metformin isn't going to induce a bleed.

metformin is the drug they give to PCOS people to control the insulin resistance. Doing that can help the ovaries function more normally and restore regular periods.

I suspect that the drug they use to induce a bleed is a type of birth control pill, and stopping it causes a withdrawal bleed. I haven't researched that at all, so it is just guess work.

BW