Based on NIH | Does drinking green tea increase the risk of side effects when taking metformin?

Green tea and metformin: what we know Based on current evidence, typical green tea drinking (1–3 cups per day) does not appear to meaningfully increase the risk of metformin side effects for most people. Green tea is not listed among established metformin drug interactions or known causes of metformin-related complications such as lactic acidosis; alcohol is the major beverage specifically warned against with metformin. ^{[1] [2]} That said, concentrated green tea extracts (high-dose catechins like EGCG) can affect drug transporters and metabolism in experimental settings, so caution is reasonable with high-dose supplements rather than ordinary tea. ^{[3] [4]}

Key takeaways

• Ordinary green tea consumption is unlikely to cause harmful interactions with metformin in most users. ^{[1] [2]}
• Alcohol, not green tea, is the beverage clearly associated with higher lactic acidosis risk on metformin; heavy alcohol intake should be avoided. ^{[1] [5]}
• High-dose green tea extracts may influence drug absorption/transport in ways that could theoretically alter medication levels; these effects are more evident in lab and animal studies than in routine human tea drinking. ^{[3] [4]}
• Metformin alone rarely causes low blood sugar; combining with insulin or sulfonylureas increases hypoglycemia risk, independent of green tea. ^{[2] [5]}

What official labeling says about metformin interactions

Metformin’s official safety information emphasizes avoiding excessive alcohol because it increases the chance of lactic acidosis, a rare but serious side effect. ^[1] Alcohol moderation advice is repeated across metformin labels, and insulin/insulin secretagogues are highlighted for hypoglycemia risk when used with metformin. ^{[2] [5]} Green tea is not listed among established interactions in these documents. ^{[6] [7]}

What research says about green tea and drug interactions

Green tea catechins can bind some drugs and can inhibit or modulate drug-metabolizing enzymes and transporters (for example, intestinal and renal transporters) in vitro and in animals, which might alter drug absorption or elimination. ^[3] However, these effects have only been documented in limited human cases at common beverage doses; larger effects are more plausible with concentrated supplement forms. ^[3] Reviews of adverse events highlight that concentrated extracts, rather than brewed tea, are the primary concern for rare liver toxicity and potential drug interactions. ^[4]

Glycemic control context

Clinical studies of green tea or its extracts in diabetes show mixed or modest metabolic effects and do not demonstrate a consistent harmful interaction with metformin. ^{[8] [9]} Some trials suggest small improvements in insulin-related measures or waist circumference, but effects on fasting glucose and HbA1c are variable and often small. ^{[8] [9]} These findings do not indicate increased metformin side effects from drinking green tea. ^{[8] [9]}

Practical guidance

• Brewed tea: Drinking moderate amounts of brewed green tea is generally reasonable with metformin for most people. ^[3]
• Avoid excess alcohol: Limit or avoid heavy drinking because it raises lactic acidosis risk on metformin. ^{[1] [5]}
• Be cautious with supplements: If you are considering high-dose green tea extract capsules, it may be prudent to discuss with your clinician, especially if you have kidney or liver issues or take multiple medications that rely on renal transporters. ^{[3] [4]}
• Watch combined therapies: If you also use insulin or sulfonylureas, monitor for low blood sugar; this risk is related to those drugs, not green tea. ^{[2] [5]}
• Know general warning signs: Unusual fatigue, muscle pain, fast breathing, stomach discomfort, or feeling cold could signal lactic acidosis and warrant urgent care, regardless of tea use. ^{[1] [2]}

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Quick reference table

Topic	What labeling/research indicates	Practical point
Lactic acidosis risk	Alcohol increases risk on metformin; green tea is not listed. [1] [2]	Avoid heavy alcohol; green tea in usual amounts is acceptable.
Hypoglycemia	Rare with metformin alone; higher risk with insulin/sulfonylureas. [2] [5]	Monitor glucose if on combination therapy; green tea does not meaningfully change this risk.
Drug interactions	No established interaction with green tea in metformin labeling. [6] [7]	Routine tea drinking is unlikely to affect metformin exposure.
Green tea extracts	Can affect enzymes/transporters in vitro/animals; rare adverse events reported with concentrated extracts. [3] [4]	Use caution with high-dose supplements and discuss with a clinician.
Effects on glucose control	Mixed/modest benefits; no evidence of increased metformin side effects. [8] [9]	Do not rely on tea for glucose control; continue prescribed therapy.

Bottom line

For most people taking metformin, moderate brewed green tea intake does not appear to increase side-effect risks, while excessive alcohol clearly does and should be avoided. ^{[1] [2]} If you plan to use concentrated green tea extract supplements, consider discussing it with your healthcare professional because high-dose catechins can influence drug handling in ways not typically seen with ordinary tea. ^{[3] [4]}