Based on NIH | Is it safe to take Metformin with fish oil supplements, or are there any interactions to be aware of?

Most people can take metformin and fish oil (omega‑3) together without a known harmful interaction, and this combination is generally considered safe. ^{[1] [2]} There is no established direct drug–drug interaction listed in official metformin labeling with omega‑3 supplements, and fish oil’s common interactions do not include metformin. ^{[3] [4]}

What official information says

• Metformin’s official prescribing information highlights several clinically significant interactions (for example, with carbonic anhydrase inhibitors and certain drugs that raise metformin levels), but omega‑3/fish oil is not listed among them. ^[3]
• Consumer and professional versions of metformin extended‑release labeling advise discussing all prescription, over‑the‑counter, vitamin, and herbal products with your clinician but do not identify fish oil as an interaction of concern. ^{[5] [6]}

Fish oil safety and typical interactions

• Fish oil supplements are generally safe when taken as recommended, though they can cause mild side effects such as fishy aftertaste, heartburn, nausea, or diarrhea. ^[2]
• Higher doses of fish oil may increase bleeding tendency, so caution is advised with anticoagulant or antiplatelet drugs; fish oil may also slightly lower blood pressure and interact with certain other products (for example, orlistat can reduce fish‑oil absorption). ^{[7] [4]}
• Prescription omega‑3 (omega‑3‑acid ethyl esters) labels note prolonged bleeding time has been observed in some trials, though within normal limits and without clinically significant bleeding events in studied settings. ^[8]

Clinical data related to metformin and omega‑3

• A pharmacokinetic study comparing metformin given with ethyl eicosapentaenoic acid (EPA) found that co‑formulation did not improve metformin availability; when taken separately under fasting conditions, metformin exposure was actually higher than with a combined solid dose, suggesting no absorption advantage from taking them together. ^[9]
• Randomized data in people with type 2 diabetes on stable metformin showed that adding high‑dose EPA+DHA (about 2.8 g/day of EPA+DHA) could modestly raise fasting glucose and HbA1c, although effects varied and were mitigated when combined with another insulin‑sensitizing drug (pioglitazone). ^[10]
• Broader meta‑analyses of omega‑3 in type 2 diabetes suggest triglycerides decrease, while average effects on HbA1c and fasting glucose are small overall; some subgroups (for example, specific ethnic groups or EPA/DHA ratios) showed slight increases in fasting glucose. ^[11]

What this means for you

• Based on current evidence, there is no clear, direct interaction between metformin and fish oil that would routinely prevent taking them together. Most users can take both safely. ^{[3] [2]}
• If you use blood thinners (for example, warfarin, apixaban) or antiplatelet agents (for example, aspirin, clopidogrel), it’s sensible to check with your clinician before starting higher‑dose fish oil because of a potential increase in bleeding tendency. This caution is about fish oil itself, not metformin. ^{[7] [8]}
• If you plan on high doses of omega‑3 (typically ≥2 g/day of EPA+DHA), it may be reasonable to monitor blood sugars and HbA1c after starting, since some studies observed small increases in glycemic measures in certain situations. ^{[10] [11]}

Practical tips for taking them together

• Take metformin as prescribed with meals if recommended (especially extended‑release forms) to reduce stomach upset, and take fish oil with food to improve tolerance and reduce reflux. ^{[5] [2]}
• Keep your healthcare provider informed of all supplements; bring an updated medication list to visits. This helps your clinician evaluate bleeding risk, blood pressure, and glucose changes. ^{[5] [7]}
• If you notice unusual bruising, nosebleeds, or black stools while on fish oil especially if combined with blood thinners seek medical advice. These can be signs of increased bleeding. ^{[7] [8]}

Bottom line

• There is no documented, clinically significant interaction between metformin and fish oil supplements, and they are commonly taken together. ^{[3] [2]}
• The main considerations are fish oil’s potential bleeding risk at higher doses (especially with anticoagulants/antiplatelets) and a possible small effect on glucose control in some people at higher omega‑3 doses. Discuss planned doses and your full medication list with your clinician, and consider routine monitoring of glucose and HbA1c after starting or changing omega‑3. ^{[7] [11]}