3. No contributive studies.

Study ID	Interventions and comparisons	Number randomised	Comments
Fairris 1984	Superficial X‐ray therapy vs placebo	6	Lack of numerical results
Hattel 1974	Hydroxyurea vs placebo	13	Lack of numerical results
Fredriksson 1978	Oral RO 10‐9359 (25 mg thrice per day) vs oral RO 10‐9359 (200 mg twice per week)	30	Non‐pertinent outcome (decreased number of pustules)
Thune 1982	Tigason vs placebo	42	Lack of numerical results for addressed outcomes (for remission, we have results for Tigason group but not for placebo group)
Foged 1983	Etretinate vs placebo	50	Lack of numerical results
Schroder 1989	Etretin vs placebo	30	Lack of numerical results and non‐pertinent outcome (decreased number of pustules)
Lassus 1988	Acitretin vs etretinate	60	Lack of numerical results
Lindelof 1990	Grenz rays vs placebo	17	Lack of numerical results
Matsunami 1990	Etretinate vs no treatment	20	Lack of numerical results
Erkko 1998	Ciclosporin vs placebo	58	Non‐pertinent primary outcome (reduction of 50% or more in the number of fresh pustules) and lack of numerical results for other outcomes
Bhushan 2001	Liarozole vs placebo	15	Numerical results available only for patients achieving PPASI 75 (not 100% or 50%)
Nielsen 1995	PUVA therapy vs placebo (with clobetasol as co‐intervention)	22	Cross‐over study results from first phase not reported separately
Rodriguez 2000	Aluminium chloride hexahydrate vs placebo	12	Lack of numerical results
Rosen 1987	Etretinate + PUVA therapy vs etretinate vs PUVA therapy vs placebo	20	Randomisation of participants, then of sides; number of randomised participants in UVA or no treatment was not available

PPASI: Palmo‐Plantar Area and Severity Index.

PUVA: combination of psoralens and long‐wave ultraviolet radiation.

UVA: ultraviolet A.