So, I OD'd on Ecstasy three days ago, or so. (only took one, and have only taken it occasionally) My Happiness still is barely half-refilled. Went to Switzerland, but the game said I wasn't addicted. Nothing I do seems to refill the Happiness, and every time I do actions within the game, my hard-earned Happiness gains disappear, of course.
I always use shrooms to recover my happiness. Those things take away 25 energy which makes them so useless and you gotta take 50 of them to get that merit.
Since Im in a faction, I use up my energy in attacks (you can probably try and collect bounties or do missions) then take a shroom when my energy is zero to gradually recover my happiness (400-500 happy per shroom). Takes 2 days max