The Effect of Naldemedine on Opioid-induced Bowel Dysfunction

Inclusion Criteria:

• Healthy (assessed by a study-affiliated medical doctor)
• Signed informed consent
• Able to read and understand Danish.
• Male (to avoid influence of menstrual cycles).
• Northern European descent (to minimize genetic variance influences on drugmetabolism).
• The researcher believes that the participant understands the study details, iscompliant and is expected to complete the study.
• Opioid naïve (no history of opioid use/addiction. Opioid use more than a year ago totreat pain post-surgery is accepted. Opioid use in connection with participation in aclinical trial more than a year ago is accepted)
• Between 20 and 40 years of age.
• A STAI (Spielberger State-Trait Anxiety Inventory) score in the range of 20-37 i.e.,classified as "no or low anxiety" at inclusion.

Exclusion Criteria: Known hypersensitivity or allergy towards the used pharmaceutical compounds orpharmaceutical compounds similar to those used in the study.

• Less than three spontaneous bowel movements per week.
• Participation in other studies within 14 days prior to first visit.
• Expected need of medical/surgical treatment during the study.
• Any diagnosed disease, which investigator concludes will affect the trial (includingall contraindicated complications: severe chronic obstructive pulmonary disease,pulmonary heart disease, severe bronchial asthma, paralytic ileus, hypercapnia,serious respiratory depression with hypoxia, moderate to severe decreased liverfunction, gastrointestinal obstruction or perforation, acute surgical abdominalcomplications such as appendicitis, Mb. Crohn's, ulcerative colitis, and toxic megacolon). History of substance abuse (alcohol, tetrahydrocannabinol, benzodiazepine, centralstimulants and/or opioids, urine drug test will be performed prior to treatment start).
• History of major mental disorders (e.g., major anxiety, major depression or treatmentwith psychoactive medications etc.)
• Metal implants or pacemaker.
• Daily use of prescription only medicine
• Daily alcohol consumption
• Participation motivated by "wrongful" reasons such as poor economy or psychosocialissues e.g., problems in the family, loneliness, sadness. People with such problemsmay be more likely to develop substance dependence*.
• Intake of alcohol within 48 hours before start of study period or any alcoholconsumption during each study period. If consumption takes place during the study theparticipant will be excluded.
• Use of any analgesic medication within 48 hours before start as well as for theduration of the study. If consumption takes place during the study the participantwill be excluded.
• Nicotine use