Insulin is prescribed when investigations suggest that the pancreas is unlikely to be able to produce enough insulin and/or diet and antidiabetic drugs are not working.
Most types of insulin are extracted from pigs, although newer types are obtained from humans. The latter are proving to be more effective but also have more side effects. Specialists will prefer certain types and diabetics requiring insulin should follow their advice. I have never seen a case of insulin-dependent diabetes improved to the point that insulin is not required. Alternative therapies may reduce the daily injectable requirement but under no circumstances should insulin injections be stopped without your doctor’s approval.