This trial which will be conducted in two phases.~The first part of the study will be conducted as an internal feasibility test. Three patients with major LARS will be included. Patients will be recruited from the Department of Surgery, Zealand University Hospital. These patients will not be randomized nor blinded. They will receive a 4-week treatment with 25 mg melatonin and will undergo the same questionnaires and tests before and after treatment as in the randomized clinical trial. The preliminary results from the internal feasibility test will allow us to assess potential difficulties related to the administration or design, which then will be able to be corrected before the randomization part is initiated.~The second part of the will be conducted as a randomized, blinded, placebo-controlled, crossover study and will be testing whether treatment with melatonin has an alleviating effect on Low Anterior Resection Syndrome (LARS) symptoms.~Patients will be randomized to receive 4 weeks of treatment with melatonin, followed by a 4 week wash out period, and then 4 weeks of treatment with placebo (M-P) or 4 weeks of treatment with placebo, followed by a 4 week wash out period, and then 4 weeks of treatment with melatonin (P-M). Both participants and investigators will be blinded.~Patients will be given questionnaires before and after each treatment period to assess outcomes. Blood samples and rectal biopsies will be taken after each treatment period.
The primary objective of the study is to investigate whether treatment with melatonin has an alleviating effect on Low Anterior Resection Syndrome (LARS) symptoms. Secondarily, the effect of the treatment on bowel movements, other patient reported symptoms, quality of life, depression, anxiety, sleep disturbances, motilin levels, and microscopic changes in rectal mucosa will be investigated.