Methods of decreasing abuse potentials of oral opioid dosage forms are described. In the methods, an opioid antagonist in a substantially non-releasable form is included in oral dosage forms comprising an opioid agonist. When the dosage form is chewed, crushed, heated or dissolved in a solvent, and then administered orally, intranasally, parenterally or sublingually, the opioid antagonist is released and at least partially blocks effects of the opioid agonist. Methods of preparing oral opioid dosage forms having decreased abuse potential are also described.