Tolerance?

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Can your body build a tolerance to metformin, I recently was put on metformin to bring my periods back and ovulate , after 3 weeks I started my period, so it's working! My husband is deployed and doesn't get back till April , I guess what I'm worried about it if I'd build a tolerance up for it in these next 5 months and it stop making me have a period or stop working for me ,is that possible ?