Olive leaf contains a substance called oleuropein, which breaks down in the body to another substance called enolinate. On websites that promote olive leaf extracts, it is stated that enolinate kills harmful bacteria, viruses, and fungi in the body, but at the same time nurtures microbes that are good for health. This remarkable claim however, has no meaningful scientific evidence.
It is true that oleuropein, enolinate, and other olive leaf constituents or their breakdown products can kill microbes in test-tube studies.1-11 However, it is a long way from test-tube studies to evidence of efficacy in humans. Only double-blind, placebo-controlled studies can prove a treatment effective.
In addition to the claim that olive leaf can kill harmful substances in the body, proponents also advocate its use to reduce blood pressure. Test-tube and animal studies have produced some positive preliminary findings.13-16 And a small study did find evidence to support this, but there were flaws in its design.12 A more recent, larger study offers more promising news, though. Two hundred and thirty-two people (aged 25-60) with high blood pressure were randomized to receive olive leave extract (500 mg, twice daily) or a commonly used anti-hypertensive medication called captopril (12.5 mg, twice daily) for a total of 8 weeks. Both treatment groups experienced similar reductions in blood pressure levels.20
Olive leaf has also been studied as a potential treatment for other conditions. For example, animal studies weakly suggest that olive leaf might help control blood sugar levels in diabetes17-19 and reduce symptoms of gout.17
Olive leaf has not undergone comprehensive safety testing. However, based on the limited evidence available, it does not appear to commonly cause much more in the way of immediate side effects than occasional digestive distress. Safety in young children, pregnant or nursing women, or people with severe liver or kidney disease has not been established.
Aziz NH, Farag SE, Mousa LA, Abo-Zaid MA. Comparative antibacterial and antifungal effects of some phenolic compounds. Microbios. 1998;93:43–54.
Bisignano G, Tomaino A, Lo Cascio R, Crisafi G, Uccella N, Saija A. On the in-vitro antimicrobial activity of oleuropein and hydroxytyrosol. J Pharm Pharmacol. 1999;51:971–4.
Elliott GA, Buthala DA, DeYoung EN. Preliminary safety studies with calcium elenolate, an antiviral agent. Antimicrobial Agents Chemother. 1969;9:173–6.
Fleming HP, Walter WM Jr, Etchells JL. Antimicrobial properties of oleuropein and products of its hydrolysis from green olives. Appl Microbiol. 1973;26:777–82.
Heinze JE, Hale AH, Carl PL. Specificity of the antiviral agent calcium elenolate. Antimicrob Agents Chemother. 1975;8:421–5.
Hirschman SZ. Inactivation of DNA polymerases of murine leukaemia viruses by calcium elenolate. Nat New Biol. 1972;238:277–9.
Juven B, Henis Y, Jacoby B. Studies on the mechanism of the antimicrobial action of oleuropein. J Appl Bacteriol. 1972;35:559–67.
Lee-Huang S, Zhang L, Huang PL, Chang YT, Huang PL. Anti-HIV activity of olive leaf extract (OLE) and modulation of host cell gene expression by HIV-1 infection and OLE treatment. Biochem Biophys Res Commun. 2003;307:1029–37.
Renis HE. Inactivation of myxoviruses by calcium elenolate. Antimicrob Agents Chemother. 1975;8:194–9.
Renis HE. In vitro antiviral activity of calcium elenolate. Antimicrobial Agents Chemother. 1969;9:167–72.
Walter WM Jr, Fleming HP, Etchells JL. Preparation of antimicrobial compounds by hydrolysis of oleuropein from green olives. Appl Microbiol. 1973;26:773–6.
Cherif S, Rahal N, Haouala M, et al. A clinical trial of a titrated Olea extract in the treatment of essential arterial hypertension. J Pharm Belg. 1996;51:69–71.
Fehri B, Aiache JM, Memmi A, Korbi S, Yacoubi MT, Mrad S, Lamaison JL. Hypotension, hypoglycemia and hypouricemia recorded after repeated administration of aqueous leaf extract of Olea europaea L. J Pharm Belg. 1994;49:101–8.
Khayyal MT, el-Ghazaly MA, Abdallah DM, Nassar NN, Okpanyi SN, Kreuter MH. Blood pressure lowering effect of an olive leaf extract ( Olea europaea) in L-NAME induced hypertension in rats. Arzneimittelforschung. 2002;52:797–802.
Ribeiro Rde A, Fiuza de Melo MM, De Barros F, Gomes C, Trolin G. Acute antihypertensive effect in conscious rats produced by some medicinal plants used in the state of Sao Paulo. J Ethnopharmacol. 1986;15:261–9.
Zarzuelo A, Duarte J, Jimenez J, Gonzalez M, Utrilla MP. Vasodilator effect of olive leaf. Planta Med. 1991;57:417–9.
Fehri B, Aiache JM, Memmi A, et al. Hypotension, hypoglycemia and hypouricemia recorded after repeated administration of aqueous leaf extract of Olea europaea L [in French]. J Pharm Belg. 199449:101–8.
Gonzalez M, Zarzuelo A, Gamez MJ, Utrilla MP, Jimenez J, Osuna I. Hypoglycemic activity of olive leaf. PlantaMed. 1992;58:513–5.
Onderoglu S, Sozer S, Erbil KM, Ortac R, Lermioglu F. The evaluation of long-term effects of cinnamon bark and olive leaf on toxicity induced by streptozotocin administration to rats. J Pharm Pharmacol. 1999;51:1305–12.
Susalit E, Agus N, Effendi I, et al. Olive (Olea europaea) leaf extract effective in patients with stage-1 hypertension: comparison with Captopril. Phytomedicine. 2011;18(4):251-258.
Last reviewed December 2015 by EBSCO CAM Review Board
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.