I know that the thickeners and sweeteners in cough syrup very well might be harsh on your liver, but are the gel caps the same? Is the only way to get around liver toxicity to extract?
I changed the title just to make the topic more clear and for future search purposes.
As far as your question is concerned, I'm not aware of any inactive ingredients in DXM-only syrups OR pills that are hepatotoxic. If the preparation contains other ACTIVE ingredients such as acetaminophen then this is a very different story. I don't think you have to worry about hepatotoxicity of sweeteners or fillers.