My 16-month theanine self-experiment

> I’ve long found that tea makes me much less nervous than coffee, even with equal caffeine. Many people have suggested theanine as the explanation, but I’m skeptical. Most tea only has ~5 mg of theanine per cup, while when people supplement, they take 100-400 mg. Apparently grassy shade-grown Japanese teas are particularly high in theanine. And I do find those teas particularly calming. But they still only manage ~25 mg per cup

It's not uncommon for a substance to have different, even opposite effects at different doses. For example high dose melatonin can keep you up, and stress you out, whereas in most people you only need up to 1 mg to promote sleep.

https://en.wikipedia.org/wiki/Hormesis

I would also look at other ingredients in teas as a knock on effect vs straight supplement extracts. Sometimes the extract as a supplement isn’t the same once separated from the rest of the plant it’s found.