He's not taking them separately but in a concoction, which is basically an anti-psychotic. He's showing a lot of the signs of classic thought disorders or psychosis. Whether this is from withdraw or trying to counteract whatever drug soup they had him on in the looney-bin, who knows? Yet.
Look at the way Peter reacts towards Walter when he gets flustered or eccentric and starts changing the subject or using his hands to think or goes off on separate tangents-- Peter knows he's a borderline psychotic, so he puts up with it, even if he berates him or becomes agitated.
As far as him concocting these drugs, I haven't really given it a second thought as he managed to whip up some homemade LSD within a few hours during the first episode. I'm assuming the FBI lab assistant can pretty much get clearance for whatever she needs for him.