IntroductionOpioid-induced constipation is a clinically relevant side effect and a cause of potentially avoidable drug-related hospital admissions.ObjectivesTo describe the presence of laxative co-medication, the reasons for not starting laxatives and to evaluate changes in stool patterns of opioid initiators.MethodsIn this observational study community pharmacists evaluated the availability of laxative co-medication in starting opioid users and registered reasons for non-use. Two opioid initiators per pharmacy were invited to complete questionnaires (‘Bristol stool form scale’ and ‘Rome III Diagnostic Questionnaire for the Adult Functional Gastrointestinal Disorders’) on their defecation prior to and during opioid use. Descriptive statistics and Chi square tests were used to analyse reasons for non-use of laxatives and changes in defecation patterns.ResultsEighty-one pharmacists collected data from 460 opioid initiators. Of those, 344 (74.8%) used laxatives concomitantly. Main reason not to use laxatives was that either prescribers or patients did not consider them necessary. Sixty-seven (89.3%) of the 75 opioid starters with two questionnaires completed were not constipated at opioid start. Eleven of them (16%) developed constipation during opioid use (Chi square p=0.003). At follow-up within laxative users 10.6% were constipated compared to 20.7% in subjects without laxatives.ConclusionOne in four opioid starters did not dispose of laxative co-medication, mainly because they were not considered necessary by either the prescriber or the patient. The prevalence of constipation doubled during opioid use. A watchful waiting strategy for the use of laxative co-medication might include a monitoring of defecation patterns with validated questionnaires.