Based on NIH | Can metformin cause a skin rash, and how common is this side effect and what should I do if it occurs?

Metformin can cause skin rashes, but this appears to be uncommon and often mild. Allergic-type skin reactions such as itching (pruritus), redness (erythema), hives (urticaria), or morbilliform/maculopapular rashes have been reported; in some cases they may fade even if the drug is continued, but if the reaction persists the medication should generally be stopped. ^[1] In rare reports, more severe hypersensitivity reactions (e.g., angioedema or widespread exfoliative rashes) have been described with combination products that include metformin, which require urgent medical attention. ^[2]

How common is rash with metformin?

• In clinical experience summarized for glyburide-metformin combination products, allergic skin reactions like itching, redness, hives, and maculopapular rashes were documented in about 1.5% of patients exposed to the sulfonylurea component (glyburide); similar types of rashes have been noted in labeling for the combination, and persistent reactions should prompt discontinuation. ^[3] These reactions “may be transient and may disappear despite continued use,” but ongoing or worsening symptoms warrant stopping the drug. ^[4] Although this statistic comes from combination labeling where glyburide exposure is highlighted, the combination’s safety information acknowledges cutaneous hypersensitivity can occur in this setting, and persistence should lead to discontinuation. ^[5]

• Postmarketing safety sections for several metformin-containing products list hypersensitivity skin reactions (rash, urticaria, angioedema, and rarely severe exfoliative conditions) as reported events, though true frequency cannot be reliably estimated from voluntary reports. ^[6] Because postmarketing reports lack denominators, they cannot provide a precise rate, but they confirm that such reactions have occurred. ^[6]

What could the rash look like?

• Reported patterns include itchy red patches, hives, or a measles-like (morbilliform) or maculopapular eruption. ^[1] Rarely, more extensive or severe rashes have been reported in association with metformin-containing combinations, such as exfoliative conditions or features of anaphylaxis or angioedema (swelling of lips, tongue, face). ^[2]

What to do if a rash occurs

• If you notice a new mild rash (itching, scattered red bumps) after starting metformin, it can sometimes be transient; however, if the rash persists, worsens, or is bothersome, it is generally recommended to stop the medication and contact your prescriber to discuss next steps. ^[1] If you experience any signs of a serious allergic reaction such as hives with swelling of the face, lips, tongue, or throat, trouble breathing or swallowing, or widespread peeling rash stop the drug and seek urgent medical care. ^[2]

• When a rash is suspected to be drug-related, your clinician may consider alternatives for blood sugar control and, if needed, short-term symptomatic treatments (e.g., antihistamines for itch) while ensuring the suspected drug is discontinued if the reaction is persistent or severe. ^[1]

Distinguishing metformin from combination products

• Some labels that document dermatologic reactions come from fixed-dose combinations (e.g., glyburide/metformin or DPP-4 inhibitor/metformin), where either component could contribute to a rash; nonetheless, the guidance remains similar: report symptoms promptly, and discontinue the drug if reactions persist or are severe. ^[1] For products that pair metformin with agents known to cause hypersensitivity (e.g., sitagliptin), instructions specifically advise stopping the medication and seeking medical advice if allergic symptoms occur. ^[2]

Practical steps you can take

• Document timing: Note when the rash started relative to starting or changing the dose of metformin. Persistent rashes after initiation raise suspicion for a drug reaction and should be evaluated. ^[1]
• Check severity and associated symptoms: Any swelling of the face/tongue, breathing difficulty, or extensive blistering/peeling warrants emergency evaluation and permanent discontinuation. ^[2]
• Contact your clinician: If the rash is mild but does not resolve quickly, your clinician may advise stopping metformin and switching to another glucose-lowering option. ^[1]

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Quick reference table

Topic	Key points
Can metformin cause rash?	Yes, allergic-type rashes (itching, redness, hives, maculopapular eruptions) have been reported with metformin-containing products. [1]
How common?	Allergic skin reactions are documented around 1.5% with the glyburide component in combination labeling; reactions in metformin-containing products are reported postmarketing, but exact frequency for metformin alone is not well defined. [3] [6]
Mild rash action	May be transient; if persistent or worsening, discontinue and contact your prescriber. [1]
Severe reaction signs	Hives with facial/lip/tongue swelling, trouble breathing or swallowing, widespread peeling/exfoliative rash; stop drug and seek urgent care. [2]
Why not ignore?	Persistent or severe hypersensitivity can escalate; labeling advises discontinuation if skin reactions persist. [1]

If you notice a new skin rash after starting metformin, does it improve quickly or is it continuing or getting worse?