This study is a clinical trial being done to investigate the efficacy of drug BRS201 (hydroxocobalamin) as a treatment in patients with primary sclerosing cholangitis. Participation in this study will take 8 weeks long and the study is structured as a cross-over study in which participants will take the study drug for 4 weeks and a placebo drug for 4 weeks in a randomized order in the form of an oral medication. Participation may also involve receiving an IV dose of the medication. The study will require participants to attend 9 study visits, all of which will be remote. Participation will involve taking an oral medication twice daily, tracking the medication in a log, and getting blood drawn and giving a stool sample for a few lab tests throughout the study. For the lab tests, a research nurse will visit the participant in-home for the convenience of the participant.

Inclusion Criteria:

• A diagnosis of PSC for at least 6 months based upon cholangiography (ERCP or MRCP) demonstrating intrahepatic and/or extrahepatic biliary strictures, beading or irregularity consistent with PSC.
• ALP > 1.5 times the upper limit of normal (ULN) at screening.
• Subject must either be on a stable dose of ursodeoxycholic acid for > 6 months prior to screening or have been discontinued > 4 weeks prior to screening (enrollment of patients who are on UDCA will be limited to 60% of all enrolled patients).

Exclusion Criteria:

• Anticipated need for liver transplant within one year as determined by Mayo PSC risk score
• Evidence of decompensated liver disease such as variceal bleeding, ascites, or hepatic encephalopathy.
• Evidence of advanced liver disease including MELD score > 10, bilirubin > 3.0, platelet count < 100,000; or INR > 1.4
• Concomitant chronic liver disease including alcohol related liver disease, chronic hepatitis B or C infection, haemochromatosis, Wilson's disease, alpha1-antitrypsin deficiency, non-alcoholic steatohepatitis, autoimmune hepatitis, or primary biliary cholangitis
• Secondary causes of sclerosing cholangitis
• Patients who have a confirmed malignancy or cancer within 5 years except non-melanoma skin cancers
• Treatment with any investigational agents, within two months or 5 half-lives of the investigational product, whichever is longer.
• Active illicit drug or more than moderate alcohol consumption.
• Evidence of bacterial cholangitis within 6 months of enrollment
• In patients with Ulcerative Colitis, or, if Crohn's disease, a need for additional therapy at time of screening.
• Chronic kidney injury (eGFR < 60)
• Pregnancy or lactation
• Uncontrolled hypertension with a systolic BP > 140 and a systolic BP > 90
• Prohibited medications: current use of vitamin C and prednisone
• Patients with a history or risk of cardiovascular conditions, including arrhythmia, long QT syndrome, congestive heart failure, stroke, or coronary artery disease
• Patients with a history of kidney stones
• Congenital or acquired immunodeficiencies
• Other comorbidities including: diabetes mellitus, systemic lupus
• An episode of acute cholangitis within 4 weeks of screening Check eligibility here: https://redcap.link/Checkmyeligibility

This is a double-blinded study.