Metformin is the most widely prescribed diabetes medication and one of the most affordable prescription drugs available. As a generic medication on Tier 1 of virtually every formulary, metformin is covered with the lowest possible copay by all insurance types. Many plans and pharmacies offer metformin at $0 to $4 per month.
Key Facts
Check Your Specific Plan's Formulary
Coverage varies by plan. Use our formulary checker tool to look up your exact copay and restrictions.
Open Formulary CheckerSources and standards behind this page
Drug coverage in the United States is governed by published rules rather than by any one insurer's summary, and the sources below are the primary ones. They are linked so a reader can check a claim without taking this page's word for it.
- FDA Orange Book publishes the therapeutic-equivalence ratings that decide whether a generic may be substituted for a brand-name drug.
- FDA generic drug facts sets out what "generic equivalent" means and what a manufacturer must prove.
- CMS prescription drug coverage defines the rules a Medicare drug plan formulary must follow and how it may change mid-year.
- Medicare.gov drug coverage (Part D) states what a Part D plan is required to offer a member.
- CMS prescription drug appeals documents the coverage-determination and exception process when a drug is denied.
This page describes how coverage and formularies work. It is not medical advice, and a reader's own plan documents and prescriber decide what applies to them.
Frequently Asked Questions
Many insurance plans offer metformin at $0 copay, especially on ACA marketplace plans that cover certain preventive diabetes medications at no cost. Even plans with a copay rarely charge more than $5 to $10. Some pharmacy discount programs offer metformin for $4/month without insurance.
No. Metformin is one of the most affordable prescription drugs available. Walmart, Costco, and many other pharmacies sell generic metformin for $4 per 30-day supply without insurance. GoodRx and other discount card programs often bring the price below $10. Insurance is helpful but not necessary for metformin affordability.
Both immediate-release (IR) and extended-release (ER) metformin are generic and covered on Tier 1 by most plans. ER versions may be slightly more expensive but are still very affordable. Some brand-name ER formulations (like Glumetza) are much more expensive and may be on higher tiers.
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- Medicare Part D Formulary 2026
- Medicaid Drug Coverage 2026
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