Benefits
Antiviral activity against a respiratory virus in lab cells only (maker-funded)
In a maker-funded in vitro study, dog kidney cells pretreated with Isenolic and then infected with human influenza A showed less activity of neuraminidase, a viral enzyme the virus uses to spread, with the 8 percent elenolic acid version reaching 64 percent inhibition at 100 µg/ml. These are cell-dish results, not effects in people.
Narrow gap between antiviral effect and cell toxicity in the lab
In the same in vitro study, the 8 percent version needed 65.5 µg/ml to halve viral enzyme activity, while 149.7 µg/ml halved the viability of uninfected cells, a selectivity index of only 2.3 (1.3 for the 4 percent version). At 100 µg/ml it kept 72.9 percent of heavily infected cells viable versus 29.6 percent without it.
Upper respiratory sick days: one small trial of a different olive leaf extract
In a 9-week randomized trial in 32 high school athletes, a different olive leaf extract providing 100 mg oleuropein a day did not change how many got an upper respiratory illness, but those who did had about 28 percent fewer sick days. Its elenolic acid content was not reported, and Isenolic has no published human results.
Registered cold and flu trial of Isenolic stopped early without reported results
A maker-funded, placebo-controlled trial in Australia (ACTRN12619001722189) gave healthy adults 150 mg twice daily from the first cold or flu symptoms to test symptom duration. It enrolled 135 of a planned 200 people, stopped early over recruitment problems and has posted or published no results, so it offers no evidence either way.
Antioxidant activity of olive leaf extracts in cell studies only
Two olive leaf extracts protected human cells in culture from oxidative damage and raised antioxidant enzymes in a lab study. That work did not test Isenolic or elenolic acid, and no study cited here has measured antioxidant or immune markers in people taking Isenolic.
Mechanism of action
Viral neuraminidase activity (lab marker)
Neuraminidase is an influenza surface enzyme that frees new virus particles from infected cells. In the maker's cell study, pretreating cells with Isenolic lowered neuraminidase activity in the culture fluid, which the authors used as a marker of virus production. No study cited here has measured whether elenolic acid reaches the airways in active form after swallowing.
Older elenolate antiviral work used direct contact, not capsules
Calcium elenolate, a salt of elenolic acid, was described in older research as virucidal, meaning it inactivates virus on contact. In a hamster study it lowered influenza virus in nasal washes when given as nose drops near the time of infection. That route says nothing about swallowing an olive leaf extract.
Olive leaf compounds in cell studies
Olive leaf compounds, mainly oleuropein, have shown antiviral and antioxidant activity in cultured cells, for example slowing herpes simplex virus replication in a human cell line. These lab findings involve a different marker compound than Isenolic's elenolic acid standard and do not show what happens in people who swallow an extract.
Clinical trials
Laboratory cell-culture study funded by the manufacturer, Pharmactive Biotech Products, which supplied the samples and employed five of the six authors, with Spanish public research grants to two of them; a university group ran the chemical analysis. Cells were pretreated with 4 percent or 8 percent elenolic acid versions of Isenolic for 1 hour, washed, then infected with human influenza A (H3N2). A licensed antiviral drug served as the positive control. (Salamanca et al. 2021, Antivir Chem Chemother)
No people. Sialic acid overexpressing Madin-Darby canine kidney (MDCK-SIAT1) cells.
Viral neuraminidase activity in the culture fluid, used as a marker of virus production, fell as extract concentration rose: the 8 percent version reached 64 percent inhibition at 100 µg/ml versus 28.6 percent for the 4 percent version (whose maximum was 44.1 percent at 150 µg/ml). Concentrations halving enzyme activity were 65.5 and 171.4 µg/ml, but concentrations halving the viability of uninfected cells were only 149.7 and 218.2 µg/ml, giving low selectivity indexes of 2.3 and 1.3. Pretreatment with the 8 percent version kept 72.9 percent of heavily infected cells viable versus 29.6 percent without it. The control drug gave stronger results on both measures. These in vitro results do not show any effect of swallowing the extract.
Randomized, placebo-controlled, blinded trial funded by Pharmactive and run in Queensland, Australia. Participants took one 150 mg Isenolic capsule twice daily, or an identical maltodextrin placebo, from the first day of cold or flu symptoms, with a 2-week supply per episode and up to 4 months of participation. (ANZCTR registration ACTRN12619001722189, 2019)
Generally healthy adults aged 18 to 65. Target 200; 135 enrolled between July 2020 and January 2022.
Stopped early because of recruitment difficulties. The main outcome was change in cold or flu duration on the WURSS-24 symptom questionnaire; secondary outcomes were symptom severity, stomach tolerance and missed work days. Data collection ended in May 2022, but as of this audit no results have been posted to the registry or published in PubMed, so the trial provides no evidence of benefit or of no benefit.
Class evidence, not Isenolic. Randomized, double-blind, placebo-controlled 9-week trial of an olive leaf extract given as one tablet a day equivalent to 20 g of leaf and containing 100 mg oleuropein, with no elenolic acid content reported. Funded by a University of Auckland seed grant; authors declared no conflicts. (Somerville et al. 2019, Nutrients)
32 high school students on elite school sports teams, during their competitive season.
No difference in how many athletes got an upper respiratory illness (odds ratio 1.02, 95% CI 0.21 to 4.44). Those who got sick had about 28 percent fewer sick days on the extract (odds ratio 0.72, 95% CI 0.56 to 0.93, p = 0.02). One small trial of a differently standardized extract; it does not show what Isenolic does.