To put it in a different way, Insulin
is the most important substance or chemical produced in the body. Every organ system in body need Insulin for its function. It Insulin is deficient, it causes lots of problem which are complications of diabetes.
Insulin is usually needed in the later stages of Type 2 diabetes, when self Insulin production decreases and tablets alone cannot control the sugars.
In Type 1 diabetes
, Insulin is needed from the very first day, as the production suddenly stops.