I've seen people make stuff to squirt in Bearded Dragons' mouths and they crushed TUMS in it to help with their stomachs or something like that. Honestly, I couldn't tell you if it is safe or not, but I've seen people use it with Beardies.

Why would you be feeding it in the first place? And I highly doubt the lizard would eat a TUMS if it doesn't look like something in its normal diet.