At what dosage would it help someone who is overweight by 50lbs to loose weight, given a good diet and cardio/lifting isn't making it happen?
I would really advocate checking morning blood sugars to see if your weight gain is likely attributable to increasing insulin resistance. I would say, if you are in the 90's or above, then you are likely on the resistant end of the spectrum. Above 100 and for sure you need to consider Metformin and low carb diet.
I lost 40 lbs by going low carb, adding max dose metformin (2500 mg per day but ramp up to that as GI issues can be a problem but you will adapt to them over time), and exercising. I've been able to maintain it now that I've lost it, without as much cardio as when I was in losing it mode.
So, it CAN work. Not all studies show it works for weight loss, but I think if you also eat low carb and work to burn calories, you will lose weight.
Metformin has been a game changer for me, but my fasting sugars were (and even still are in 90's most days but not high 90's as before, and sometimes 80's) 90's to 100 and a few 101's (prediabetic is 101-125).
But, the goal is prevention! Metformin, for me, has been at least as potent a lifestyle improvement as was TRT...... It works great. I've been at a much healthier weight and body comp for 2 years now. TRT has also helped to be sure.
All the best.