Oleuropein

Oleuropein: A Comprehensive Reference

1. Identity, Nomenclature, and Natural Sources

Chemical Identity

Oleuropein is a glycosylated seco-iridoid, a bitter phenolic compound found in green olive skin, flesh, seeds, and leaves. More precisely, oleuropein is a derivative of elenolic acid linked to the orthodiphenol hydroxytyrosol by an ester bond and to a molecule of glucose by a glycosidic bond. The term oleuropein is derived from the botanical name of the olive tree, Olea europaea. Its molecular formula is C₂₅H₃₂O₁₃, and it carries PubChem CID 5281544. The compound is thus structurally composed of three subunits: a polyphenol, namely 4-(2-hydroxyethyl)benzene-1,2-diol — also known as hydroxytyrosol (HT) — a secoiridoid called elenolic acid, and a glucose molecule.

Within the broader classification of olive phenolics, oleuropein belongs to the secoiridoids, alongside ligstroside; other phenolic classes in olive include phenolic acids, phenolic alcohols (tyrosol and hydroxytyrosol), hydroxy-isocromans, flavonoids, and lignans.

Botanical Source and Distribution

The olive tree (Olea europaea) is native to the Mediterranean region, and both the oil and the fruit are some of the main components of the Mediterranean diet. Oleuropein is the most abundant phenolic compound in all parts of olive trees (Olea europaea L.), particularly concentrated in olive leaves. Oleuropein is the major bioactive compound of Olea europaea, widely known as the olive tree, and is present in high amounts in unprocessed olive fruit and leaves. During maturation of fruit or as a result of olive processing (such as oil production), chemical and enzymatic reactions occur which reduce the concentration of oleuropein and raise the concentration of hydroxytyrosol, which is the principal degradation product of oleuropein.

Oleuropein is the major bioactive antioxidant found in all parts of the olive tree (Olea europaea L.) and the most abundant polyphenol in olive leaves, reaching an oleuropein content of 10–20% of their dry mass. These potential health benefits of olive leaves are mostly related to low molecular weight polyphenols such as oleuropein (up to 60–90 mg/g dry leaf weight), hydroxytyrosol, tyrosol, tocopherol, elenolic acid derivatives, caffeic acid, p-coumaric acid, and vanillic acid, as well as flavonoids.

Oleuropein is a polyphenol found in the fruit, the roots, the trunk, and more particularly in the leaves of plants belonging to the Oleaceae family, and especially Olea europaea. Because of its bitter taste and astringency, oleuropein must be partially removed or decomposed to make olives edible. During processing of bitter and inedible green olives for consumption as table olives, oleuropein is removed from olives via a number of methods, including by immersion in lye.

Common Forms and Preparations

In commerce and research, oleuropein is most commonly delivered via olive leaf extract (OLE), a concentrated preparation of the dried leaves of Olea europaea. Olive leaf extracts vary enormously in their concentration of oleuropein — from as little as 1% to as high as 40% of the total extract. Dried olive leaf is about 6% oleuropein, while extracts (the most common form in supplements) provide about 1% to 40% oleuropein.

The extract is available commercially as capsules, liquid tinctures, teas, and topical preparations, with standardized supplements typically providing 15–40% oleuropein per dose. Specifically:

• Capsules and tablets: The most common supplement form. Capsules typically contain 250–500 mg of standardized extract per dose, with oleuropein content ranging from 15% to 40% of the total extract.
• Liquid extracts and tinctures: Available as olive leaf concentrate or ethanol-based tinctures. Liquid forms are dosed at 500–1,000 mg equivalent daily, typically taken as drops or mixed into beverages. One well-studied liquid product provided 136.2 mg of oleuropein and 6.4 mg of hydroxytyrosol daily. Liquid forms may offer faster absorption due to pre-solubilization but lack the standardization consistency of capsules.
• Teas and infusions: Traditional preparation involves steeping 1–2 teaspoons (1–2 g) of dried olive leaves in hot water for 10–15 minutes, consumed 2–3 times daily. Tea preparations yield a mildly bitter infusion with lower and more variable oleuropein content compared to standardized extracts.

Oleuropein may also be used for chemical standardization of the plant and its extracts of medicinal interest. The extraction process matters substantially: the highest oleuropein content in extracted preparations is achieved by freeze drying, followed by air drying at room temperature.

2. Traditional and Historical Use

Ancient Egypt and the Near East

The use of the products derived from the olive tree on human health dates back centuries, and in several civilizations the olive tree had and still has a very strong cultural and religious symbolism. Olive leaves were used to treat a range of diseases in ancient times, including malaria fever and lower earaches. Although it was not understood at the time what key components were responsible for these effects because they had not yet been discovered, oleuropein is now recognized as one of the primary elements in immature olive fruits and leaves.

Mediterranean and European Folk Medicine

Olive leaves (Olea europaea) have been used by traditional Mediterranean medical practitioners for thousands of years, most often in poultices and decoctions to reduce fever and fight infection. Olive oil and olive leaf extract are renowned natural traditional remedies used for the treatment of different conditions, including dermatitis, wound healing and treatment of burns, stomach and intestinal pain, malaria-induced fever, different infections, alopecia, rheumatic pain, otitis, rickets, distortions, sciatica, hypertension, as a diuretic, as a laxative, and as an aphrodisiac.

According to botanist James A. Duke, Iranians use an olive leaf decoction to cure coughs, while in Algeria, olive leaves are chewed to relieve toothaches. In Mediterranean folk medicine, the preparation of olive leaf has been used as a common tonic for gout. In Mediterranean folk medicine, the preparation of olive leaf has been used as a common tonic for gout.

In the Middle Ages, the medical nun Hildegard von Bingen is said to have treated gastrointestinal problems and high blood pressure with olive leaf tea. Furthermore, medical-pharmaceutical records from the 19th century contain information about the use of olive leaf extract to treat fevers. Even then, a bitter ingredient was suspected to be the healing substance — today this substance is known as oleuropein.

Modern Identification

The 19th and 20th centuries saw a renewed interest in olive leaf, spurred by scientific research validating its traditional uses. Modern studies identified oleuropein, a key compound in olive leaf, as a potent antioxidant and anti-inflammatory agent. Oleuropein was discovered in 1908. It was later identified as the compound responsible for the fever-reducing and antimicrobial activities long attributed to olive leaf preparations.

3. Key Constituents and Active Compounds in Olive Leaf

Although oleuropein is the dominant bioactive, olive leaf extract contains a complex mixture of phenolic compounds. The leaves contain a rich array of phenolic compounds — including oleuropein, hydroxytyrosol, tyrosol, verbascoside, and flavonoids such as luteolin and quercetin — at concentrations far exceeding those found in olive fruit or olive oil. The most abundant components of OLE are oleuropein, hydroxytyrosol, oleacein, and oleuropein-aglycone. Oleuropein is the most concentrated, followed by hydroxytyrosol; oleacein and oleuropein-aglycone are also present at high concentrations.

Upon ingestion, oleuropein undergoes biotransformation. Upon ingestion, oleuropein is hydrolyzed in the body into several other bioactive molecules, including elenolic acid and hydroxytyrosol. Hydroxytyrosol, in particular, is recognized as one of the most potent natural antioxidants. A portion of a dose of oleuropein can be absorbed as such in the intestinal upper level, and another portion can reach the colon where it would mainly be absorbed after bioconversion into hydroxytyrosol and/or an intermediate metabolite such as oleuropein aglycone or hydroxytyrosol acetate.

4. Established Mechanisms of Action

Antioxidant Activity

Oleuropein and its metabolite hydroxytyrosol have powerful antioxidant activity, which might be responsible for some of olive oil's antioxidant, anti-inflammatory, and disease-fighting activities. Having the catechol functional group, oleuropein as a phenolic compound is structurally optimized for antioxidant activity. The compound scavenges reactive oxygen species (ROS) and can upregulate endogenous antioxidant defenses.

Anti-inflammatory Mechanisms

Oleuropein exerts anti-inflammatory and anti-oxidant effects via down-regulation of MAPK and NF-κB signaling pathways and induction of Nrf2-linked HO-1, controlling the production of inflammatory mediators and decreasing IL-6 and TNF-α cytokines. More specifically, this anti-inflammatory effect is mediated via inhibitory action on NF-κB translocation to the nucleus, cyclo-oxygenase-2 (COX-2), caspase-3, and iNOS. Oleuropein also attenuates the release of several inflammatory mediators. MAPKs and NF-κB activations are drastically down-regulated by oleuropein, whereas Nrf2 and HO-1 protein expressions are up-regulated.

Cardiovascular Mechanisms

Oleuropein is best known for its blood pressure-lowering effect. When administered via intraperitoneal or intravenous injections, oleuropein significantly reduces systolic and diastolic blood pressure in animal models. The ability of oleuropein to lower blood pressure may justify the traditional use of olive leaf in the treatment of mild to moderate hypertension. The hypotensive mechanism involves enhanced nitric oxide production, which promotes vasodilation and reduces vascular resistance.

The phenolic fraction extracted from the leaves of the olive tree, which contains significant amounts of oleuropein, prevents lipoprotein oxidation. In addition, oleuropein has shown cardioprotective effect against acute adriamycin cardiotoxicity and anti-ischemic and hypolipidemic activities.

Anti-diabetic Mechanisms

Preclinical studies indicate that oleuropein improves glucose transport, increases insulin sensitivity, and facilitates insulin secretion by pancreatic β-cells, thereby supporting the hypothesis of the possible benefits for the control of hyperglycemia. In addition to the effects on metabolic pathways and insulin sensitivity, oleuropein facilitates glucose-stimulated insulin secretion by pancreatic β-cells. The evidence suggests that oleuropein targets skeletal muscle and enhances glucose uptake and its related protein signaling cascades, improving glucose tolerance and insulin sensitivity.

Anticancer Mechanisms

Current research has shown that oleuropein acts as an anticancer agent by several major mechanisms, including targeting HER2, epigenetic modifications, interfering with the MAPK pathway, modulation of apoptosis and PI3K/AKT signaling axis, as well as by reducing ROS production. These compounds have the ability to inhibit cell proliferation, induce cell death (apoptosis, autophagy, and necrosis), inhibit angiogenesis, suppress tumor metastasis, and modulate cancer-associated signaling pathways.

Antimicrobial Mechanisms

The ortho-diphenol structure of oleuropein has been shown to be the active agent of its antimicrobial mechanism. However, the precise molecular mechanisms underlying oleuropein's antimicrobial activity are still unclear.

Autophagy Induction and Protein Aggregation Inhibition

Oleuropein and its isoforms, including oleuropein aglycone (OleA), may exert antioxidant and anti-inflammatory activities, but also other peculiar actions as autophagy inducers and amyloid fibril growth inhibitors. These additional mechanisms are of particular relevance to neurodegenerative disease research.

5. Scientific Evidence by Area of Use

5.1 Cardiovascular Health: Blood Pressure

Blood pressure modulation is among the best-studied human applications of oleuropein-containing olive leaf extract.

Twin study (preliminary clinical, Germany): In a preliminary clinical study carried out in 20 monozygotic adult twin pairs with mild hypertension in Germany, EFLA®943 treatment at a dose of 500 or 1000 mg daily for 8 weeks demonstrated a significant reduction of subjects' systolic and diastolic blood pressure. At a dose of 1000 mg daily, the extract was clearly superior to recommendations for lifestyle changes in reducing mean blood pressure levels from baseline.

Susalit et al. (RCT, 2011) — Comparison with captopril: One clinical trial in patients with stage 1 hypertension used an olive leaf extract dosage of 500 mg twice daily for 8 weeks. This randomized clinical trial compared olive leaf extract with captopril (an ACE inhibitor) in reducing systolic blood pressure, and found the extract non-inferior to low-dose captopril at the tested dose.

Pheno-enriched OLE RCT (published in European Journal of Nutrition): The commercial product used in this study was standardized to contain 6.81 mg oleuropein/mL and 0.32 mg hydroxytyrosol/mL, providing 136.2 mg oleuropein and 6.4 mg hydroxytyrosol per day. This data demonstrated that OLE has the potential to significantly reduce 24-h and daytime systolic blood pressure (SBP) and 24-h and daytime diastolic blood pressure (DBP) relative to control. The magnitude of BP changes observed (SBP by 3.33 and 3.95 mmHg and DBP by 2.42 and 3.00 mmHg for 24-h and daytime values respectively) can be considered physiologically significant.

Large observational open pilot study: An open pilot study assessed the effect of 2-month supplementation of a combination of olive leaf and fruit extracts (Tensiofytol®) in the clinical management of hypertension and metabolic syndrome. A total of 663 (pre-)hypertensive patients were enrolled by general practitioners and supplemented for two months with two capsules per day (100 mg/d of oleuropein and 20 mg/d of hydroxytyrosol). Systolic and diastolic blood pressures were measured before and after treatment, alongside markers of metabolic syndrome including HDL-C, triglycerides, fasting blood glucose, and waist circumference.

Evidence characterization: Evidence for a modest blood pressure-lowering effect of OLE in humans is encouraging but not definitive. Previous studies have indicated potential blood pressure and lipid-lowering effects of OLE in humans, but results have thus far lacked consistency, perhaps due to differences in phenolic dose, duration, and study design. Most trials are small, short-term, and lack blinding consistency.

5.2 Cardiovascular Health: Lipid Profile

In pre-hypertensive males, a significant decrease in total cholesterol, LDL-cholesterol, and triglyceride levels was observed after OLE (containing 136 mg oleuropein and 6 mg hydroxytyrosol) intake for 6 weeks. Supplementation with OLE containing 200 mg oleuropein for 8 weeks in patients with stage-1 hypertension also resulted in reduced total cholesterol, LDL-cholesterol, and triglyceride levels. A decrease in LDL-cholesterol was shown after 8 weeks of supplementation with OLE at dosages containing 104 and 208 mg oleuropein in monozygotic twins with mild hypertension.

Evidence characterization: Results across lipid-lowering trials are inconsistent. Evidence from previous studies has shown that extracts from olive leaf can improve lipid profiles, although the outcomes and their effect sizes differ between studies. Human clinical trial evidence remains limited by small sample sizes and variable product standardization.

5.3 Glycemic Control and Diabetes

Clinical crossover study (healthy subjects): The post-prandial glycemic profile was investigated in a crossover study of 25 healthy subjects randomly allocated to a Mediterranean diet with or without supplementation of oleuropein (20 mg). Two hours after the meal, subjects who ate oleuropein supplements had a significantly lower blood glucose and dipeptidyl-peptidase 4 (DPP-4) protein concentration and activity, and higher serum insulin and glucagon-like peptide-1 (GLP-1) levels.

Crossover study (overweight men): Supplementation with olive leaf extract equating to a daily dose of oleuropein 51.1 mg and hydroxytyrosol 9.7 mg for 12 weeks was examined in a crossover study evaluating effects on insulin action and cardiovascular risk factors in men with a BMI of 28 (±2) kg/m².

Preclinical evidence: A study demonstrated that treatment with oleuropein in a streptozotocin-induced diabetic animal model improved hyperglycemia, significantly reduced fasting blood glucose (FBG) level, glycated hemoglobin (HbA1c), and improved glucose tolerance. Another study showed that oleuropein inhibited the activity of glucose-6-phosphatase in the liver, increased serum insulin, and enhanced the antioxidant activity of pancreatic tissue by increasing glucose uptake in isolated psoas major muscles.

Evidence characterization: On the clinical side, the available evidence is still preliminary and requires more extensive investigations. Many questions remain unanswered regarding the potential benefits of oleuropein in diabetes prevention and treatment. These questions should be addressed in appropriately designed studies in the future. Most diabetes-related evidence remains in the preclinical (animal and in vitro) stage.

5.4 Antimicrobial Activity

Oleuropein has several pharmacological properties, including antioxidant, anti-inflammatory, anti-atherogenic, anti-cancer, antimicrobial, and antiviral properties, and for these reasons it is commercially available as a food supplement in Mediterranean countries.

In vitro antibacterial and antifungal activity: The minimum inhibitory concentration (MIC) and minimum fungicidal/bactericidal concentration (MFC/MBC) for oleuropein were found to be 65 mg/mL and 130 mg/mL, respectively. Oleuropein significantly inhibited biofilm formation at sub-MIC concentrations. RT-qPCR indicated significant down-regulation of expression of genes involved in biofilm formation in Candida albicans (Hwp1, Als3) and Candida glabrata (Epa1, Epa6) as well as Escherichia coli (LuxS, Pfs) genes after culture with a sub-MIC of oleuropein.

Research has also demonstrated that olive leaf extracts play a role in regulating the composition of the gastric flora by selectively reducing levels of H. pylori and C. jejuni.

5.5 Antiviral Activity

Oleuropein possesses a well-documented antiviral activity. Its efficacy against hemorrhagic septicemia rhabdovirus (VHSV), hepatitis B virus (HBV), and human immunodeficiency virus (HIV) has been demonstrated. It has been claimed in a U.S. patent that oleuropein has potent antiviral activities against herpes mononucleosis, hepatitis virus, rotavirus, bovine rhinovirus, canine parvovirus, and feline leukemia virus. Studies have also shown that oleuropein exhibits a significant antiviral activity against respiratory syncytial virus and para-influenza type 3 virus.

Evidence characterization: Antiviral evidence is predominantly in vitro and based on cell culture and animal models. There are no published, adequately powered human randomized controlled trials evaluating oleuropein's antiviral efficacy in clinical infections.

5.6 Anticancer Activity

Oleuropein consumption has aided in cancer treatment, and this was assumed to be owing to its antioxidant properties. Oleuropein's effects on cancer go beyond antioxidant action; it is now known that oleuropein functions as both an anti-proliferative and an apoptotic promoter in many cancer cells.

Breast cancer cell studies: Following oleuropein treatment at various IC50 doses, the proliferation of in vitro MCF-7 breast cancer cells diminishes in a time-dependent manner. Oleuropein's anti-proliferative action has been established in numerous studies using MCF-7 cell lines. In vivo studies on mice that were subcutaneously injected with MCF-7 and given 125 mg/kg of oleuropein in their food revealed that it suppresses peri-pulmonary and parenchymal lung metastases.

Melanoma cell studies: Oleuropein was able, at a dose of 500 µM, to stimulate apoptosis in A375 human melanoma cells, while at a non-toxic dose of 250 µM it affected cell proliferation and induced the downregulation of the pAKT/pS6 pathway. At 250 µM, oleuropein succeeded in increasing the cytotoxic effect of dacarbazine (DTIC). The major effect was found in the association between oleuropein and everolimus (RAD001), also on PLX4032-resistant BRAF melanoma cells.

Leukemia/lymphoma in vitro study: OLE inhibited cell proliferation and induced apoptosis in B-acute lymphoblastic leukemia (B-ALL) and, to a lesser extent, in lymphomas and acute myeloid leukemia (AML) cell lines.

Evidence characterization: Anticancer evidence is primarily preclinical (cell culture and animal models). Experimental evidence about oleuropein's bioavailability in humans and animals clearly demonstrates that oleuropein and hydroxytyrosol act as cancer-preventive agents and cytotoxic drugs mainly at concentrations far from plasma levels reachable through nutrition. No human clinical trials have evaluated oleuropein as a cancer treatment. The bioactivities summarized in published research support epidemiological evidence demonstrating a negative correlation between olive oil consumption and cancer risk, but the causal contribution of oleuropein specifically remains to be established in clinical settings.

5.7 Neuroprotection

Oleuropein and its aglycone may exert protective effects in neurodegeneration through autophagy induction and amyloid fibril growth inhibition, mechanisms of direct relevance to Alzheimer's and Parkinson's disease pathology. Oleuropein has been investigated in conditions such as neurodegenerative and cardiovascular diseases, diabetes mellitus, and chronic kidney diseases, by its putative antioxidant and anti-inflammatory activity, but also for its peculiar actions as an autophagy inducer and amyloid fibril growth inhibitor.

Evidence characterization: Neuroprotection evidence is currently limited to animal models and in vitro studies. There are still numerous key issues that need to be answered, and what the neuroprotective roles of oleuropein are in conditions such as dementia, Parkinson's, Alzheimer's, and schizophrenia remains an unanswered question.

5.8 Systemic Review Evidence (RCTs)

A 2024 systematic review analyzed 12 human randomized controlled trials (RCTs), involving 683 participants, to assess the effects of supplements, pure compounds, or enriched foods containing oleuropein and hydroxytyrosol regarding systemic health outcomes, including CVD risk factors, liver parameters, and bone, joint, and cognitive health. The review found contrasting but encouraging results, with some studies reporting significant modulation of body weight, lipid profile, and glucose metabolism, and improvements in bone, joint, and cognitive functions.

This targeted approach revealed health benefits covering glycemic control, blood pressure, inflammatory and oxidative markers, liver function, bone and joint health, and cognitive health, offering a comprehensive understanding of OLE's and hydroxytyrosol's impacts.

Overall evidence characterization: Despite the increasing number of published studies looking at the beneficial effects of oleuropein, there is limited clinical evidence focused on the benefits of this polyphenol as a nutraceutical product in humans, and many problems are still to be resolved about its bioavailability, bioaccessibility, and dosage. Future clinical randomized trials are needed to establish the relationship between the beneficial effects and the mechanisms of action occurring in the human body in response to the intake of oleuropein.

6. Body Systems and Health Areas of Association

• Cardiovascular system: Blood pressure regulation, LDL and lipid profile modulation, anti-atherogenic effects, protection against ischemia-reperfusion injury, and anti-thrombotic (antiplatelet) activity.
• Endocrine/metabolic system: Glucose homeostasis, insulin sensitivity, pancreatic β-cell function, anti-obesity effects (via PPARγ inhibition and adiponectin modulation), and protection against diabetic complications (nephropathy, cardiomyopathy).
• Immune and antimicrobial: Broad-spectrum in vitro activity against bacteria (including H. pylori), fungi (Candida species), and multiple viruses; modulation of inflammatory cytokines and innate immune pathways.
• Oncology (preclinical): Anti-proliferative and pro-apoptotic effects in multiple cancer cell lines; potentiation of chemotherapy in vitro; epidemiological correlation with lower cancer incidence in olive-oil-consuming populations.
• Nervous system (preclinical): Autophagy induction, amyloid fibril inhibition, neuroinflammation reduction, and potential protective effects in models of neurodegeneration.
• Gastrointestinal system: Traditional use for gastric complaints; in vitro regulation of gastric microflora.
• Musculoskeletal system: Anti-arthritic effects in animal models (via MAPK/NF-κB inhibition); preliminary evidence in bone and joint health from RCTs.

7. Dosage Forms and Doses Reported in Studies

Clinical trial dosages vary widely. The following are doses reported in published studies:

• One clinical trial in patients with stage 1 hypertension used an olive leaf extract dosage of 500 mg twice daily (1,000 mg/day) for 8 weeks.
• A preliminary clinical study in 20 monozygotic twin pairs used EFLA®943 at a dose of 500 or 1,000 mg daily for 8 weeks.
• One well-characterized RCT used a dose providing 136.2 mg oleuropein and 6.4 mg hydroxytyrosol per day.
• A pre-hypertensive male study used OLE containing 136 mg oleuropein and 6 mg hydroxytyrosol for 6 weeks.
• A stage-1 hypertension study used OLE containing 200 mg oleuropein for 8 weeks.
• A large observational open pilot study used 100 mg/d oleuropein and 20 mg/d hydroxytyrosol for two months in 663 (pre-)hypertensive patients.
• A crossover study used OLE equating to 51.1 mg oleuropein and 9.7 mg hydroxytyrosol daily for 12 weeks in overweight men.
• A Mediterranean diet crossover study used 20 mg oleuropein supplementation in 25 healthy subjects.
• Animal studies used oleuropein doses equivalent to a human dose of 61.5 mg/kg or 3.1 g of OLE consumption daily, while human studies used 50–136 mg OLE/day.
• Clinical trials have used various extracts providing 100 to 136.2 mg oleuropein daily from products standardized to about 1% to 40% oleuropein. To obtain 100 mg of oleuropein, one would need 250 mg of a 40% extract, 500 mg of a 20% extract, or 1,000 mg of a 1% extract.

8. Safety Considerations and Drug Interactions

General Safety Profile

Olive leaf extract appears to be generally safe and well-tolerated based on small clinical trials, although gastrointestinal symptoms can occur. Oleuropein is thought to be highly safe. High concentrations of oleuropein administered in vivo were demonstrated to be safe, and studies on rodents showed that it had an excellent safety profile. A moderate lethal dose of oleuropein has not been established in acute toxicity studies, because no side effects or lethal conditions have been observed in mice even at doses up to 1,000 mg/kg.

Olive leaf extract is classified as Generally Recognized as Safe (GRAS) by the FDA for use as a food ingredient, based on toxicological assessments supporting safe consumption of up to 100–150 mg of hydroxytyrosol per day.

Oleuropein's toxicity, as well as that of its two primary metabolites hydroxytyrosol and elenolic acid, was proven to be safe in a variety of animal kinds. Oleuropein's acute toxicity trials did not show any fatality or negative effects in mice, even at a concentration of 1,000 mg/kg.

Bioavailability Considerations

According to bioavailability studies, oleuropein is absorbed to a greater extent than 55–66 mol% in humans, and at least 5% is eliminated in the urine. Moreover, in less than 2 hours, oleuropein and its metabolites are identified at their highest levels in serum and urine. Olive leaf extract results in higher plasma concentrations when taken in liquid form compared to capsules. Although there was no significant difference in the peak hydroxytyrosol concentrations between the liquid and capsule forms, the peak concentration was reached earlier with the liquid preparation.

Drug Interactions: Antihypertensive Agents

Olive leaf may enhance the hypotensive effect of blood pressure-lowering agents or other herbal products with blood pressure-lowering effects. Combining olive leaf extract with medications for high blood pressure (e.g., beta-blockers, ACE inhibitors, calcium channel blockers) can have an additive effect, potentially causing blood pressure to drop to dangerously low levels (hypotension). Given that the 2011 clinical trial found blood pressure reductions with OLE comparable to low-dose captopril, additive hypotensive effects are plausible when OLE is combined with antihypertensive medications.

Drug Interactions: Antidiabetic Agents

Co-administration of olive leaf extract with drugs used to manage diabetes can increase the risk of hypoglycemia. Olive leaf extract may have additive hypoglycemic effects when combined with insulin, sulfonylureas, metformin, or other glucose-lowering medications.

Drug Interactions: Anticoagulants and Antiplatelet Agents

Oleuropein has been shown in some laboratory studies to have antiplatelet effects, meaning it can inhibit blood clot formation. Theoretically, taking olive leaf extract with anticoagulant drugs (like warfarin) or antiplatelet drugs (like aspirin or clopidogrel) could increase the risk of bleeding and bruising. However, activated partial prothrombin time was unaffected in at least one reported study, and direct pharmacokinetic interaction data with warfarin are sparse.

Pregnancy and Lactation

Information regarding safety and efficacy during pregnancy and lactation is lacking.

Hepatic Caution

Caution may be warranted in hepatic disease, as the liver is a primary site of oleuropein and polyphenol metabolism, and high-dose exposure in compromised hepatic function has not been adequately studied in humans.

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