Here's what you need to know.
Health Canada is issuing warnings on labels of green-tea extract products after 17-year-old Madeline Papineau, of Ontario, reportedly took the extract and developed serious organ damage, CBC News reports. Per CBC News, doctors were initially stumped as to what caused Madeline's kidney and liver damage, until her younger sister mentioned she'd been taking a diet supplement that contained the ingredient.
Health Canada will strengthen warnings on labels by including the language: “Rare, unpredictable cases of liver injury associated with green tea extract-containing products have been reported (in Canada and internationally).”
A federal review in Canada concluded that while the majority of people who take green-tea extract “in any form, do so without harm,” they also found that “there may be a link between the use of green tea extract and a risk of rare and unpredictable liver injury.”
The warnings are nothing new—including in the U.S. In 2014, The American College of Gastroenterology released guidelines on drugs and herbal supplements that can cause liver injury. Topping the list of herbals? You guessed it: green-tea extract. Some pills, they note in the press release, can contain more than 700 milligrams (mg) of catechins (the active compound in green tea), whereas a cup of green tea contains 50 to 150 mg, and people tend to take these pills multiple times a day.
"In animal studies, when some strains of mice are given high doses of EGCG (the active catechin in green tea), they develop acute liver injury that looks like Tylenol toxicity," explains Herbert Lloyd Bonkovsky, M.D., gastroenterology professor at Wake Forest Baptist Health. He notes that some people—because of factors like genetics—may be more prone to liver damage than others. "Fasting also increases the absorption of catechins, meaning there may be a higher risk of injury for people who are trying to lose weight," he says.
Bonkovsky also notes that while drinking green tea is almost always safe, there have been some reports of people developing liver injury after consuming large amounts, like eight or 10 cups a day.
Another study in 2017 in the journal Hepatology also found that anabolic steroids and green-tea extract were two of the most common supplements to cause liver damage.
Aside from that, there are many unknowns when you take supplements. “Supplements are not a regulated industry. There are no standards or guidelines to how they should be produced, testing of ingredients, or how/where they can be sold. It's not safe to assume all supplements claiming to contain a certain ingredient are universally safe,” says Sea Girt, New Jersey-based registered dietitian nutritionist Mandy Enright, R.D.N. She also notes that supplements are often sold in stores where employees aren’t educated about the product—or can be easily bought online. You may not always be aware of the side effects and risks of what you’re taking.
“When in doubt, aim to get the ingredient or nutrient from its natural food source, such as drinking green tea versus taking a questionable pill form,” she says.