If you shoot someone, regardless of the situation, you will have to deal with the legal consequences.
If you test positive for alcohol or pot, or meth or whatever, when you shoot someone, you'll be making some young prosecutor happy.
Always remember - "self-defense" is a defense to murder, manslaughter, or even assault with a deadly weapon. As such, the burden to prove self-defense falls squarely on you as the defendant. The prosecutor doesn't have to prove a single thing when you plead self-defense - in doing so, you've already made the prosecutor's case in chief. All the Prosecutor has to do is sit back and throw stones at your self defense claim. Pot, alcohol, meth, etc. - think of them as big, heavy, rocks moving at 600 fps right at you.