Insulin is abused by some bodybuilders as yet another gimmick in the quest for more size. There are likely other such niche uses/abuses, but that's one that came to mind.
Sounds like an incredibly miserable way to live, honestly.
My favourite junk food, and one that puts me KO for 3 days is a double cheese pizza.
Makes me depressed and despondent, bloated and my ADHD meds stop being effective (but my usual dose is quite low on purpose). But that's because of my physiology, the opioid effect is in the strong craving, and how lovely the first bite is, and how I hate myself after the first bite, for having succumbed to its allure once again.
Gluten and casein are under-researched. The fact that there is a so called "gluten sensitivity" fad is not a shared hallucination, but some effect we haven't identified or understood yet.