Abstract: The present invention relates to methods of treating opioid dependence, enhancing the treatment of opioid dependence, treating opioid withdrawal, or alleviating one or more opioid withdrawal symptoms in a subject, preventing or reducing the likelihood of opioid dependence relapse in a subject treated for opioid dependence, reducing the vulnerability of a subject to develop opioid dependence in adulthood following opioid exposure during adolescence, or treating pain in a subject, comprising administering a therapeutically effective amount of a N-methyl-D-aspartate receptor (NMDA) partial agonist to the subject. The present invention further relates to compositions comprising an NMDA partial agonist for use with the aforementioned methods.