Or medications. Some drugs and steroids lead to weight gain.
I doubt that is a real factor. There may be a slight change in metabolic rate from Beta blockers but increased appetite and more eating is the cause of most all other drug side effects. And, metabolic rate differences is a myth, or more accurately an excuse. Fat people use most of their calories keeping a poorly insulated bag of mostly water at almost 100 F all the time. And, some calories consumed by movement.