Oxycodone 5mg is used to relieve pain severe enough to require painkiller treatment and when other pain medicines did not work well enough or cannot be suffered. Oxycodone acts on the central nervous system of the brain to relieve pain. Oxycodone 5mg pills take 4 to 6 hours to work. Some common oxycodone side effects are; Feeling or being sick, stomach discomfort, feeling sleepy or tired, feeling dizzy and a sensation of spinning, confusion, headaches, itchiness or rash.