I don't think you should take the drug test. His idea that you are taking drugs when you aren't taking them at all is incredibly bizarre, imo, assuming that you don't take anything at all. If you do some kind of drug occasionally, it might be a more reasonable fear on his part. If you take nothing, ever, then it's just a really strange thing for him to say.

The counselor sounds like a great idea. I don't think you will be able to reason your way out of this. His accusation is not based in reality.