Olive Leaf Extract: Evidence, Dosage & Safety (UK)

Olive leaf extract is a dry powder derived from the leaves of Olea europaea — the same tree that gives us olive oil. Its primary active compound, oleuropein, is a polyphenol that has attracted genuine scientific interest for its potential effects on blood pressure, blood sugar, and oxidative stress markers. A 2021 meta-analysis of randomised trials found mean systolic blood pressure reductions of around 5 mmHg in adults with prehypertension or hypertension, though the evidence base is still maturing and large-scale trials are limited.

What is Olive Leaf Extract?

Olive leaf extract is produced by drying and concentrating the leaves of Olea europaea into a powder. The resulting dry extract is standardised — usually to a percentage of oleuropein, the molecule most researchers focus on. Oleuropein belongs to a class of compounds called secoiridoids, and it breaks down in the body into smaller metabolites including hydroxytyrosol, which is one of the more potent antioxidant compounds found in any plant food. When you see "olive leaf extract" on a supplement label in the UK, you are almost always looking at this dry extract powder form.

In terms of where it sits in human biology, oleuropein and its metabolites are thought to interact with several pathways simultaneously: they appear to influence nitric oxide signalling in blood vessel walls, modulate certain inflammatory markers, and act as free-radical scavengers. None of this is unique to olive leaf extract — many polyphenols do similar things — but the concentration of oleuropein in the leaf is substantially higher than in the fruit or oil, which is why the leaf has become the focus of supplementation research.

It is worth being clear about what olive leaf extract is not. It is not a pharmaceutical. It has no registered health claim under the EU Nutrition and Health Claims Register (which the UK retained post-Brexit). That does not mean the research is worthless — it means the evidence base, while genuinely interesting, has not yet met the regulatory threshold for approved claims. That honesty matters when deciding whether something deserves a place in a daily routine.

A note on limitations: Most published trials on olive leaf extract are short in duration (8–12 weeks), small in sample size, and heterogeneous in their choice of dose and oleuropein standardisation. The evidence discussed below should be read with those constraints in mind. Longer, larger, pre-registered trials in healthy adults are still largely absent from the literature.

Clinical Evidence

The most relevant human data on olive leaf extract concerns blood pressure. A systematic review and meta-analysis by Ismail et al. (2021) pooled data from randomised trials in adults with prehypertension and hypertension and found that olive leaf extract supplementation was associated with a mean reduction in systolic blood pressure of approximately 5 mmHg and diastolic blood pressure of around 3 mmHg compared to placebo. Those are modest numbers — comparable to the effect you might see from a meaningful dietary change — but they are consistent across the studies included. A separate meta-analysis by Álvares et al. (2024) covering cardiometabolic risk factors more broadly found similar directional signals, though the authors noted meaningful heterogeneity between trials, which limits how confidently the findings can be generalised.

A randomised, placebo-controlled trial by Stevens et al. (2021) examined cardiovascular health markers specifically. Participants receiving olive leaf extract showed some favourable shifts in lipid and inflammatory markers compared to placebo, though the trial was relatively small and the authors were appropriately cautious about the clinical significance of the findings. The direction of effect was consistent with the mechanistic picture — oleuropein metabolites may support healthy vascular function — though a single modest-sized RCT warrants careful interpretation rather than confident conclusions.

On blood sugar, a systematic review by Leach et al. (2025) specifically examined glycaemic control in adults with type 2 diabetes. The review found some evidence that olive leaf extract may modestly influence fasting glucose and insulin sensitivity, though the authors concluded that the quality of available evidence was low to moderate and that larger, better-designed trials are needed before firm conclusions can be drawn. A broader meta-analysis by Câmara et al. (2026) on the metabolic and inflammatory effects of oleuropein and olive leaf extract reached a similar conclusion: directionally promising, but the evidence base is not yet mature.

There is also a small but interesting body of work on antioxidant and anti-inflammatory activity. Allegretta et al. (2023) examined olive leaf extract as a novel antioxidant in the context of cystic fibrosis-related inflammation, finding that it may attenuate certain inflammatory markers in cell models. This is preclinical work rather than a human trial, so it sits lower in the evidence hierarchy — but it does help explain the mechanistic rationale for the human RCT findings. Separately, Toulabi et al. (2022) conducted a randomised double-blind study on olive leaf extract's effect on healing herpes simplex labialis (cold sores), finding faster resolution in the treatment group compared to placebo — an intriguing finding, though it was a single trial with a specific application.

Finally, a combined-extract trial by Wong et al. (2015) tested olive leaf alongside green coffee bean and beetroot extracts in a randomised, double-blind design and found that the combination may support healthy blood pressure in overweight adults. Because this was a multi-ingredient product, it is difficult to attribute the effect specifically to olive leaf extract — a limitation worth acknowledging. Across all of this, the honest summary is: the evidence is genuinely promising, particularly for blood pressure and cardiometabolic markers, but large-scale, long-duration RCTs in healthy adults are still largely absent.

Dosage: What Research Supports

Across the human trials reviewed here, doses of olive leaf extract (as dry extract powder) have typically ranged from 500 mg to 1,000 mg per day, taken as a single dose or split across two. The blood pressure trials that showed the clearest signals — including those pooled in the Ismail et al. (2021) meta-analysis — generally used doses in the 500–1,000 mg range. There is no EFSA-established dietary reference value for olive leaf extract, and the NHS does not currently publish guidance on supplementation doses, so clinical trial data is the most useful reference point available.

It is also worth noting that standardisation matters. A 500 mg capsule of olive leaf extract standardised to 20% oleuropein delivers approximately 100 mg of oleuropein per dose. Products with no stated oleuropein percentage may deliver considerably less of the active compound at the same nominal weight — something worth checking on any label. KōJō Daily Formula provides 500 mg of dry extract powder per serving, which sits at the lower end of the clinically studied range and is consistent with the doses used in several of the positive-signal trials.

How KōJō Uses Olive Leaf Extract

Olive leaf extract is ingredient number 6 of 42 actives in the KōJō Daily Formula. The dry extract powder form was chosen because it is the form used in the human trials — not a whole-leaf powder, not an oil, but a concentrated, standardised extract. The 500 mg dose reflects the lower bound of the clinically studied range: enough to be meaningful, not so much that it dominates the formulation at the expense of the other 41 ingredients. Within the formula, it sits alongside other polyphenol-rich compounds and antioxidant-active ingredients, which is consistent with how most of the positive trial data has been generated — olive leaf extract tends to be studied as part of a broader dietary approach rather than in isolation.

I am not going to tell you that 500 mg of olive leaf extract will dramatically shift your cardiovascular markers. The evidence does not support that claim, and I would rather be honest about what a single ingredient in a daily formula can realistically do. What I can say is that the mechanistic rationale is sound, the directional evidence from human trials is consistent, and the safety profile at this dose is well established.

Safety and Considerations

Olive leaf extract has a good safety record at the doses used in clinical trials. The most commonly reported side effects are mild and gastrointestinal in nature — nausea or loose stools, typically when taken on an empty stomach. Leach et al. (2025) reviewed adverse events across the trials they pooled and found no serious safety signals at doses up to 1,000 mg per day. That said, because olive leaf extract may influence blood pressure and blood glucose, there is a theoretical interaction risk with antihypertensive medications and diabetes drugs — the combination could potentially produce additive effects that push readings lower than intended.

Consult a healthcare professional before starting olive leaf extract if you are pregnant, breastfeeding, taking medication, or have an underlying condition. This is particularly relevant if you are on antihypertensives, blood thinners, or glucose-lowering medication. KōJō Daily Formula provides 500 mg of dry extract powder per serving — stay within the single-serving guidance. If you experience any gastrointestinal discomfort, taking the formula with food typically resolves it.

Frequently asked questions

This article is for informational purposes only and does not constitute medical advice. Consult your healthcare provider before starting any supplement regimen.