How and when you give Slippery Elm depends on what you're using it for– upset, reflux, megaesophagus...
If a dog has a megaesophagus, give it a half-hour/hour before eating, so it coats their throat.
For a dog experiencing reflux, give it a half-hour/hour before they eat, so it coats their throat. Add warm water or bone broth (enough to make a thick slurry) and see how they do. If that doesn't work, then Dr. Bessent would recommend giving it after eating or between meals to soothe the stomach.
For a dog with digestive upset, Dr. Bessent suggests adding slippery elm to the meal to begin and then adjust if that doesn't seem to be effective by giving it after eating or between meals to soothe the stomach.
** Be sure to space slippery elm with any other medications or herbs you're giving your four-legger. The herb is such an effective mucilage that it can delay absorption. **