Inclusion Criteria:
* age 18 years or above
* Self-identification as White
* Confirmed moderate-severe bile acid diarrhoea with a SeHCAT test result of ≤ 10 %
* Reported number of average daily stools ≥ 3 stools per day
* Reported number of average daily watery (6 or 7 on the Bristol Stool Chart) stools ≥ 1 stools per day(30)
* Informed and written consent
Exclusion Criteria:
* Unwillingness to pause any of the following medications during the trial: bile acid sequestrants, morphine medication, liraglutide or anti-constipation medication (e.g., lactulose, laxoberal, magnesia)
* Unwillingness to pause any anti-diarrhoea medication (e.g., imodium) from 3 days before initiation of each stool diary until after the respective visit
* If regularly administering psyllium or metformin, unwillingness to agree to a stable dose of psyllium or metformin throughout the trial
* Concomitant use of any drug in the GLP-1 receptor agonist drug class with the exception of paused liraglutide, see above
* Concomitant use of any kind of insulin medication
* Planned major changes in food consumption throughout the trial, including planned weight loss attempts
* Prior use of any statin within the recent 6 months
* Intake of larger quantities of grapefruit juice during trial participation, at the discretion of the investigator
* History of/present hepatobiliary disorder (except for simple metabolic dysfunction-associated fatty liver disease) and/or alanine aminotransferase and/or serum aspartate aminotransferase ≥ 3 times upper limit of normal
* Crohn's disease, ulcerative colitis, celiac disease or lactose intolerance
* Previous intestinal resection or major intra-abdominal surgery incl. stoma (cholecystectomy and appendectomy not included)
* Nephropathy with estimated glomerular filtration rate \< 45 ml/min/1,73 m2
* Plasma level of creatine kinase ≥ 5 times the upper limit of normal
* A recent stroke or transient ischemic attack (within 6 months)
* Any treatment or condition requiring acute or subacute medical or surgical intervention
* Hypothyroidism or hyperthyroidism, if not well regulated, at the discretion of the investigator
* Active or recent (within 6 months) clinically significant malignant disease (non-melanoma skin cancer not included), at the discretion of the investigator
* Alcohol consumption exceeding 12 units/week for women or 18 units/week for men, respectively. These thresholds are based on the limits of the European Association for the Study of the Liver
* Drug abuse, at the discretion of the investigator
* Fertile women not using any of the following contraceptive methods for the duration of the trial until at least 5 days after end of trial: Hormonal (tablet/pill, depot injection of progesterone, subdermal gestagen implantation, hormone intrauterine devices (IUD), hormonal vaginal ring or transdermal hormonal patch) associated with inhibition of ovulation, chemical (copper IUD), sterilisation, vasectomised partner with a confirmatory test, or sexual abstinence per the investigator's discretion
* Pregnant or nursing women
* Known or suspected hypersensitivity to atorvastatin or any of the additives in the tablet
* Receipt of any investigational drug within 30 days prior to visit 0
* Concomitant treatment with any of the following (topical administration not included): ciclosporin, telithromycin, clarithromycin, delavirdin, stiripentol, ketoconazol, voriconazol, itraconazol, posaconazol, letermovir, ritonavir, lopinavir, atazanavir, indinavir, darunavir, bocepravir, telaprevir, elbasvir/grazoprevir, ledipasvir/sofosbuvir, erythromycin, niacin, ezetimibe, fusidic acid, gemfibrozil, colchicine, digoxin, warfarin
* Unable to speak or understand Danish or mental incapacity that preclude adequate understanding or cooperation or unwillingness to comply with trial requirements
* Active participation in any other clinical intervention trial (observational studies not included)
* Other concomitant disease or treatment that according to the investigator's assessment makes the person unsuitable for study participation
