Hi Debbie, as I understand it, they perform different roles: Metformin is to help combat Insulin Resistance (IR) so that the body can make best use of the insulin that you do have, and it also helps to reduce the amount of glucose released from the liver's stores of glycogen. Injected insulin is used to overcome any shortfall in your own secreted insulin in its task of reducing Blood Glucose levels. So they have complimentary roles, but if the Metformin does not agree with you I am sure there may be alternatives to discuss with your HCPs.