[thesheepdog]

If your peripheral nerve receptors (nerves controlling your extremity muscles) are being blocked by a chemical (drug), another manipulative reaction (tazer) will not work, unless the second reaction is stronger than the first.
Some drugs will completely block all receptors in the nervous system, and the user will not feel pain and/or be affected by other reactions (tazer).

Speaking in plain english, view drugs as insulation on your body that prevents conduction of the tazer; If the nerves are protected (coated if you will) by the drugs, then a nervous system response to the tazer will not occur, until the drugs wear off, and/or the CNS is not damaged by the drugs (tolerance)

I am an ALS medic and know a lot about drugs and their affects on the body.