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, these pens are not likely to be readily available for animal use in the near future. Insulin injections are given under the skin and do not hurt.