The purpose of this study is to evaluate the safety, tolerability and efficacy of ALKS 37 when administered daily for 4 weeks to adults with Opioid-induced Constipation (OIC).

Inclusion Criteria:

• Are at least 18 years of age at time of consent
• Have a body mass index (BMI)of 19 to 35 kg/m2 at screening
• Are receiving prescribed opioid medication for the management of chronic, non-cancer pain
• Meet the criteria of OIC
• Agree to use an acceptable method of contraception for the duration of the study

Exclusion Criteria:

• Pregnancy and/or currently breastfeeding
• Clinically significant medical condition or illness (other than the condition for which the pain medication is being prescribed)
• Receiving treatment with opioid therapy for cancer-related pain, abdominal pain, scleroderma, and/or for the management of drug addiction
• Any gastrointestinal (GI) disorder (other than opioid-induced constipation) or GI structural abnormality known to affect bowel transit, produce GI obstruction, or contribute to bowel dysfunction
• Use of naloxone, Subutex or Suboxone, Revia, Relistor, or Entereg starting 15 days before the first study visit following screening until the end of the study
• Participation in a clinical trial of a pharmacological agent within 30 days before screening