system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does coffee/caffeine make you lose your appetite?
gpt
It is a stimulant. Stimulants suppress your appetite; diet pills are stimulants. ADHD meds like Ritalin are stimulants, and patients often lose weight. 

Stimulants prepare the body for activity, and food in your guts makes that difficult.