The stadium where Daniel is abducted is supposed to be Estadio Nacional de Chile, but in the movie, it is the stadium Tomás Adolfo Ducó, which is the home of C.A. Huracán, a soccer team from Buenos Aires, Argentina.
The pills the cult members were forced to take were probably drugs to help make them more calm and compliant. A few possible examples are benzodiazepines, which are used to treat anxiety, and scopolamine, which has been used by cults in the past. Small doses of scopalamine are used for motion sickness, but large doses can make people very susceptible to suggestion.