In summary, insulin is not reliable enough to be recommended if subcutaneous injection is the only available method of administration.
The RPA Test for Insulin
Insulin scores poorly at 60%, having a questionable reputation in the major indices of reliability and peacefulness. Availability varies. It is readily available for diabetics, and in for these people there are no legal issues. Insulin is difficult to prepare, administer (it must be given by injection) and to store (refrigeration is required).