just look in pub med for any medication and the term liver damage
or enymes and buches of studies suggest damage
is being done.
here's but one of the many..
Liver and kidney toxicity in chronic use of opioids: an experimental long term treatment model.Atici S, Cinel I, Cinel L, Doruk N, Eskandari G, Oral U.
Department of Anesthesiology and Reanimation, Mersin University, School of Medicine, Mersin, Turkey.