Does Metformin Interact With Phenytoin?

Name: Does Metformin Interact With Phenytoin?
Creator: OmniRx Health

Examples: Thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blockers, and isoniazid.

Reviewed by the OmniRx Health clinical team•Last reviewed Jul 4, 2026

Severity: Minor

Severity basis: drug interactions section. Combining Metformin (Biguanide antidiabetic) and Phenytoin (Anticonvulsant) is classified as a minor interaction.

What to Do

This is generally a minor interaction, but review it with your pharmacist to be sure it is safe for you.

How This Interaction Works

Interactions like this one can happen when two medicines have overlapping effects, or when one changes how the other is absorbed, broken down, or cleared from the body. Metformin is a biguanide antidiabetic and Phenytoin is a anticonvulsant; together they are documented as a minor interaction. How much this matters depends on your dose, your other medications, and your overall health.

If You Take Both Medications

If you have been prescribed both Metformin and Phenytoin, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.

From the FDA Label

Examples: Thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blockers, and isoniazid.

Source: FDA structured product labeling (set_id 011de1a5-1ac0-4831-9e8d-26ec79ba2205).

Metformin

Biguanide antidiabetic

Brands: Glucophage, Fortamet, Glumetza

View Metformin safety profile

Phenytoin

Anticonvulsant

Brands: Dilantin

View Phenytoin safety profile

Check these against your full medication list in our free Interaction Checker

Frequently Asked Questions

Can you take Metformin and Phenytoin together?

Metformin and Phenytoin have a documented minor interaction. This is generally a minor interaction, but review it with your pharmacist to be sure it is safe for you.

How serious is the Metformin and Phenytoin interaction?

It is classified as a minor interaction, based on the FDA label's drug interactions section. A minor interaction is usually limited in effect but is still worth discussing with your care team.

What should I do if I'm taking both Metformin and Phenytoin?

This information is educational — not medical advice.

This page is provided for general educational purposes and summarizes publicly available data from sources such as the U.S. Food & Drug Administration. It is not a substitute for the judgment of a licensed clinician and should not be used to start, stop, or change any medication. It may be incomplete or out of date, and individual circumstances vary. Always talk with your prescriber or pharmacist about your specific medications and health conditions. If you think you may have a medical emergency, call 911.

Questions About Your Medications?

A licensed OmniRx provider can review your full medication list and help you understand what's safe for you — no office visit required.

Other Metformin Interactions

Other Phenytoin Interactions

Sources & References

Learn more about where our data comes from and how we write and review medical content.