Shuiniujiao Dihuang Decoction With Variation for the Treatment of Psoriasis

Inclusion Criteria: * Mild to moderate chronic plaque psoriasis (PASI score 3 to 12). * Willingness to give informed consent. Exclusion Criteria: * Pustular or generalized erythrodermic psoriasis. * Psoriatic arthritis with syndrome of spleen-kidney yang deficiency according to Chinese medicine theory. * Systemic therapy for psoriasis 6 months prior to baseline. * Use topical medications for psoriasis 14 days prior to baseline such as retinoids, corticosteroids, vitamin D analogues, tazarotene and tacrolimus. * Has taken any antibiotics, probiotics and prebiotics 30 days prior to baseline. * UV light therapy 30 days prior to baseline. * Clinically significant laboratory abnormality in blood, liver or renal functions (≥1.5 times the upper limit of reference range). * History of allergy to Chinese herbs. * Known pregnant or lactation, or have a plan to conceive in 6 months. * Known active gastric or duodenal ulcer, or severe arrhythmia. * Unwillingness to comply with study protocol. * Any other condition that in the opinion of the investigators could disadvantage the subject.