- use of medications within 48 h of dose initiation; structural or metabolic diseases that affect the gastrointestinal system and functional gastrointestinal disorders; previous abdominal surgery other than appendectomy, cholecystectomy, hysterectomy, or hernia repair; known illnesses such as diabetes, cardiovascular or lung disease; current psychiatric disorders (anxiety, depression, substance use); use of agents that influence bowel habit, i.e. anticholinergics (not including antihistamines with anticholinergic properties), spasmolytics and prokinetics in the 7 days before the study.