Coffee is a very mild stimulant in comparison to amphetamines and similar.

Depending on your current health, other medications, and if you drink alcohol, stimulants can be relatively harmless to deadly. Mixing an upper and downer has a history of stopping hearts without warning.

They’re restricted for good reason. It sucks that some of us just need them to function normally (adhd,etc), but if you don’t need them be aware of the risks.