Psoriasis and metabolic disorders are well-known mutual comorbidities. The investigators hypothesized metformin can ameliorate both psoriasis and metabolic disorders mainly via gut microbiota modulation. The investigators design a randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of treatment of metformin for psoriasis combined with disorders of glucose and lipid metabolism and to explore the role of gut microbiota during the process.

Inclusion Criteria:

criteria 1 and 2 are both needed for inclusion:

1. included if all of the following criteria are met

   • ≥18 years and ≤75 years
   • Diagnosed according to Classification criteria for Psoriasis Vulgaris
   • Understanding the whole process of the study, voluntary participation and signed the informed consent

2. included if at least one of the following criteria is met

   • Body Mass Index (BMI) over 24
   • impaired glucose or insulin resistance

Exclusion Criteria:

• Pregnant women, or women who ready for pregnancy or lactating;
• Have special primary endocrine system lesions that can influence glucose or lipid metabolism
• More than 20% change of their predrug body weight within a half year
• Severe diabetes which needs combined therapy
• Known major systemic diseases like cancer, liver or kidney malfunction, etc.
• Alcohol abuse
• Known severe or chronic infections like tuberculosis or HIV
• Use of other systemic medication that could influence the metabolic level
• Patients participated in any clinical trials within 3 months
• Other cases which researchers believe that can not enroll

Study Protocol; Statistical Analysis Plan (SAP); Informed Consent Form (ICF); Clinical Study Report (CSR) can be shared for the purpose of academic communication

Since the official start of the trial to the end of the trial

Describe clearly about the reason of review.

Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)