The purpose of this study is to evaluate the long-term safety and tolerability of NKTR-118 treatment of opioid-induced constipation (OIC) in patients with non-cancer-related pain.

Inclusion Criteria:

• Provision of written informed consent prior to any study-specific procedures.
• NEW PATIENTS ONLY: Self-reported active symptoms of OIC at screening (<3 SBMs/week and experiencing >1 reported symptom of hard/lumpy stools, straining, or sensation of incomplete evacuation/anorectal obstruction in at least 25% of the BMs over the previous 4 weeks); and Documented confirmed OIC (<3 SBMs/week on average over the 2-week OIC confirmation period.
• PATIENTS ENROLLING FROM OTHER NKTR-118 STUDIES: Receiving a stable maintenance opioid regimen consisting of a total daily dose of 30 mg to 1000 mg or oral morphine, or equianalgesic amount(s) of 1 or more opioid therapies.
• FOR PATIENTS RANDOMIZED TO RECEIVE NKTR-118: Willingness to stop all laxatives and other bowel regimens including prune juice and herbal products throughout the 52-week treatment period, and to use only bisacodyl as rescue medication if BM has not occurred within at least 72 hours of the last recorded BM.

Exclusion Criteria:

• Patients receiving Opioid regimen for treatment of pain related to cancer.
• History of cancer within 5 years from first study visit with the exception of basal cell cancer and squamous cell skin cancer.
• Medical conditions and treatments associated with diarrhea, intermittent loose stools, or constipation.
• Other issues related to the gastrointestinal tract that could impose a risk to the patient.
• Pregnancy or lactation.