This. People assume that hunger is the same for everyone, and that can be used to simply rank the level of willpower people are exerting against the drive. But

This. People assume that hunger is the same for everyone, and that can be used to simply rank the level of willpower people are exerting against the drive. But it's not. Some people have different appetites which leave them skinny or permanently hungry. Some people can and do eat a lot more than others for less weight gain. This is why the drugs are so effective: they're appetite suppressants.