Codeine is not toxic to the liver. It stresses the liver in some ways simply due to the fact that the liver must "work" to metabolize the drug, but it is in no way directly harmful to the body. As the above poster said, the real danger with Opioids lies in acute overdose through respiratory depression. Treatment with Opioids in their pure form, be it Morphine, Diamorphine, Codeine or what have you is sustainable long-term with the primary health complication being constipation. Don't get me wrong, constipation can actually cause serious health problems or even death, but it's generally treated pretty easily with over the counter laxatives.
It's easy to get confused regarding the APAP/NSAID combination products. Codeine in the United States is almost always paired with an NSAID of some kind, generally APAP unless the patient is allergic. People in the past and currently have slowly killed themselves through excessive use of these combination products without removing the APAP. Liver damage, failure and cancer can all occur pretty easily as APAP is actually quite nasty for the body. You can safely assume that if someone is taking Codeine, they're taking it in the form of a Tylenol 1,2,3,4 or whatever. The general population is not aware of things like Cold Water Extraction unfortunately. My Pharmacist didn't even have any idea about the process.
