caffeine. After a few days without it, one cup of coffee makes me the most jovial person in the world. Without caffeine im bitter, angry and irritable...
Ill also say USP labs PowerFull makes me feel good in the morning without a groggy after effect.
Werd up, man. The first week going caffeine(or stim free, in general) is quite possibly the worst week ever... then the first week back is like wanting to race against Kenyans!
Aside from this, the only stuff none stim is like herbal teas or what have you.