Ithink the worry with these is more about people using them improperly, or that they will create an impression among people that there is a kind of quick solution so they don't need to worry about good habits.
The risk benefit trade off is always a factor of course, so significant obesity where the person hasn't made progress with diet changes etc it makes sense.
But if someone isn't willing to make those kinds of changes then they are really not going to benefit from setting up a situation where they are going to go on and off a drug and up and down in their weight.
And it's open to some pretty significant abuse obviously - people trying to get to very low weights, people under pressure to keep their weight low (models, say) people who have eating disorders. I can see in some groups there could also be pressure to use it from outside, dance schools, even boxers.
In general using drugs to modify our behaviour on the regular isn't likely to create a healthy society because it prevents us asking why we want or need to modify behaviour in the first place, and doing something about it.
If it maintains a medical usage, I think that's the right approach but I think there will be a lot of pressure for it to become something else. You can see how many people think, even though they don't really qualify, that they should be entitled to it, because their reasons are just so important.