If I remember correctly, agave nectar is classified as a
Class 3 or 4 poison.
Mildly dangerous, but not toxicly so unless you consume a lot of it or are sensitive. If you have IBS, you'd want to avoid it.
Still enough that I rarely if ever buy it anymore.
Most "sugar substitutes" are at least as bad for you as sugar. Some are much worse. You are much better off sticking to
fruit and sweet vegetables as the sweet in your diet.