Regarding PCOS and hyperinsulinaemia
In PCOS

Hyperinsulinemia is seen in 50-70% cases of PCOS
Insulin induces LH to cause thecal hyperplasia and secrete androgens
Hyperandrogenism lowers the level of hepatic sex hormone binding globulin
Metformin treats the root causes, rectifies endocrine and metabolic function, improves fertility rate, used as insulin sensitiser
It reduces insulin level, delays glucose absorption, liver production of glucose and improves peripheral resistance
Metformin do not cause hypoglycemia in a normoglycemic women
Hyperinsulinaemia is observed in about 40% to 80% of women with PCOS
Metformin has many other health benefits
Metformin causes hypoglycaemia in normoglycaemic women
Hyperinsulinaemia stimulates hepatic synthesis of SHBG