For one of my friends, metformin was the key for finally losing weight. It got their insulin resistance under control, which had been causing them to crave food constantly throughout the day, way more than someone with normal insulin sensitivity. They never realized most people are not constantly hungry and thought people who were thinner just had way better impulse control or something, and that giving into that craving was some kind of personal failure of willpower, etc etc. When in reality it would've taken drastically more willpower for them to try to eat the same amount of calories a day that I do, because of this underlying biological situation.
The thing that gets me about all this, though, is how long it took for them to find a doctor that recognized what they needed in order to lose weight was treatment for the insulin sensitivity, rather than admonishments to "eat less." There must be so many other people with a treatable condition being written off in the same way.