Lin YK, et al. - The goal of this research was to determine the optimal concentration of indirubin in a topical preparation vs indigo naturalis ointment in the treatment of psoriasis. Findings disclosed 200 μg/g to be the most effective concentration. Topical indirubin appeared to be beneficial in psoriasis, displaying an efficacy between that of a topical medicine called calcipotriol and the combination of calcipotriol with a potent corticosteroid, with lesser toxicity when compared to the latter.