Olive leaf extract

What it is

Olive leaf extract is made from the leaves of the olive tree, mainly in the Mediterranean region. The leaves are rich in phenolic compounds, of which oleuropein is the most abundant. Commercial extracts are produced by drying and milling the leaf and then extracting it with water, methanol mixtures or hexane. It is sold as tablets and capsules, most often marketed for immune support and for blood pressure.

What the research says

The evidence is real but thin and low-certainty. Two independent meta-analyses agree that olive leaf extract lowers systolic blood pressure by a few mmHg on average, and one also finds small reductions in triglycerides. The comparison that showed a benefit used 500 mg a day; at 1,000 mg a day one trial found no difference from captopril, an ACE inhibitor, and another found no difference from placebo for a combined formulation. The trials are few and small, several were funded by manufacturers, and the review that tested both doses grades every one of its three comparisons low certainty. Effects on blood glucose, liver, kidney and inflammatory markers were not found.

Evidence grade: Limited evidence.

What goes wrong

New Zealand's medicines safety authority has received spontaneous reports of gastrointestinal adverse reactions to olive leaf extract products, including one case of nausea, epigastric pain and projectile vomiting followed by diarrhoea. (Source 1)

• Case series, Very low certainty.
• Size: 3 spontaneous reports to the Centre for Adverse Reactions Monitoring.
• Who: New Zealand consumers of olive leaf extract products.
• How long: Reactions described as occurring soon after taking the product.
• Result: Three reports of gastrointestinal adverse reactions; one with nausea, epigastric pain, projectile vomiting and bouts of diarrhoea, the others with vomiting or gastrointestinal pain. Spontaneous reports cannot establish causation or a rate.
• Funding: government regulator, no commercial funding.

Limit of this finding: Three spontaneous reports are a safety signal, not a rate. Nobody counted how many people took the product, and no one established that olive leaf extract caused the symptoms. This tells you gastrointestinal reactions have been reported, and nothing about how likely they are.

The Centre for Adverse Reactions Monitoring (CARM) has received three reports of gastrointestinal adverse reactions with the use of olive leaf extract products.

Position: Medsafe (New Zealand), 2 September 2015, reminds prescribers that olive leaf extract is a dietary supplement marketed for immune support that can contain pharmacologically active ingredients capable of causing adverse reactions. (Source 1)

• Official position, Certainty not rated.
• Size: Not applicable.
• Who: New Zealand healthcare professionals and consumers.
• How long: Published 2 September 2015.
• Result: A regulator's safety communication, not a study. It is recorded here as a position with its date and does not substitute for trial evidence.
• Funding: government regulator.

Healthcare professionals are reminded that dietary supplements can contain pharmacologically active ingredients that may cause adverse reactions.

What the evidence supports

A systematic review with GRADE found that 500 mg a day of olive leaf extract lowered systolic blood pressure compared with placebo or no treatment, but did not change diastolic blood pressure. (Source 2)

• Systematic review, Low certainty.
• Size: 5 trials, 325 patients (the 500 mg comparison is a subset)
• Who: Adults aged 18-80 with prehypertension or hypertension.
• How long: At least 8 weeks of follow-up.
• Result: Systolic BP mean difference −5.78 mmHg, 95% CI [−10.27 to −1.30] across the three trials in this comparison; no significant change in diastolic BP. The review rates the certainty of evidence for this comparison as low, and says the limited number of participants prevents a robust conclusion.
• Funding: industry-funded in part - the review records that three of the included trials declared funding from natural health manufacturers.

Limit of this finding: This is one of three separate comparisons in the review, and it rests on three small trials drawn from a total of 325 patients in five trials. The review grades the certainty of the evidence for this comparison as low, which means further research could easily change the number. An average fall of 5.78 mmHg from trials this small is a starting point, not a settled effect.

The second comparison, 500 mg per day of olive leaf extract versus placebo or no treatment, showed a significant reduction in systolic BP over a period of at least 8 weeks of follow up (MD −5.78 mmHg, 95% CI [−10.27 to −1.30]) and no significant changes on diastolic BP.

A separate meta-analysis of twelve randomised trials found small average reductions in systolic blood pressure and triglycerides with olive leaf extract in the general adult population. (Source 3)

• Meta-analysis, Moderate certainty.
• Size: 12 studies, 819 participants.
• Who: General adult population, with subgroups for hypertension and normal weight.
• How long: Not stated in the abstract.
• Result: Triglycerides WMD -9.51 mg/dl (95% CI -17.83, -1.18; P = 0.025; I2 = 68.7%); systolic BP WMD -3.86 mmHg (95% CI -6.44, -1.28; P = 0.003; I2 = 19.9%). The review rates certainty as moderate for blood pressure and lipids and low to very low for glucose, liver, kidney and inflammatory outcomes; three of the twelve trials were at high risk of bias.
• Funding: not stated in the material we could read.

Limit of this finding: The certainty ratings in this review are split by outcome, and the passage this batch first recorded quoted only the low end. Blood pressure and the lipid measures, including triglycerides, are rated moderate quality; HbA1c and the inflammatory markers are rated very low. The two significant effects are also small: about 3.86 mmHg off systolic pressure and about 9.51 mg/dl off triglycerides. A 3.86 mmHg average sits inside the range ordinary blood pressure measurement varies by, so this is not a blood pressure treatment, and the triglyceride result came with substantial disagreement between trials (I2 = 68.7%).

Overall analyses showed that OLE supplementation significantly decreased triglyceride (TG) levels (WMD = − 9.51 mg/dl, 95% CI − 17.83, − 1.18; P = 0.025; I2 = 68.7%; P-heterogeneity = 0.004), and systolic blood pressure (SBP) (WMD = − 3.86 mmHg, 95% CI − 6.44, − 1.28 mmHg; P = 0.003; I2 = 19.9%; P-heterogeneity = 0.28).

What the evidence does not support

At 1,000 mg a day, olive leaf extract was no different from captopril, an ACE inhibitor, in the one trial that tested it; a separate 1,000 mg comparison against a real placebo also found no significant blood pressure change. (Source 2)

• Systematic review, Low certainty.
• Size: Part of the 5 trials, 325 patients included.
• Who: Adults with prehypertension or hypertension; the 1,000 mg comparison is a single trial.
• How long: At least 8 weeks.
• Result: The abstract reports systolic BP falling 11.5 mmHg on olive leaf extract against 13.7 mmHg in the arm it labels placebo (MD 2.2 mmHg, 95% CI [−0.43–4.83]) and diastolic BP 4.8 against 6.4 mmHg (MD 1.60 mmHg, 95% CI [−0.13–3.33]) — neither significant. The review's own methods record that the single trial in this comparison gave the control group captopril, and its results section heads the comparison 'Olive leaf extract vs antihypertensive drug'. The review's separate 1,000 mg comparison, a combined olive leaf formulation against a true placebo, also found no significant change in systolic or diastolic BP. Certainty rated low.
• Funding: industry-funded in part - three included trials declared funding from natural health manufacturers.

Limit of this finding: The review's abstract mislabels this comparison. It calls it '1,000 mg per day of olive leaf extract versus placebo', but the same abstract, two sentences later, calls it '1,000 mg per day of olive leaf extract versus captopril', and the paper's methods state that the one trial involved (Susalit et al., 2011) gave captopril to the control group. So the 13.7 mmHg fall labelled 'placebo' was produced by a blood pressure drug, not by a dummy tablet. What this comparison actually shows is that 1,000 mg of olive leaf extract was not measurably different from an ACE inhibitor in one small trial. Do not read it as 'no better than placebo', and do not read the 13.7 mmHg as what a placebo does. The review's separate comparison of a 1,000 mg combined formulation against a genuine placebo found no significant blood pressure change either.

The third comparison, 1,000 mg per day of olive leaf extract versus placebo shows no significant difference but an almost similar reduction in systolic BP (−11.5 mmHg in olive leaf extract and −13.7 mmHg in placebo, MD 2.2 mmHg, 95% CI [−0.43–4.83]) and diastolic BP (−4.8 mmHg in olive leaf extract and −6.4 mmHg in placebo, MD 1.60 mmHg, 95% CI [−0.13–3.33]).

Pooling twelve randomised trials, olive leaf extract produced no meaningful change in glucose metabolism, liver and kidney markers or inflammatory markers. (Source 3)

• Meta-analysis, Low certainty.
• Size: 12 studies, 819 participants overall; 7 studies and 520 participants for total cholesterol.
• Who: General adult population.
• How long: Not stated in the abstract.
• Result: No meaningful change in glucose homeostasis, liver, kidney or inflammatory markers across the twelve trials. The review's body also reports a meta-analysis of seven trials and 520 participants finding no significant overall effect on total cholesterol, with reductions in total cholesterol appearing only in the hypertensive (− 9.14 mg/dl) and normal-weight (− 6.69 mg/dl) subgroups. Under GRADE the review rates total cholesterol, the other lipids and blood pressure as moderate quality evidence and rates HbA1c, hs-CRP, TNF-alpha, IL-6 and IL-8 as very low.
• Funding: not stated in the material we could read.

Limit of this finding: These nulls are not all equally certain. The review's GRADE table rates total cholesterol, the other lipids and blood pressure as moderate quality evidence, so the absence of an overall total-cholesterol effect is reasonably well established. The glucose, liver, kidney and inflammatory results are rated low to very low, which means those nulls could change with better trials rather than being settled.

However, no meaningful changes were seen in glucose hemostasis, liver and kidney, or inflammatory markers.

Where the research disagrees

Whether olive leaf extract can be said to improve the cardiometabolic profile

• Nediani and colleagues' PeerJ systematic review (2021), systematic-review: The results from this review suggest the reduction of systolic BP, LDL and inflammatory biomarkers, but it may not provide a robust conclusion regarding the effects of olive leaf extract on cardiometabolic profile due to the limited number of participants in the included trials. (Source 2)
• The Diabetology & Metabolic Syndrome meta-analysis (2022), meta-analysis: As the quality of evidence for glucose hemostasis variables, liver, kidney, and inflammatory markers, were low-to-very low, higher quality RCTs may impact the overarching results. (Source 4)

How much

• Reference intake: No reference intake (RDA or AI) exists for olive leaf extract. It is a marketed dietary supplement rather than an essential nutrient; Medsafe describes it as a dietary supplement predominantly marketed to provide immune support. (Source 1)
• Upper limit: No upper limit or acceptable daily intake was found. Neither systematic review we read reports one, and the EFSA opinion on olive leaf water extract and glucose tolerance could not be retrieved (both efsa.europa.eu and the EFSA Wiley mirror returned HTTP 403). (Source 2)
• Studied: 500 mg per day across three trials, given as one 500 mg tablet once daily or a 250 mg tablet twice daily, for at least 8 weeks - the comparison that lowered systolic blood pressure. (Source 5)
• Studied: 1,000 mg per day in two trials: one gave a 500 mg olive leaf extract tablet twice daily against captopril, the other a combined formulation of 500 mg olive leaf extract with green coffee bean extract and beetroot twice daily against placebo. Neither produced a significant blood pressure difference. (Source 5)

A common belief, and what the research shows

The belief: More olive leaf extract means a bigger drop in blood pressure, so a 1,000 mg dose beats a 500 mg one.

What the research shows: The review that looked at both doses does not show that, but it is easy to misread, because its own abstract mislabels one comparison. At 500 mg a day against placebo or no treatment there was a significant fall in systolic pressure. At 1,000 mg a day the abstract says the comparison "shows no significant difference but an almost similar reduction in systolic BP (−11.5 mmHg in olive leaf extract and −13.7 mmHg in placebo, MD 2.2 mmHg, 95% CI [−0.43–4.83])" — but the comparator in that single trial was captopril, a blood pressure drug, not a placebo, as the same abstract admits when it reports "1,000 mg per day of olive leaf extract versus captopril" for the secondary outcomes. So the honest reading is that 1,000 mg was not measurably different from an ACE inhibitor in one small trial, and that a separate 1,000 mg comparison against a genuine placebo found no significant change either. The review's own summary of the whole body of evidence is that "The results from this review suggest the reduction of systolic BP, LDL and inflammatory biomarkers, but it may not provide a robust conclusion regarding the effects of olive leaf extract on cardiometabolic profile due to the limited number of participants in the included trials." It grades each of its three comparisons as low certainty.

Questions and answers

What is it?

Olive leaf extract is made from the leaves of the olive tree, Olea europaea, grown mainly around the Mediterranean. The leaves are unusually rich in phenolic compounds, and the most abundant of these is oleuropein, followed by hydroxytyrosol and several flavone glucosides. Oleuropein is what most products are standardised to. (Source 6)

What does it do in the body?

In pooled randomised trials it produces a small average fall in systolic blood pressure and in triglycerides. The averages are a few mmHg and a few mg/dl, measured in short trials, and the same pooling found nothing for glucose, liver, kidney or inflammatory markers. (Source 3)

Is it good or bad for you?

Neither, cleanly. The signal for blood pressure is consistent across two reviews but small, from few and small trials, some manufacturer-funded, and graded low certainty. Against that, spontaneous reports of gastrointestinal reactions exist, and trial safety bloods showed no liver or kidney changes. (Source 2)

How do you get more of it?

In the trials people took tablets: 500 mg a day as a single tablet or as 250 mg twice daily, or 1,000 mg a day as 500 mg twice daily. Those are what the studies gave participants, not a recommendation. The 500 mg comparison was the one that lowered blood pressure; the 1,000 mg trials were compared against captopril and against placebo and showed no significant difference. (Source 5)

If it is harmful, what reduces it?

It is taken deliberately rather than accumulated, so stopping the supplement removes the exposure. In the reported adverse reactions the gastrointestinal symptoms began soon after the product was taken, which is the pattern that leads reporters to stop it. (Source 1)

Why might someone be low in it or missing it?

Does not apply. Olive leaf extract is a marketed dietary supplement, not an essential nutrient, so there is no such thing as being deficient in it. Someone simply has none unless they buy and take it, or eat olive leaf material. (Source 1)

Which whole foods contain it or feed it?

Olive leaves are not a normal food; the extract is manufactured from dried, milled leaf. One place people do encounter olive leaf unknowingly is in adulterated dried oregano, where olive leaf is the commonest undeclared filler - in a 2024 analysis 2 of 15 retail oregano samples were adulterated with it. (Source 7)

What happens if you do not have it?

Nothing is described. There is no deficiency state for olive leaf extract, and the literature only studies what happens when it is added. The most that can be said is that in trials of adding it, several measured outcomes did not change at all. (Source 3)

We searched: Searched for olive leaf extract or oleuropein deficiency and essential-nutrient status via WebSearch; the two systematic reviews located (PeerJ 2021, Diabetology & Metabolic Syndrome 2022) study supplementation only and report no deficiency state.

How can you test for it?

No validated test of a person's olive leaf extract or oleuropein status was found in the literature we searched. Trials measured downstream outcomes instead - blood pressure, lipids, glucose, and liver and kidney bloods as safety checks. (Source 2)

We searched: Searched for olive leaf extract biomarker, oleuropein plasma level test and olive leaf status assay via WebSearch; neither systematic review reports a status test, and the PeerJ review's only laboratory measures of safety are creatinine, ALT and AST.

References

1. Medsafe (New Zealand Medicines and Medical Devices Safety Authority), Prescriber Update. Complementary Corner — Olive Leaf Extract. 2015. Read the source
2. PeerJ. Olive leaf extract effect on cardiometabolic profile among adults with prehypertension and hypertension: a systematic review and meta-analysis. 2021. DOI 10.7717/peerj.11173. Read the source
3. Diabetology & Metabolic Syndrome. The effects of olive leaf extract on cardiovascular risk factors in the general adult population: a systematic review and meta-analysis of randomized controlled trials - abstract, Results. 2022. DOI 10.1186/s13098-022-00920-y. Read the source
4. Diabetology & Metabolic Syndrome. The effects of olive leaf extract on cardiovascular risk factors in the general adult population: a systematic review and meta-analysis of randomized controlled trials - abstract, Conclusion. 2022. DOI 10.1186/s13098-022-00920-y. Read the source
5. PeerJ. Olive leaf extract effect on cardiometabolic profile among adults with prehypertension and hypertension: a systematic review and meta-analysis. 2021. DOI 10.7717/peerj.11173. Read the source
6. PeerJ. Olive leaf extract effect on cardiometabolic profile among adults with prehypertension and hypertension: a systematic review and meta-analysis. 2021. DOI 10.7717/peerj.11173. Read the source
7. Foods. Detection of Adulterated Oregano Samples Using Untargeted Headspace–Gas Chromatography–Ion Mobility Spectrometry Analysis. 2024. DOI 10.3390/foods13040516. Read the source