Thestrup‐Pedersen 1984.

Methods	Cross‐over trial Number of centres not stated Period of inclusion not stated
Participants	Inclusion criteria Age > 17 years Exclusion criteria Pregnancy Liver insufficiency Uncontrolled cardiovascular disorder Uncontrolled diabetes Clinical evaluation was performed before and after 4 and after 8 weeks Baseline data: colchicine 0.5 mg 3 to 4 times per day according to weight vs placebo (n = 27) Median age (range), years: 58 (19 to 80) Male/female: 5/22 Proportion of participants with psoriatic lesions elsewhere: 6/27 Withdrawal: 1 dropout (reason not mentioned)
Interventions	Intervention 1 A: colchicine 0.5 mg (3 to 4 times per day according to weight) (27 participants, cross‐over design) Intervention 2 B: placebo (3 to 4 times per day) (27 participants, cross‐over design) Co‐interventions: none Duration of treatment: 8 weeks
Outcomes	No primary or secondary outcome pre‐specified Score (resolved/improved/unchanged/worsened) according to pustule formation, redness, and scaling Side effects
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The patients received Tablet A for four weeks and Tablet B for another four weeks" Comment: insufficient information about the sequence generation process to permit judgement
Allocation concealment (selection bias)	Unclear risk	Comment: no information on method to guarantee allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "double‐blind placebo‐controlled. Drugs were added to placebo to give a bitter taste equal to tablets with colchicine" Comment: we consider blinding at low risk for trial vs placebo with no obvious clinical adverse events or known specific taste of experimental drug
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "double‐blind placebo‐controlled" Comment: we consider blinding at low risk for trial vs placebo with no obvious clinical adverse events or known specific taste of experimental drug
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "One patient received colchicine, but not placebo" Comment: only 1 dropout in the placebo group
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results