Heroin is as close to "a perfect happiness drug" as anything human ingenuity has ever produced. My experience of its habitués tends to suggest that, while it's not impossible you'd become a better person under its effects, it is quite unlikely.
Alternately, I could make a solid case for MDMA. A huge rush of serotonin is closer to 'happiness' in my book; tickling the mu-opoid is more of a 'bliss' kinda thing.
If there were a beverage that worked like coffee except was more MDMA like, that our physiology could sustain in daily use, I dare say a lot of us would drink it.
It can be tricky from the outside to distinguish someone who's nodding from someone who's sleeping, but from the inside the two states aren't all that similar.
