Based on NIH | Can eating fish or taking fish oil supplements cause or worsen gastritis?

Most people can eat fish or take fish oil without causing or worsening gastritis, but a few may notice mild stomach symptoms such as heartburn, nausea, or indigestion especially at higher doses or on an empty stomach. ^[1] In general, fish oil is considered safe when taken as recommended, and there is no strong human evidence that it directly causes gastritis (stomach lining inflammation). ^[1]

What gastritis is and common causes

Gastritis means inflammation of the stomach lining and can be acute (short‑term) or chronic (long‑term). ^[2] The most common causes include Helicobacter pylori infection, regular use of NSAIDs (like ibuprofen or naproxen), and heavy alcohol use. ^[2] Food choices can trigger symptoms in some people, but they are usually not the root cause. ^[2]

What we know about fish and fish oil

• Fish oil safety profile: When used at standard doses, fish oil’s most frequent side effects are a fishy aftertaste, burping, heartburn, nausea, or diarrhea. ^[1] These effects are typically mild and dose‑related, and they can feel like “gastritis” even if true inflammation isn’t present. ^[1]
• Prescription omega‑3 products: Clinical trial data for omega‑3‑acid ethyl esters list burping (eructation), dyspepsia (indigestion), upset stomach, and taste changes as common gastrointestinal side effects. ^{[3] [4]}
• Bleeding risk at high doses: Very high intakes of fish oil may increase bleeding tendency, which is relevant for people with ulcers or those on blood thinners, although this is not the same as causing gastritis. ^[1]

Does fish oil inflame or protect the stomach?

• Human data: In a small human study, taking fish oil for several weeks did not worsen aspirin‑related reductions in stomach prostaglandins or increase visible stomach injury compared with olive oil, suggesting fish oil did not aggravate aspirin‑induced gastric damage. ^[5]
• Animal data: In rat models, fish oil reduced the extent of alcohol‑ and drug‑induced gastric injury and showed anti‑ulcer properties, although animal results don’t always translate directly to people. ^{[6] [7]}
• Overall implication: While more robust human trials are needed, available evidence does not show fish oil causes gastritis and even suggests potential protective effects in experimental settings. ^{[5] [7]}

Who might feel worse with fish or fish oil?

• Sensitive stomachs: Individuals prone to reflux or dyspepsia may feel more heartburn or nausea with fish oil, especially if they take large capsules, ingest them on an empty stomach, or use high doses. ^[1]
• Active ulcers or high bleeding risk: Because high‑dose fish oil can increase bleeding tendency, people with bleeding ulcers or those on anticoagulants should discuss dosing with a clinician, even though this is a bleeding risk issue rather than gastritis per se. ^[1]
• Seafood allergy uncertainty: Safety in seafood allergy is unclear; medical supervision is advised if allergy is suspected. ^[1]

Practical tips to minimize stomach symptoms

• Take with food: Swallow fish oil capsules with meals to reduce reflux and nausea. ^[1]
• Start low, go slow: Begin with a low dose and increase gradually if needed; many people do well at standard doses without symptoms. ^[1]
• Choose formulation wisely: Enteric‑coated or smaller capsules, or triglyceride‑based products, may lessen aftertaste and burping for some users. ^{[3] [4]}
• Consider dietary fish: Getting omega‑3s by eating baked or broiled fish can provide benefits with fewer supplement‑related GI side effects. ^[8]

When to seek medical advice

• Persistent or severe symptoms: Ongoing upper‑abdominal pain, black stools, vomiting blood, or unexplained weight loss warrant prompt evaluation for gastritis, ulcers, or other conditions. ^[2]
• Medication interactions or bleeding: If you take blood thinners or have a history of ulcers, review fish oil dosing with your clinician first. ^[1]

Bottom line

• Fish and fish oil supplements do not typically cause or worsen gastritis, although they can trigger mild GI symptoms like heartburn or nausea in some people, especially at higher doses or on an empty stomach. ^[1]
• Current evidence including a human study and several animal studies does not show fish oil increases gastric injury and even suggests possible protective effects in experimental models. ^{[5] [7]}
• If you experience stomach discomfort, adjusting dose, timing with meals, or formulation often helps; consider focusing on omega‑3‑rich fish as an alternative. ^{[1] [8]}

Quick comparison

Topic	Typical effect	Notes
Fish oil and gastritis	Unlikely to cause/worsen true gastritis	May cause mild heartburn/nausea; usually dose‑related. [1]
Bleeding risk	Possible at high doses	Relevant for ulcers/anticoagulants; discuss with clinician. [1]
Human evidence on gastric injury	No increase seen with aspirin challenge	Fish oil did not worsen aspirin‑induced gastric damage. [5]
Animal evidence	Often protective	Reduced drug/alcohol‑induced gastric injury in rats. [6] [7]
Alternatives	Eat omega‑3‑rich fish	Baked/broiled fish provides omega‑3s with fewer GI side effects. [8]

If you’re unsure whether your symptoms are from gastritis versus reflux or dyspepsia, a healthcare professional can help evaluate and tailor your omega‑3 plan while keeping your stomach comfortable.