My mom takes Zoloft & Mucinex DM, and recently has complaints of an upset stomach. Anyone have any experience with contraindications?

Mucinex DM has some powerful side effects, and you can tell this by the fact that it is being used OFF LABEL by people with "Fibromyalgia". Anything that people believe works for that is having some powerful action/reaction. It is apparently the Guaifenesin in it that can be problematic. I would look up Mucinex DM and Fibromyalgia on your search engine, also guaifenesin side effects. My partner had a lot of problems with his chronic GERD when he was taking Mucinex DM; I would say also that he actually developed quite a racking cough, when cough is what it is meant often to help. So I wouldn't be surprised if there is some reaction/interaction going on here. If problems began with the introduction of this medication I would stop it and see if that helps. Many people think over the counter stuff is pretty benign and it is sometimes anything but.