Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health.

Emily Dashiell, ND, is a licensed naturopathic doctor who has worked in group and private practice settings over the last 15 years. She is in private practice in Santa Monica, California.

Olive leaf extract has long been used in traditional medicine. It comes from the leaves of the olive tree (Olea europaea) and has many health benefits. 

The main component of olive leaf extract is oleuropein . Medicinally, it acts as an:

This article looks at the possible health benefits of olive leaf extract, along with side effects, dosage and preparation, and what to look for when buying it.

Medical research on olive leaf extract is in its early stages. Some preliminary studies suggest it may help treat:

So far, research is strongest for its use in:

Olive leaf extract may aid in diabetes control. In one study, 79 adults with type 2 diabetes took either olive leaf extract or a placebo every day for 14 weeks.

In the end, the olive leaf extract group had significantly more improvement in blood sugar levels than the control group.

While this study was small, it supports findings from earlier animal studies. Still, more research is needed.

Olive leaf extract shows promise for treating hypertension. In a small study comparing olive leaf extract to placebo, researchers found olive leaf lowered:

Again, this was a small study that built on previous research. It may lead to larger studies that offer more complete information about safety and effectiveness.

Olive leaf extract has antiviral properties. It's used in holistic medicine to treat certain viruses.

Lab tests show olive leaf extract can fight herpes, mononucleosis, and rotavirus. It may also be useful against influenza and HIV.

This research has been limited to cell cultures. The benefits remain to be proven in human studies. However, anecdotal evidence suggests it can effectively treat cold sores.  

Olive leave extract supplements come in capsules, softgels, and tinctures. The standard dose ranges between 500 milligrams (mg) and 1,000 mg daily.

Most supplement labels recommend splitting the dose. That gives you between 250 mg and 500 mg. It should be taken two to four times a day with food.

Always follow the instructions on the label when taking supplements. Or talk to your healthcare provider about the dosage that's right for you.

Olive leaf extract is an antioxidant, anti-inflammatory, and antimicrobial. It's claimed to help manage many conditions, but research best supports just a few: diabetes, high blood pressure, and viral illnesses.

There are no standard guidelines on dosages. Most supplement labels recommend between 500 mg and 1,000 mg, sometimes divided into up to four doses, per day.

Little is known about the safety of regularly taking olive leaf extract. But there's some concern it may trigger mild side effects like stomach pain and headache.

Some people may develop an allergy to olive leaf extract. The pollen from the olive leaf can trigger severe respiratory allergic reactions in people allergic to plants in the Oleaceae family, including:

Olive leaf extract may interact with certain medicines. Unless your healthcare provider approves it, don't take it if you're on:

The use of antioxidants during chemotherapy is controversial. Some oncologists (cancer specialists) believe it could prevent drugs from killing cancer cells. But some research suggests it may make chemotherapy drugs more effective while also curbing their side effects.

Supplements aren't tested and regulated like drugs. Sometimes, the dosages and ingredients on the label don't match what's in the bottle.

When buying supplements, look for products that have been certified by one of the following:

These are independent labs that evaluate supplements for purity. They help ensure you're getting what the label says. They don't guarantee safety and effectiveness, however.

Olive leaf extract may help treat hypertension, diabetes, cold sores, and more, but science isn't settled. Research continues to look into how the medicinal properties of olive leaf extract may be used.

Be sure to talk with your healthcare provider before taking olive leaf extract or any supplement. Watch for side effects and drug interactions when you add olive leaf extract to your diet.

If you're allergic to related plants—including forsythia, ash, and olive trees—you may be allergic to olive leaf extract, as well.

Research isn't yet certain enough to recommend olive leaf extract for any condition. Self-treating a condition and avoiding or delaying standard medical care may have serious consequences.

If you're considering olive leaf extract for any health purpose, talk to your healthcare provider first.

It might. In animal studies, olive leaf extract has been shown to prevent obesity. Researchers think it works by regulating the expression of genes that affect weight gain. It may also be an appetite suppressant. These results haven't been confirmed in human trials.

Supplement makers say to store olive leaf extract in a cool, dark place, such as a cabinet or the refrigerator.

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Memorial Sloan Kettering Cancer Center. Olive leaf.

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