Caffeine is an adenosine agonist (Opposite of melatonin) which indirectly increases dopamine.. That's why I focus much better after drinking a very strong coffee in the morning after the Vyvanse kicks in + nicotine too.

Sleep deprivation causes dopamine receptors to be more sensitive? Can have an antidepressant effect but can also cause mania/psychosis.

Ketosis agonizes adenosine receptors as well =]