Questions about Type 1 Diabetes...

Hello, I'm a screenwriter writing a screenplay and one of my characters is a diabetic. -- I hope it's okay if I post this question here. If not please just ignore but if you have some insight that you could lend, it would be much appreciated.

My character is a 17-year-old boy with type 1 diabetes. He's reckless and self-destructive, doing things like taking drugs (pot, MDMA) and drinking alcohol, and sometimes he even forgets to take a dose of insulin.

My question is, would skipping a dose even be possible? What kind of side effects could this have (immediate and long term)? What about the drugs - especially drugs that suppress appetite? What kind of problems could this cause?

Again, if I'm intruding here, I do apologize.

Kind Regards