Some humans have a type of diabetes that can be controlled by a change in diet. Dogs do not get this type of diabetes and always require insulin injections. Insulin is a protein and (as with any other protein), can be digested. If insulin were given as a tablet, the tablets would be digested by the acid in the stomach and the insulin would have no effect. Special 'pens' (which inject insulin through the skin without the use of a needle) have been developed for use in diabetic people. However, dogs have a much thicker skin than humans and these pens are not likely to be readily available for animal use in the near future. The normal injections are given under the skin and do not hurt. A good tip is to feed your dog after administering the injection. Dogs quickly learn that once they have had their injection they get their food and so are happy to stand still for the jab.