My ADHD medication (yes, stimulants - and a pretty high dosage in my case) causes me to slow down and sleep. Then I wake up about an hour or so after taking it and am a normal person. I was diagnosed as an adult, but this was always the case for me - as a teen I drank 3 redbulls in the evening and went to sleep, because I finally could as my brain stopped keeping me awake with millions of thoughts.

I would drink about a pot of coffee per day as a teenager, throughout the day. Never had any impact on my sleep either, which I always assumed was just tolerance.

Turns out once medicated, if I have caffeine after about 15:00 I’m in for a bad night. Brains are extremely weird.