I believe there's far more iatrogenic obesity than is commonly recognised, particularly from medications for mental health.
It used to be that if you were severely depressed, a psychiatrist or possibly a GP would give you an antidepressant — a tricyclic or an MAOI. But they weren't handed out on a whim, because it was recognised that they had side effects and were risky in overdose. You only got them if you were really quite unwell. If you were psychotic, a psychiatrist would prescribe an antipsychotic, one of the old ones that caused movement disorders. Nasty drugs, but considered preferable to insanity.
Now, if you walk into any room full of people you can guarantee that a whopping chunk of them are taking the SSRI antidepressants that were so heavily marketed to doctors in the 1990s, or one of the related SNRIs, or another antidepressant like mirtazapine (which could make dental floss gain weight). Not only that, a good few of the people will be taking one of the modern antipsychotics, for sleep or for anxiety or to augment their antidepressant or for some other reason, and those don't just make you gain weight — sometimes dramatically — they actively change your metabolism to be more diabetic-like. Sometimes permanently. And these things are given out frequently, to people with no psychosis.
A while back I was on a college course for adult returners to education, and as we were all chatting in one of the breaks, it emerged that the majority of the class were on some kind of psychiatric drug, and a good few were taking quetiapine, one of the modern antipsychotic drugs which can cause high blood sugar and weight gain. This wasn't a course aimed at people with mental health problems, this was, on the whole, ordinary working-class men and (mostly) women who for whatever reason had ended up in the same place at the same time. And yes, lots of us were fat.