Study terminated due to halt in funding; may resume recruiting in future

The purpose of this study is to examine the acute agonist and antagonist effects of a full opioid agonist medication, an opioid antagonist medication, and a partial opioid agonist medication in individuals who have different levels of physical opioid dependence.

The pharmacological effects of opioids in opioid dependent individuals can vary as a function of the characteristics of the opioid being studied (e.g., whether it is an agonist, partial agonist, or antagonist; the dose administered; and the route of administration). Another important set of factors influencing the effects produced by opioids is the characteristics of the organism to which the opioid is being administered. One such characteristic is the level of physical dependence in individuals.

Participants in this study will be maintained on different dose levels of an opioid agonist (methadone). The participant will be challenged with a prototypic opioid agonist, antagonist, and a mixed agonist-antagonist with partial agonist features in order to determine the effects that each has on the human body.

Inclusion Criteria:

• Active opioid dependence
• Qualifies for opioid agonist treatment (e.g., methadone or buprenorphine)
• Fulfills DSM-IV diagnostic criteria for opioid dependence

Exclusion Criteria:

• Significant medical problems, including insulin dependent diabetes mellitus
• Non-substance use psychiatric disorders (e.g., schizophrenia)
• Currently seeking treatment for substance abuse