What side effects cause people taking Metformin to discontinue it? I'm taking, but haven't noticed any, but... you don't notice your baseline, I suppose!
For non-diabetics hoping Metformin will bring health benefits, the subtle side effects like reducing adaptive responses to exercise ( https://pmc.ncbi.nlm.nih.gov/articles/PMC6351883/ ) and other small negatives aren’t usually advertised by the anti-aging influencers who only talk about the lifespan studies (in mice)
From the perspective of "Should I be worried about side effects from taking this drug / should I not take this because it might give me this effect", I think this falls under "be aware of symptoms and stop or weigh the costs if you get it, but you're probably fine".