It's hard to sure. I imagine using it too many times would at the very least lock you into a bad ending.
I think the most likely consequence is that using the tadpole too much costs you some amount of time needed to find an alternative option to taking Raphael's deal. There is probably at least one way to avoid taking the deal with Raphael, but it'll likely be difficult to find and happen very late in the game. My guess is that if your tadpole infection has advanced to a certain stage, it locks you out of some options which are less costly. My guess is that the more you use it, the more costly the remaining tadpole-be-gone options are until perhaps at one point, you get pulled into a cutscene where Raphael tells you your time is up, and it's take his terms or die, and if you refuse, he shrugs and you get a game over.
