Green tea has gained tremendous popularity as an all-around health elixir, touted to burn fat and prevent an array of illnesses, including cancer and heart disease.

With enticing names such as Green Tea Triple Fat Burner and Green Tea Slim, many people are drawn to supplements of green tea for weight loss. Consumers spent about $140 million on them in 2015, according to the latest data available from the Nutrition Business Journal. Meanwhile, tea, including green tea—made by steeping tea leaves or blending green tea powder in hot water—is the second most popular beverage worldwide, surpassed only by water.

But is there scientific substance behind the claims that green tea is good for weight loss or overall health? We reviewed the research and spoke to experts to find out.

Will Green Tea Help With Weight Loss?

It’s true that green tea can raise your metabolic rate, so you burn more calories, says David Nieman, Dr.PH., director of the human performance laboratory at Appalachian State University in Boone, N.C. Nieman, who has studied green tea extensively, says this effect is probably due to a combination of its caffeine and catechins—antioxidants that are plentiful in green tea and present in smaller amounts in some fruits, dark chocolate, and red wine.

But the effect is likely to lead to little, if any, change on the scale. “People think if you drink a few cups of green tea, you’ll see the fat melt away,” Nieman says. “That’s just not going to happen.”

Even at large doses, the effect of green tea for weight loss is minimal. For example, in a study published in the journal Clinical Nutrition in 2016, overweight women took either a daily dose of about 1,350 mg of green tea extract in supplement form (the equivalent of roughly 15 cups of green tea) or a placebo for 12 weeks. Though the green tea group dropped an average of 2.4 pounds, the women taking the placebo lost 4.4 pounds.

What’s more, experts warn against taking the large amounts used in studies like this one—and recommended on many supplement labels. There have been reports of serious liver damage in people who used green tea supplements.

And one study published in 2017 in the journal Cancer Prevention Research found that postmenopausal women who’d taken green tea extract twice a day for a year as part of a breast cancer clinical trial had elevated liver enzymes—a sign of potential liver damage often seen in people who abuse alcohol. 

“This level of intake may well border on the toxic range,” says Jay H. Hoofnagle, M.D., director of the Liver Disease Research Branch at the National Institutes of Health. The potential risk of liver damage is one reason green tea extract is included on CR’s list of 15 supplements you should never take.

Still, when it comes to losing weight, working a few cups of brewed green tea into your diet isn’t necessarily a bad idea. “Like coffee, green tea may give you a mild boost, and if you don’t add sugar, it has no calories,” notes Consumer Reports’ chief medical adviser, Marvin M. Lipman, M.D. “So drinking it in place of sugary drinks such as soda can help you cut calories.” 

But don’t guzzle gallons of it. It’s unclear exactly how much green tea is safe to drink, partially because concentrations of catechins can vary widely from cup to cup. A few cups per day is probably safe, Lipman says. 

Does Green Tea Prevent Cancer?

Catechins are also credited for green tea’s cancer-fighting potential. These antioxidants have the ability to block the action of molecules called free radicals, which can cause changes in healthy cells that sometimes lead to cancer. But there’s no solid proof yet that the catechins in green tea help to prevent cancer in humans, despite some promising studies in test tubes and animals.

In 2009 the Cochrane Library published a review of 51 studies that included a total of more than 1.6 million participants. Each study investigated whether consuming green tea reduced the risk of developing specific types of cancer, including those of the breast, colon, oral cavity, liver, pancreas, and prostate.

The results were conflicting, says lead author Katja Boehm, Ph.D., a health psychologist at Private University Witten/Herdecke in Germany. After scrutinizing the data, Boehm says, the evidence of a benefit wasn’t strong enough to recommend using green tea to protect against cancer.

Can Green Tea Prevent Heart Disease?

Some data suggests that green tea can reduce the risk of cardiovascular disease—a narrowing of the arteries that can lead to heart attack, chest pains, or stroke. 

For example, in a study of more than 40,500 adults, researchers in Japan found that those who consumed five or more cups of green tea per day were 26 percent less likely to die of cardiovascular disease over an 11-year period than those who drank just one cup per day.

Similarly, a study of 76,979 people published in the Journal of Epidemiology and Community Health in 2011 found that women who drank one to six cups of green tea per day had a reduced risk of dying of cardiovascular disease (over an average of 13 years) compared with those drank none.
How might green tea protect the heart? Experts say it may reduce high cholesterol levels and high blood pressure, which are important factors in cardiovascular disease.

“These findings are intriguing, and there’s no harm in drinking reasonable amounts of green tea,” Lipman says. “But it’s no miracle cure.”

To reduce your risk of diseases such as cancer and heart disease (as well as keep your weight in check), he says, you need to eat a healthy diet that includes plenty of fruit, vegetables, and whole grains. You should also exercise and avoid smoking.

“Green tea alone isn’t going to atone for bad habits,” Lipman says, “and you certainly shouldn’t rely on it as the key to good health.”