The participants took 75 milligrams to 10 grams of barberry or 200 to 480 milliliters of barberry juice daily for 3 to 12 weeks.

Barberry improved the following markers of metabolic syndrome:

Systolic blood pressure (−9.84 mmHg)
Diastolic blood pressure (−11.31 mmHg)
Weight (−1.48 kilograms or −3.26 pounds)
Blood lipids: LDL (−11.38 mg/dL), triglycerides (−23.63 mg/dL), HDL (+2.46 mg/dL)
Glycemic control: Fasting blood glucose (−16.69 mg/dL), insulin (−1.70 mU/L), and HOMA-IR (−0.95), but HbA1c was unchanged.

The evidence quality was rated as high for lipid outcomes, moderate for insulin, and low to very low for the others.

Could barberry be a helpful add-on for metabolic syndrome? Original paper