A topic in Clinical Evidence summarizes the results one systematic reviews (search date 1999, 3 RCTs). It found that dithranol significantly improved psoriasis at 4–8 weeks compared with placebo (SMD -1.04, 95% CI -1.65 to -0.42), assessed by different scoring systems. One systematic review (search date 1989, 22 small RCTs) found no significant differences between short contact (shorter contact time at higher concentrations) and conventional treatment. Adverse effects of dithranol include smell, staining, and burning.