Based on NIH | Does metformin interact with fish or fish oil in a way that increases the risk of side effects?

Most people can take metformin with fish or fish oil (omega‑3 supplements) without a known harmful interaction, and there is no established increase in metformin‑related side effects from eating fish or taking standard omega‑3 products. ^[1] Evidence shows food can lower and delay metformin absorption a bit, but this is a general food effect and not specific to fish. ^[2] In a small pharmacokinetic study using prescription EPA (icosapent ethyl), metformin absorption under fasting conditions was actually higher when the two were taken separately rather than in a combined solid dose, while no difference appeared under fed conditions, suggesting no meaningful advantage or safety concern with routine co‑administration. ^[3]

What official labels say

• Metformin’s label lists several potential drug interactions (for example, with certain cationic drugs), but it does not identify fish or omega‑3 fatty acids as interacting agents. ^[4] Metformin absorption is decreased and slightly delayed by food in general (about 25–40% reduction in exposure and peak level with a single 850 mg dose), which is a class‑wide food effect rather than a fish‑specific interaction. ^[2]
• Omega‑3 prescription products (omega‑3‑acid ethyl esters) carry a precaution about possible prolongation of bleeding time, especially when combined with anticoagulants or other drugs that affect clotting; this is unrelated to metformin’s mechanism. ^[5] Omega‑3 labels recommend monitoring if you are on blood thinners, but they do not list metformin as a problematic co‑medication. ^[6]

What clinical studies suggest

• A pharmacokinetic comparison examining metformin with ethyl eicosapentaenoic acid (EPA) found that delivering both in one combined tablet did not improve metformin’s availability versus taking them separately; under fasting conditions, metformin exposure was higher when taken separately from icosapent ethyl, and in the fed state there were no group differences. ^[3] This points to no clinically important adverse interaction, and it supports standard separate dosing if taken fasting. ^[3]

Side effect considerations

• Metformin commonly causes gastrointestinal symptoms (nausea, diarrhea), which are usually milder when taken with meals; this mitigation is due to the general food effect and is not specific to fish or omega‑3s. ^[7]
• The rare but serious metformin‑associated lactic acidosis risk is linked to factors like significant kidney impairment and other contraindications, not to fish or omega‑3 intake. ^[7]
• Omega‑3 products may slightly prolong bleeding time; this is a consideration mainly for those on anticoagulants or with bleeding disorders, not an interaction with metformin. ^[5]
• Overall, metformin as monotherapy is unlikely to cause hypoglycemia, and adding omega‑3s does not change that expectation. ^[7]

Practical guidance

• It is generally reasonable to continue metformin while eating fish or taking standard doses of fish oil, as there is no recognized harmful interaction between them. ^[1]
• If you take prescription EPA (icosapent ethyl) while fasting, taking metformin and EPA at separate times may modestly favor metformin exposure, though this has not been shown to affect clinical outcomes. ^[3]
• If you experience stomach upset, taking metformin with meals (fish included) can help, acknowledging that food slightly lowers and delays metformin absorption without known harm to glucose control. ^[2]
• If you also use anticoagulants (like warfarin) or antiplatelets, discuss omega‑3 use with your clinician because of the bleeding‑time precaution; this is unrelated to metformin but is important for overall safety. ^[5]

Bottom line

• There is no established harmful interaction between metformin and fish or fish oil, and routine use together does not appear to increase metformin‑related side effects. ^[1]
• Food in general lowers and delays metformin absorption slightly, which can reduce stomach side effects, and this effect is not specific to fish. ^[2]
• Prescription omega‑3s carry a bleeding‑time precaution with blood thinners, but not with metformin. ^[5]
• A small study with EPA showed no clinically meaningful advantage to combining EPA and metformin in one pill and suggested separate dosing may modestly improve metformin exposure when fasting. ^[3]