrosol, elenolic acid, and glucose, and hydroxytyrosol is the form that mostly reaches the blood. De Bock and colleagues (Molecular Nutrition and Food Research 2013) gave single doses of a commercial extract to nine volunteers and found that the main compounds in blood and urine were hydroxytyrosol bound to sulfate or glucuronic acid, the body’s usual way of preparing compounds for excretion. Liquid extract produced higher oleuropein peaks than capsules, men absorbed more hydroxytyrosol than women, all the conjugated hydroxytyrosol was cleared in urine within eight hours, and individuals varied widely. That variation is one possible reason trial results differ.

Most of the blood pressure mechanism comes from animals and isolated tissues. In rats given the drug L-NAME, which raises blood pressure by blocking nitric oxide, Khayyal and colleagues (2002, cited by EMA) found that the extract later tested by Susalit prevented the rise in a dose-dependent way, with the best effect at 100 mg per kg. Leaf extracts relaxed isolated rat arteries whether or not their inner lining was intact (Zarzuelo and colleagues 1991), an extract blocked L-type calcium channels in rat heart cells, as some blood pressure drugs do (Scheffler and colleagues 2008), and a related secoiridoid, oleacein, inhibited angiotensin-converting enzyme (ACE), the target of drugs such as captopril, in laboratory tests (Hansen and colleagues 1996). In people, Lockyer and colleagues (British Journal of Nutrition 2015) gave 18 healthy volunteers a single dose providing 51 mg of oleuropein and 10 mg of hydroxytyrosol; over the next hours, a measure of arterial stiffness fell compared with a control, and their blood produced less of the inflammatory messenger interleukin-8 when stimulated in the laboratory. That is a short-term signal, not proof of lasting benefit.

For blood sugar, Wainstein and colleagues (Journal of Medical Food 2012) found that an olive leaf extract reduced starch digestion and absorption in segments of rat intestine, and MSKCC summarizes older animal work suggesting that leaf extracts boost glucose-triggered insulin release and glucose uptake into tissues, with stronger effects from leaves picked in winter. EMA notes that such effects appeared only at high doses in animals. Laboratory studies cited by MSKCC show that olive leaf extracts inhibit bacteria such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae, along with Candida yeasts and skin fungi, in the test tube. Concentrations in a dish say little about what a capsule does inside the body, where oleuropein is quickly broken down and cleared. Diuretic effects have been seen in rats given leaf extracts, but there is no modern human study explaining how, or whether, olive leaf increases urine flow.

High blood pressure is the use with the most human research, and nearly all of it tests branded extracts. Susalit and colleagues (Phytomedicine 2011) enrolled 232 Indonesian adults with stage 1 hypertension, put them on diet alone for four weeks, then randomized those still hypertensive to 500 mg of the extract EFLA 943 twice daily or captopril 12.5 to 25 mg twice daily for eight weeks. Among the 148 analyzed, systolic pressure fell by 11.5 mmHg with the extract and 13.7 mmHg with captopril, a difference that was not statistically significant, and triglycerides fell only with the extract. Without a placebo group, the trial cannot show how much of the fall was due to the extract; it was supported by Frutarom, which made the extract, and Dexa Medica, which supplied both study products. In an earlier open study led by a Frutarom scientist, Perrinjaquet-Moccetti and colleagues (Phytotherapy Research 2008) gave the same extract to 20 pairs of identical twins with borderline readings; average pressure fell from 137/80 to 126/76 mmHg on 1,000 mg a day but not on 500 mg. Lockyer and colleagues (European Journal of Nutrition 2017) ran a double-blind crossover trial in 60 men with prehypertension: six weeks of an extract providing 136 mg of oleuropein a day lowered 24-hour systolic pressure by 3.3 mmHg and diastolic by 2.4 mmHg compared with a control, with small falls in LDL cholesterol and triglycerides. Half the funding came from Comvita, the extract’s maker.

Not every trial agrees, and the overall picture is a modest effect. Stevens and colleagues (European Journal of Nutrition 2021) gave 500 mg of a water-based extract or placebo for eight weeks to 77 overweight adults with mildly raised cholesterol and found no difference in blood pressure, cholesterol, blood sugar, or liver tests; the lead author worked for BioActor, a Dutch company. Wong and colleagues (Nutrients 2014), funded by HealthWorld Ltd., which supplied the products, found no effect on 24-hour pressure in 37 adults from a combination of olive leaf, green coffee bean, and beetroot extracts. The largest trial, by Lamti and colleagues (Journal of Hypertension 2025), gave an extract or placebo for 12 weeks to 621 Tunisians being treated for hypertension; 24-hour systolic pressure fell by about 6.4 mmHg with the extract and 1.5 mmHg with placebo, and one author was affiliated with a Tunisian company, Belpharma Laboratories. Razmpoosh and colleagues (Diabetology and Metabolic Syndrome 2022) pooled 12 trials with 819 participants and found systolic pressure about 3.9 mmHg lower, and Mansouri and colleagues (Nutrition, Metabolism and Cardiovascular Diseases 2026) found lower systolic and diastolic pressure and better blood lipids across olive leaf trials, with certainty ranging from very low to high. Verdict: a small blood pressure–lowering effect is plausible, but trials are short, mostly sponsored, and use different extracts, none has measured heart attacks or strokes, and EMA judged the data insufficient for a well-established use.

Blood sugar results are inconsistent. De Bock and colleagues (PLoS One 2013) gave 46 overweight middle-aged men in New Zealand capsules supplying 51.1 mg of oleuropein and 9.7 mg of hydroxytyrosol a day, or placebo, for 12 weeks each in a crossover design; insulin sensitivity improved by 15% and the insulin-secreting capacity of the pancreas by 28%, though blood pressure, cholesterol, and body composition did not change. Comvita supplied the extract and placebo and half-funded the grant. When Comvita asked EFSA to approve a claim that its extract increases glucose tolerance, EFSA (2014) concluded that the result had not been replicated and the evidence was insufficient. Wainstein and colleagues reported lower HbA1c (a three-month average of blood sugar) and fasting insulin after 14 weeks of 500 mg a day in 79 adults with type 2 diabetes, but a 24-week Australian pilot trial in 31 adults with type 2 diabetes found no difference in HbA1c (Leach and Breakspear, Complementary Therapies in Clinical Practice 2025), and a product combining fenugreek, olive leaf, and bergamot did not improve HbA1c over six months in 100 Greek adults with prediabetes (Florentin and colleagues 2019). Meta-analyses by Razmpoosh and colleagues and by Mansouri and colleagues found no meaningful effect on blood sugar markers. Verdict: not a diabetes treatment.

Colds, flu, and “immune support” are popular marketing claims with little human evidence. EMA’s assessment report quotes a 2005 reference noting that olive leaf is commonly used for colds and flu, yeast infections, and viral infections such as shingles and herpes, and laboratory studies summarized by MSKCC show leaf extracts inhibiting bacteria, yeasts, and fungi in a dish. The one trial on everyday respiratory illness is small: Somerville and colleagues (Nutrients 2019), funded by a University of Auckland seed grant, randomized 32 high school athletes to a daily tablet equivalent to 20 g of leaf (100 mg of oleuropein) or placebo for nine weeks. The number who fell ill did not differ, but the extract group had 28% fewer sick days. In 150 hospitalized COVID-19 patients in Iran, Ahmadpour and colleagues (Explore 2023) reported better vital signs and inflammatory markers after five days of extract than placebo, a single trial that has not been repeated. EFSA rejected olive polyphenol claims about upper respiratory tract health and body defenses as too vague to assess. On the skin, an Iranian trial in 66 people found that a 2% olive leaf cream eased cold sores faster than 5% acyclovir cream (Toulabi and colleagues, Explore 2022), a result that also needs confirming. Verdict: there is no reliable evidence that olive leaf prevents or treats colds or flu.

Water retention is the only use EMA accepts, and it rests on tradition. EMA cites an old controlled study by Capretti and Bonaconza (1949) in which an olive leaf infusion or decoction raised daily urine output by 100 to 145 ml without changing blood sodium, potassium, or chloride, but notes that its details are insufficient. Health Canada likewise allows olive leaf to be labeled as used in herbal medicine as a diuretic, for occasional use only, and as a source of antioxidants; neither regulator permits a blood pressure claim. Swelling of the ankles, legs, or face can be a sign of heart, kidney, or liver disease, which is why EMA requires a doctor to rule out serious causes first. Olive leaf is also sold for cholesterol, where small falls appeared in some trials and not in others, and for cancer, which MSKCC says olive leaf extract has not been shown to prevent or treat in humans. Anyone interested in herbs with blood pressure research may also want to compare the evidence for hibiscus, garlic, and hawthorn.

EMA’s monograph covers whole, cut, and powdered dried leaves for adults, used for two to four weeks. For a decoction, 10 g of fresh or 5 g of dried leaves are simmered in 150 ml of water until 100 ml remains, taken morning and evening. As an infusion, the single dose is 6 to 10 g of dried leaf up to three times a day, a daily total of 6 to 30 g. Powdered leaf is taken as 275 mg three to five times a day or 210 to 400 mg three times a day, a daily total of 630 to 1,375 mg. EMA advises seeing a doctor if symptoms last more than a week or get worse. Health Canada’s monograph allows similar teas, limits extracts to the equivalent of 3.5 g of dried leaf a day, caps standardized extracts at 20.8% oleuropein, and restricts diuretic use to occasional use. The leaf is strongly bitter, so teas are an acquired taste.

The extracts used in trials are not interchangeable. EFLA 943, tested by Susalit and colleagues at 500 mg twice daily, is made with 80% ethanol from 3 to 7 parts of leaf per part of extract, and the batch in that trial contained 19.9% oleuropein. Comvita’s extract in the Lockyer trial supplied 136 mg of oleuropein and 6 mg of hydroxytyrosol a day, while the same company’s capsules in the de Bock trial supplied 51.1 mg and 9.7 mg. The water-based extract in the Stevens trial, given at 500 mg a day, provided 83.5 mg of oleuropein, according to EMA’s 2025 review, and the tablet in the Somerville trial was equivalent to 20 g of leaf. Daily oleuropein doses in trials therefore range several-fold, and benefits seen with one product cannot be assumed for another. De Bock and colleagues also found that a liquid extract produced higher blood levels of oleuropein than capsules. Labels that state the plant part, extraction solvent, drug-to-extract ratio, and oleuropein content per dose make comparison possible; a label saying only “olive leaf extract” does not.

Quality standards exist for the raw material: the European Pharmacopoeia requires dried olive leaf to contain at least 5% oleuropein, and there is a separate pharmacopoeia standard for olive leaf dry extract. Beware of doubling up. In the case reported by Shaw, a woman already taking one olive leaf supplement added a combination hay fever product that also contained olive leaf, reaching the equivalent of 5.5 g of dried leaf a day. Olive oil is a different product with a different claim. Under EU Regulation 432/2012, olive oil may carry the claim that “olive oil polyphenols contribute to the protection of blood lipids from oxidative stress” only if it contains at least 5 mg of hydroxytyrosol and its derivatives per 20 g, the daily amount needed for the effect. EFSA noted that some olive oils are too low in polyphenols to reach that, and its approval concerned oil, not leaf extracts or capsules.