A Single-arm, Study to Assess the Effect and Tolerability of Standardised Laxative Therapy (SLT) for the Reversal of Opioid-induced Constipation (OIC).

Inclusion Criteria: * Male or female subjects at least 18 years * Females less than one year post-menopausal must have a negative pregnancy test prior to the first dose of study medication, be non-lactating, and willing to use adequate and highly effective methods of contraception throughout the study. (A highly effective method of birth control is defined as those which result in a low failure rate (i.e. less than 1% per year) when used consistently and correctly e.g. sterilisation, implants, injectables, combined oral contraceptives, some intrauterine devices ((IUDs), hormonal), sexual abstinence or vasectomised partner). * Documented history of malignant or non-malignant pain that requires around-the-clock opioid therapy (WHO step II/III opioid analgesics). * Subjects treated with WHO step II/III opioid analgesics for at least 2 weeks prior to Screening Visit (Visit 1), who will continue with the opioid(s) over the proposed study period. * Subjects meeting the following criteria for OIC: * Subject and Investigator confirm that the Subject's constipation is induced, or worsened by the Subject's opioid medication (present at Screening) * Subjects with mean BFI score \> 30 at Visit 1 * Subjects with \< 3 complete bowel movements (CBMs) in the week preceding the Visit 1, based on Subject's retrospective memory in response to Investigator's question. * Subjects taking at least one laxative on regular basis (i.e. ≥2 intakes per week during the ≥2 weeks prior to screening) for the treatment of OIC. * Subjects must be willing to take SLT. * Subjects taking daily natural dietary fibre supplementation are eligible if they can maintain their diet throughout the study, and in the Investigator's opinion are willing and able to maintain adequate hydration. * Subjects must be willing and able (e.g. mental and physical condition) to participate in all aspects of the study, including use of medication, completion of subjective evaluations, attending scheduled clinic visits, completing telephone contacts, and compliance with protocol requirements as evidenced by providing written, informed consent. * In the Investigator's opinion the Subject's concomitant medication dose will remain stable throughout the study Period (here concomitant medications mean all medications besides opioids (standard and rescue opioid treatment)). Exclusion Criteria: Medical Conditions: * In the Investigator's opinion any contraindication and precautionary condition for laxative medication(s) used in the study as per the SmPC. * Subjects having any potential non-opioid cause of constipation that might be a major contributor. * Surgery within 2 months prior to the start of the Screening Visit (Visit 1), or planned surgery during the Screening and Treatment periods that may affect GI motility. * Subjects with colostomy or ileostomy. * Hospitalisation expected/planned within the study Period (e.g. planned hospitalisation for the treatment of a pre-existing condition before informed consent) which can affect the outcome measure analysis. Treatments/Medications: • Subjects presently taking, or who have taken opioid antagonist(e.g. naloxone, naltrexone and methylnaltrexone) or opioid antagonists containing products (e.g. oxycodone/naloxone, buprenorphine/naloxone, pentazocine/naloxone, tilidine/naloxone) \< 30 days prior to the start of the Screening Period. * Subjects already taking maximum daily dose of country specific SLT (both First and Second Line SLT) on a regular basis (i.e. ≥4 days per week) for the treatment of OIC. * Subjects receiving opioid substitution therapy for opioid addiction (e.g. methadone or buprenorphine). Additional Screening Exclusion Criteria for Subjects Suffering from Non-malignant Pain: \- Subjects who participated in a clinical research study involving a new chemical entity or an experimental drug within 30 days of study entry Additional Screening Exclusion Criteria for Subjects Suffering from Malignant Pain: * Subjects who have received a new chemical entity or an experimental drug within 30 days of study entry (defined as Visit 1). Concurrent participation in another clinical trial is not permitted except the epidemiological study performed to assess the long-term survival data. * Subjects with an expected life expectancy of \< 3 months.