Dad (63) has htn on oat. experiencing stomach burn, heartburn, very poor appetite & weight loss. smoker & regular drinker. not fond of doctor's visits?

What is OAT?: I cannot find this acronym in association with treatments for hypertension, so I cannot answer your question. It sounds like you are more concerned with your dad's health than he is, and that will make it unlikely that you can help. Without a medical evaluation of his symptoms, which are very likely related to, if not caused by, excessive drinking and smoking, hard to say. Cut down or stop both!!