no idea what effect this has on muscle building.
but there are plenty of pain killers out there that are not pressed with acetaminophen/ibuprofen. unfortunately they are schedules differently because they are easier to abuse this way (ie. oxycodone.)
if you suffer from moderate or chronic pain you should consult your doctor as to what options you may have.
im going to go back in for a script cause my back is killing me. ill letcha know what i find out.