The purpose of this study is to evaluate the safety and efficacy of a range of oral SP-333 doses for the treatment of opioid-induced constipation (OIC) in adults with non-cancer pain taking opioids.

Inclusion Criteria:

• Must be receiving chronic, stable opioid therapy to treat non-malignant pain for at least 3 months prior to screening
• Must have active OIC at screening
• Active OIC must be confirmed during baseline screening bowel habit and symptom diary
• Must be on stable diet

Exclusion Criteria:

• Has history of chronic therapy for chronic constipation prior to start of opioid therapy, or any potential non-opioid cause of bowel dysfunction that may be a major contributor to the constipation (i.e., mechanical obstruction or pseudo-obstruction)
• Use of medications that might affect bowel movement frequency or constipation-related symptoms (e.g., prokinetics, anti-diarrheal agents, laxatives other than study-defined rescue laxative)
• Has history of or current cancer (other than basal cell or squamous cell carcinoma of the skin) unless the malignancy has been in complete remission without maintenance chemotherapy for at least 5 years
• Unstable thyroid disease