I'm not sure about caffeine, but amphetamine-based stimulants (adderall, vyvanse, etc) stimulate the production of both dopamine (the feel good chemical) and norepinephrine, aka the anti-adrenaline neurotransmitter. That's why it calms down people with ADHD, our brains don't create or transport neurotransmitters correctly (among other things). It's also why SNRIs are effective for some, they inhibit the brain's reuptake of norepinephrine. I'm personally on both and they help eachother work more effectively.