Dose makes the poison, some people are capable of handling more, and some less.
Tea, among other things, has caffeine in it, and enough caffeine will kill you, but other than in pill form, you’ll likely not manage to get to the threshold because you’ll start vomiting way earlier.
It’s possible that there are other compounds harmful at high concentration. And of course, it’s not unthinkable that some of his pills were contaminated with something more dangerous.
But the dosage alone in some cases may explain enough of the damage.
Caffeine toxicity can happen much earlier, but it's mostly concerning in combination with other substances. Caff on its own ... it's really, really hard to get to a dangerous dose inadvertently.
If the substance is pure, and the dosage is correctly labeled. Neither of which is especially common for nutritional supplements.
The key to this article is the line, "catechin doses at or above 800mg may pose health concerns." Pop over to amazon and look at one of the top results for green tea extract: https://www.amazon.com/NOW-Green-Tea-Extract-Capsules/dp/B00... A single pill is 160mg.
> What is it about green tea supplements that might cause harm at certain doses to some people? Scientists do not know for certain. Because green tea has been drunk for thousands of years, supplements consisting of its concentrated form are regulated in the US and Europe as foods, not medicines. That means that specific safety testing has not been required, so the scientific picture of how green tea supplements might affect our health is incomplete.