Why not? He's not going to report you to the police (if he does, you can sue him for violating your rights). I prefer patients tell me when they are using drugs. The worst he will do is counsel you about the side effects. You can tell him that you are taking a calculated risk, and right now for you the benefits outweigh the risks, and you want to check your LFT's to make sure that the risks aren't starting to outweigh the benefits.