This was last updated during game version Glimpse V.35033
Joy is a pill that the residents of Wellington Wells voluntarily consume to keep them happy and sedated, but more importantly, to forget the city's terrible past. This desire to forget, coupled with the exuberance Joy grants, causes residents to beat any Downers (those who choose to not take their Joy) to death, fearing that they might "remember".
There are currently three flavours of Joy pill available to the citizens of Wellington Wells: Vanilla, Chocolate, and Strawberry. It appears that these flavours are not provided for choice, but so a wider proportion of the population is able to ingest them, suggesting that the chemical composition of each flavour is slightly different. Wastrels are Wellies who are unable to take Joy for one reason or another, and a note from one unfortunate (dead) Wastrel reveals that she is waiting for the fourth flavour, Coconut, to become available. She hopes this will enable her to tolerate Joy, and like everyone else, forget the past.