Are fish oil pills good for you? The answer depends on your individual circumstances and dietary habits. Fish oil supplements contain omega-3 polyunsaturated fatty acids—primarily EPA and DHA—which play important roles in cardiovascular health, brain function, and inflammation. Whilst eating oily fish is recommended by the NHS, supplements may benefit those who do not consume adequate amounts through diet. However, evidence for routine supplementation in preventing heart disease is less compelling than once thought. This article examines the composition, benefits, risks, and appropriate use of fish oil supplements within the context of UK clinical guidance.

What Are Fish Oil Pills and What Do They Contain?

Fish oil supplements are derived from the tissues of oily fish species, including mackerel, herring, sardines, anchovies, and salmon. These capsules contain concentrated amounts of omega-3 polyunsaturated fatty acids, primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are derived from alpha-linolenic acid (ALA), which is the essential omega-3 fatty acid. The human body converts ALA to EPA and DHA, but this conversion is inefficient, making dietary sources or supplements valuable.

A typical fish oil capsule contains between 180–500 mg of combined EPA and DHA, though high-strength preparations may provide up to 1,000 mg per capsule. The remaining content consists of other fatty acids, vitamin E (added as an antioxidant to prevent rancidity), and the capsule shell itself, usually made from gelatin or plant-based alternatives.

It's important to distinguish between fish body oil supplements and fish liver oil supplements (such as cod liver oil). Fish liver oils naturally contain vitamins A and D, which may be beneficial but require careful dosing, particularly during pregnancy.

The quality and purity of fish oil supplements can vary considerably between manufacturers. Reputable products undergo molecular distillation or other purification processes to remove environmental contaminants such as mercury, polychlorinated biphenyls (PCBs), and dioxins. The concentration of EPA and DHA, the form of omega-3 (triglyceride, ethyl ester, or phospholipid), and the presence of additional ingredients may affect the supplement's absorption, though the clinical significance of these differences remains uncertain.

Key components of fish oil supplements:

• EPA (eicosapentaenoic acid) – typically 180–360 mg per standard capsule

• DHA (docosahexaenoic acid) – typically 120–240 mg per standard capsule

• Vitamin E – added as a preservative

• Other omega-3 and omega-6 fatty acids – in smaller quantities

Health Benefits of Fish Oil Supplements: What the Evidence Shows

The cardiovascular benefits of omega-3 fatty acids have been extensively studied, though the evidence base presents a nuanced picture. EPA and DHA exert anti-inflammatory effects, reduce triglyceride levels, and may modestly lower blood pressure. In the UK, prescription omega-3-acid ethyl esters are licensed for the treatment of hypertriglyceridaemia, while icosapent ethyl (a purified EPA product) is recommended by NICE (TA805) for cardiovascular risk reduction in selected high-risk adults already taking statins.

However, NICE guidance (NG238) does not recommend routine omega-3 supplementation for primary or secondary prevention of cardiovascular disease in most individuals. While eating oily fish is associated with cardiovascular benefits, the evidence for over-the-counter fish oil supplements in preventing heart disease is less compelling.

It's worth noting that high-dose prescription omega-3 products have been associated with an increased risk of atrial fibrillation in some studies, particularly with icosapent ethyl. This highlights the importance of medical supervision when using higher doses.

Beyond cardiovascular health, omega-3 fatty acids play crucial roles in brain function and development. DHA is a major structural component of neuronal membranes and retinal tissue. Some evidence suggests that adequate omega-3 intake during pregnancy may support foetal neurodevelopment, though supplementation trials have shown inconsistent results. Research into omega-3 supplementation for cognitive decline, depression, and inflammatory conditions such as rheumatoid arthritis has produced promising but not conclusive findings.

Conditions with evidence of potential benefit:

• Hypertriglyceridaemia – prescription-strength preparations can reduce triglyceride levels by 20–30%

• Rheumatoid arthritis – may reduce joint pain and stiffness as adjunctive therapy

• Dry eye syndrome – evidence is mixed, with some large trials showing no benefit over placebo

• Pregnancy – supports foetal brain and eye development, though evidence for routine supplementation is inconsistent

It is important to note that fish oil supplements should not replace prescribed medications or a balanced diet rich in oily fish, which provides additional nutrients and health benefits beyond isolated omega-3 fatty acids.

Who Should Consider Taking Fish Oil Pills?

Fish oil supplementation may be appropriate for individuals who do not consume adequate amounts of oily fish through their diet. The NHS recommends eating at least one portion (approximately 140 g) of oily fish per week, which provides sufficient omega-3 fatty acids for most healthy adults. Those who do not meet this dietary recommendation due to personal preference, dietary restrictions, or limited access to fresh fish may consider supplementation.

Pregnant and breastfeeding women represent a specific group who may consider omega-3 supplementation, as DHA is important for foetal and infant brain development. However, the NHS advises pregnant and breastfeeding women to limit oily fish consumption to no more than two portions per week and to avoid shark, swordfish, and marlin completely due to potential mercury contamination. Pregnant women should also avoid supplements derived from fish liver (such as cod liver oil) due to high vitamin A content, which can be harmful to the developing foetus. Standard fish oil or algae-based omega-3 supplements are safer alternatives. Women planning pregnancy or who are pregnant should discuss supplementation with their midwife or GP.

Individuals with confirmed hypertriglyceridaemia may be prescribed specific omega-3 medicines by their healthcare provider as part of a comprehensive lipid management strategy. It's important to note that over-the-counter supplements should not be substituted for prescription omega-3 products. Patients with inflammatory conditions such as rheumatoid arthritis sometimes use fish oil supplements as complementary therapy, though this should be discussed with a rheumatologist. Those taking anticoagulant medications require medical supervision before starting fish oil supplements due to potential interactions.

Groups who may benefit from fish oil supplementation:

• Individuals who do not eat oily fish regularly

• Pregnant and breastfeeding women (using appropriate formulations and following NHS guidance)

• People with diagnosed hypertriglyceridaemia (using prescription products under medical supervision)

• Vegetarians and vegans (using algae-based omega-3 supplements, noting these often provide more DHA than EPA)

Conversely, fish oil supplementation is generally unnecessary for those who regularly consume oily fish and maintain a balanced diet. The benefits of whole food sources extend beyond isolated nutrients and include protein, selenium, iodine, and vitamin D.

Potential Side Effects and Risks of Fish Oil Supplements

Fish oil supplements are generally well tolerated, but adverse effects can occur, particularly at higher doses. The most common side effects are gastrointestinal and include nausea, loose stools, indigestion, and a fishy aftertaste or burping. These symptoms can often be minimised by taking capsules with meals, choosing enteric-coated formulations, or refrigerating the supplements. Some individuals find that starting with a lower dose and gradually increasing helps improve tolerance.

Omega-3 fatty acids possess mild antiplatelet effects, which theoretically increase bleeding risk. Whilst clinically significant bleeding is rare, patients taking anticoagulants (such as warfarin, apixaban, or rivaroxaban) or antiplatelet agents (including aspirin or clopidogrel) should consult their GP or anticoagulation clinic before starting fish oil supplements. Any perioperative changes to supplement use should be made on the advice of the surgical or anaesthesia team. There is no official link between standard-dose fish oil supplementation and major bleeding events in most individuals, but caution is warranted in those with bleeding disorders or scheduled for surgery.

High-dose prescription omega-3 products, particularly icosapent ethyl, have been associated with an increased risk of atrial fibrillation. Individuals taking prescription omega-3 medicines should seek medical advice if they experience palpitations or irregular heartbeat. Additionally, omega-3-acid ethyl esters used for hypertriglyceridaemia may increase LDL-cholesterol levels in some patients, requiring monitoring by healthcare professionals.

Allergic reactions to fish oil supplements are uncommon but can occur in individuals with fish or shellfish allergies. Some capsules may also contain other allergens such as soya in the excipients. Symptoms may include rash, itching, swelling, or respiratory difficulties. Anyone experiencing signs of an allergic reaction should discontinue the supplement immediately and seek medical attention. Algae-based omega-3 supplements provide a suitable alternative for those with fish allergies.

Common and important adverse effects:

• Gastrointestinal disturbance – nausea, diarrhoea, fishy aftertaste (very common)

• Increased bleeding tendency – particularly relevant for those on anticoagulants (uncommon)

• Atrial fibrillation – with high-dose prescription products (uncommon)

• Allergic reactions – in individuals with fish allergy (rare)

• Vitamin A toxicity – only with cod liver oil at excessive doses (rare)

When to contact your GP:

• Unusual bruising or bleeding

• Persistent gastrointestinal symptoms

• Palpitations or irregular heartbeat (especially with high-dose products)

• Signs of allergic reaction (rash, swelling, breathing difficulties)

• If taking anticoagulant or antiplatelet medications

Patients should inform healthcare professionals about all supplements they take, as fish oil can interact with certain medications and may need to be temporarily discontinued before surgical procedures. If you experience suspected side effects from supplements or medicines, report them via the MHRA Yellow Card scheme.

How to Choose and Take Fish Oil Pills Safely

Selecting a high-quality fish oil supplement requires attention to several key factors. Look for products that clearly state the amounts of EPA and DHA per capsule, rather than just total fish oil content. Reputable manufacturers provide third-party testing certificates confirming purity and the absence of contaminants such as heavy metals, PCBs, and dioxins. Choose products that comply with UK and EU food supplement regulations, with clear labelling of ingredients and dosage.

The form of omega-3 in the supplement affects absorption. Natural triglyceride and re-esterified triglyceride forms may be better absorbed than ethyl ester forms, though the clinical significance of this difference remains uncertain. Enteric-coated capsules may reduce gastrointestinal side effects. For those following plant-based diets, algae-derived omega-3 supplements provide DHA and varying amounts of EPA without animal products and avoid concerns about marine contamination.

It's important to understand that most fish oil products are food supplements regulated by the Food Standards Agency (FSA), not medicines regulated by the MHRA. Prescription omega-3 medicines for hypertriglyceridaemia or cardiovascular risk reduction should only be used under medical supervision.

Regarding dosage, the European Food Safety Authority (EFSA) suggests that 250 mg of combined EPA and DHA daily is adequate for most healthy adults. The NHS does not specify a supplement dose but advises against exceeding 3 g of fish oil supplements daily without medical guidance due to the increased risk of bleeding. Therapeutic doses for specific conditions may be considerably higher but should only be taken under medical supervision.

Practical guidance for safe use:

• Storage – keep in a cool, dark place or refrigerate to prevent oxidation

• Timing – take with meals to enhance absorption and reduce gastrointestinal upset

• Monitoring – check expiry dates and discard capsules that smell rancid

• Interactions – inform your GP about fish oil use, especially before surgery or if taking anticoagulants

• Children – specific paediatric formulations are available; discuss with a healthcare professional

Pregnant women should choose supplements specifically formulated for pregnancy, avoiding cod liver oil due to vitamin A content. Anyone with existing medical conditions, particularly bleeding disorders, liver disease, or diabetes, should consult their GP before starting supplementation. Fish oil supplements are not suitable substitutes for prescribed medications, and individuals should not discontinue or alter prescribed treatments without medical advice.

Ultimately, whilst fish oil supplements can be beneficial for certain individuals, obtaining omega-3 fatty acids through dietary sources of oily fish remains the preferred approach for most people, providing a broader range of nutrients within the context of a balanced, healthy diet.

Frequently Asked Questions