Provided are methods for reducing the addiction potential and/or reducing one or more CNS-side effects related to the administration of an opioid analgesic drug by administering the opioid analgesic drug in the form of an oligomeric polyethylene glycol conjugate compound. The compounds provided demonstrate notably reduced potential for substance abuse, and possess altered pharmacokinetic profiles relative to the opioid agonists alone, but are not subject to the risk of physical tampering that allows for the recovery and abuse of the opioid agonist associated with certain alternative delivery formulations.