The purpose of this clinical trial is to evaluate the safety and effectiveness on the clinical and biological parameters of reproductive-aged PCOS women after a 12-week metformin and/or probiotics administration.

Probiotics are live bacteria that offer a health benefit to the host when administered in adequate amounts. Probiotic supplementation is safe for use and has demonstrated beneficial effects for metabolic diseases such as obesity and diabetes. In this study, about 90 reproductive-aged women with PCOS will be enrolled. Participants will be randomly assigned into one of the following three groups: Metformin tablets (0.5g tid po), ProMetS probiotics powder (4g qN po), Metformin tablets (0.5g tid po) and ProMetS probiotics powder (4g qN po), for 12 weeks. Blood and stool samples will be collected before and after treatment. Fasting glucose levels, fasting insulin levels, sex hormone levels, serum lipid profiles, inflammation markers, other metabolic related parameters and change of gut microbiota and immune cells will be evaluated.

Inclusion Criteria:

1. Premenopausal between 18-40 years of age.
2. Diagnosed PCOS defined as 2003 Rotterdam diagnostic criteria.

Exclusion Criteria:

1. During the pregnancy and lactation period.
2. Significant impaired liver function, impaired renal function, mental disease, severe infection, severe anemia, severe heart disease and neutropenia disease.
3. Use of antibiotics within 3 months.
4. Symptoms of any infection at screening.
5. Immunodeficient or use of immunosuppressive drugs.
6. Use of products containing prebiotics or probiotics within the last 3 months.
7. Previous history of gastrointestinal surgery or disease (such as peptic ulcer, irritable bowel syndrome, inflammatory bowel disease or other gastrointestinal disorder).
8. Medical conditions or diseases that may affect subject safety or confound study results in the opinion of the investigator