Metformin

What it means

Metformin is usually the first medicine prescribed for type 2 diabetes. It reduces how much sugar the liver releases and helps the body respond to insulin. It rarely causes low blood sugar on its own.

It is not approved for weight loss, but it tends to be weight neutral or cause a small loss. In the Diabetes Prevention Program, adults with prediabetes who took metformin were less likely to develop diabetes than those on placebo, though lifestyle change worked better.

Common side effects are diarrhea, nausea and stomach upset, which an extended-release form or slow start can ease. Long-term use can lower vitamin B12 levels, so periodic checks are often advised. The label carries a boxed warning for lactic acidosis, a rare but serious problem linked mainly to kidney or liver failure.

Some insurers require metformin first before covering a brand diabetes medicine.

Why it matters

Metformin often shows up in step-therapy rules and alongside GLP-1 medicines, so knowing its modest weight effect sets fair expectations.