Oka 1990.

Methods	Multicenter double‐blind, placebo controlled randomised clinical trial with parallel group design (two interventions groups). Trial duration: 24 weeks. Follow‐up: 4 patients receiving ursodeoxycholic acid and 3 placebo dropped out.
Participants	Country: Japan. Number of patients randomised: 52, from 13 departments in Japan, mean age 59 years (91% females). Inclusion criteria: ‐ PBC was diagnosed clinically and histologically. Exclusion criteria: ‐ patients with severe symptoms or having received other medications for their PBC within the last three months.
Interventions	Patients were randomly assigned to receive: Intervention group 1: ursodeoxycholic acid 600 mg/day in three divided doses, n = 26; Intervention group 2: placebo, n = 26.
Outcomes	Symptoms (itching). Complications (oesophageal varices). Liver biochemistry. Serum cholesterol. Serum bile acids.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	The trial is described as randomised, but the method of sequence generation was not specified.
Allocation concealment (selection bias)	Low risk	Allocation was controlled by a single monitor according to a randomisation scheme (1:1), so that intervention allocations could not have been foreseen in advance of, or during, enrolment.
Blinding (performance bias and detection bias) All outcomes	Low risk	"Placebo tablets could not be distinguished from ursodeoxycholic acid tablets".
Incomplete outcome data (attrition bias) All outcomes	Low risk	The numbers and reasons for dropouts and withdrawals in all intervention groups were described.
Selective reporting (reporting bias)	Low risk	Pre‐defined, or clinically relevant and reasonably expected outcomes are reported on.
Other bias	Low risk	The trial appears to be free of information that could put it at risk of bias.