A Texas man needed a liver transplant after taking green tea extract, and his case isn't the first of its kind. Green tea supplements (but not actual green tea) have been linked to liver damage in the past, too.
To be clear, liver damage from supplements is rare, and there are only a handful of known or strongly suspected cases. The Texas man, Jim McCants, says his doctors concluded the green tea supplements were probably at fault after they first considered alcohol (he barely drinks) and prescription drugs (he wasn't taking any). It's possible something else caused his liver damage, but it's also possible that others have been harmed and never found out why.
The US National Institutes of Health, in its LiverTox database, scores green tea extract as a "well established cause of clinically apparent liver injury." They also note that green tea extract is one of many ingredients in Hydroxycut, a weight-loss supplement known to cause liver injury.
Supplement-related liver injury is on the rise, according to a 2016 study published in Hepatology, and green tea extract is a common ingredient in many of the supplements linked to liver injury. (Anabolic steroids are another. Don't do steroids, kids.)
What You Can Do
If you drink green tea, feel free to keep drinking it. The people who have gotten liver damage were taking concentrated supplements, not sipping tea.
Unfortunately, there isn't a good way to be sure that your supplements are safe, even though liver damage is rare. The chemicals in green tea that seem to cause the damage are catechins, the exact same chemicals that have been linked with weight loss and heart health benefits — in other words, the reason people take the pills in the first place.
Supplements aren't required to be tested for their safety, so taking herbs is always kind of a crapshoot. The European Food Safety Authority issued a warning that people should avoid taking more than 800mg per day of green tea catechins, which might be a good rule of thumb to follow.