The Ninth Doctor discovered the use of poppa packs when he went back with Rose Tyler to Neanderthal times and discovered a group of humans using them. Poppa packs contained many types of drugs to help many illnesses and sickness, but the drugs could not stop death.
The poppa packs could be refilled and had a number plate on it so they were able to select which combo of drug they wanted. People who wouldn't use poppa packs and thought they were wrong were called Refusers.
However, although they wouldn't use poppa packs, they would still use other drugs, such as drugs that would stop them needing the toilet. Poppa packs had a side effect on humans. Poppa packs would stop them thinking properly and would leave them not self aware, thus thinking everything was fine. (PROSE: Only Human)