It's pretty mild compared to A, with a large gap between the UL and getting sick.

Healthy adults need a few months on a dose two orders of magnitude higher than the typical recommendation to see overt toxicity. All known cases of toxicity stem from people going ten times the UL.

Still, don't handle this like a water soluble vitamin. Never think about bulk powders, since the IU-to-weight conversion ratio is crazy potent.