Hawthorne 1992.

Methods	Randomized controlled trial Double blind, placebo controlled Withdrawal study Sudy duration 1 year
Participants	Diagnosis of ulcerative colitis In remission (or chronic low grade activity or steroid dependent) On azathioprine for 6 months or longer Only patients in remission used for review: n = 67
Interventions	Azathioprine continued at variable dosing (median 100 mg/day), P.O. Compared to azathioprine withdrawal ‐ change to placebo Co‐medication ‐ continued from pre‐trial medication: Sulfasalazine 1‐4 g/day in 39 patients (mean 2 g/day) Mesalazine 0.8 to 3.2 g/day in 28 patients (mean 1.2g/day) None in 12 patients
Outcomes	Main: (time to) clinical relapse, one year relapse rate Secondary: adverse events
Notes	Additional information given by investigator, method of sequence generation was not remembered
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not explicitly discussed
Allocation concealment (selection bias)	Low risk	Centralised pharmacy‐controlled randomisation Quote: "Randomisation was performed in hospital pharmacies"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "double blind" Quote: "an equivalent number of placebo tablets of identical appearance"
Incomplete outcome data (attrition bias) All outcomes	Low risk	All withdrawals were noted and explained Intention‐to‐treat was followed
Selective reporting (reporting bias)	Low risk	All outcomes were reported
Other bias	Low risk	Nothing of note