At the beginning of chapter 9, Ponyboy enters his home and takes five aspirins before the rumble. At this point in the story, Pony is completely exhausted and stressed out. Pony has skipped town with Johnny, hid in an abandoned church, narrowly survived a church fire, and is suffering from a severe headache. Pony believes that taking five asprins will make him feel significantly better and will hopefully get rid of his headache before the rumble. What Pony actually needs is a stomach full of hearty food and some much-needed rest.
In addition to hoping that the asprins will make him feel better, Pony takes them to numb his body before the rumble. Although Pony is feeling exhausted and ill, he refuses to abandon his friends and desires to participate in the rumble. By taking five asprins, Pony hopes to feel good enough to compete in the rumble.
Pony may also overindulge in asprins because he has witnessed his friends do the same with alcohol. Pony is an impressionable adolescent and is influenced by his peers—which could motivate him to take five aspirins. Pony may also be self-medicating and hoping that the aspirins will make him feel better about Johnny's severe injuries or the possibility of being placed in a boys' home.