https://www.emjreviews.com/neurology/news/artificial-sweetener-erythritol-linked-to-brain-vascular-cell-dysfunction/

Source that actually names the thing in its title.

Unfortunately it's of course barely readable for laypeople. So is there a safe upper limit? Like if I put a teaspoon of it in my cup of coffee, am I destroying my brain?

Cells were treated with 6 mM erythritol, replicating the concentration found in a typical serving of an artificially sweetened drink, for three hours.

What's "mM"?