My husband was originally put on this medication when first diagnosed. His G.P. assumed that at age 40, he was dealing with type 2. It wasn't until he saw his current endo, that he was properly dx with type 1.
He of course had to change treatment plans, but he had no side effects whatsoever from the Metformin. (I can't remember how long exactly he was on it, but certainly long enough to have experienced some if there were any to be had)
Good luck, I hope that you will do well with this! Diet, exercise and oral meds are certainly preferrable to injections
Take care,
Scaredy Cat