Fish oil pills are widely used dietary supplements in the UK, valued primarily for their omega-3 polyunsaturated fatty acids—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Whilst the NHS recommends consuming oily fish regularly, many people turn to supplements when dietary intake is insufficient. Fish oil pills may support cardiovascular health, particularly in managing elevated triglycerides, and play roles in brain function and inflammatory conditions. However, evidence varies across different health claims, and not everyone requires supplementation. Understanding what fish oil pills are good for, who might benefit, and how to use them safely is essential for making informed decisions about their place in your health regimen.

What Are Fish Oil Pills and What Do They Contain?

Fish oil pills are dietary supplements derived from the tissues of oily fish, including mackerel, herring, sardines, salmon, and anchovies. These supplements are widely available over the counter in the UK and are primarily valued for their high content of omega-3 polyunsaturated fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). While the body can synthesise limited amounts of EPA and DHA from alpha-linolenic acid (ALA), this conversion is inefficient, making dietary sources particularly important.

The concentration of EPA and DHA varies considerably between products. Standard fish oil supplements typically contain between 180–300 mg of EPA and 120–200 mg of DHA per capsule, whilst prescription-strength preparations may provide significantly higher doses. Some high-dose omega-3 products are licensed medicines in the UK, including omega-3-acid ethyl esters and icosapent ethyl. The Medicines and Healthcare products Regulatory Agency (MHRA) regulates high-dose omega-3 preparations as medicines, whilst lower-dose products are classified as food supplements.

Fish oil capsules are usually presented as soft gel capsules containing liquid oil, though some manufacturers offer flavoured liquid formulations. Many products undergo molecular distillation or other purification processes to remove environmental contaminants such as mercury, polychlorinated biphenyls (PCBs), and dioxins. Quality assurance is important — reputable manufacturers provide certificates of analysis confirming purity and potency through independent third-party testing.

Some preparations combine fish oil with vitamin D or vitamin E, the latter often added as an antioxidant to prevent rancidity. Vegetarian alternatives derived from algae are available for those who prefer plant-based sources. While many algal supplements traditionally contained primarily DHA, some newer products now offer both EPA and DHA. When selecting a fish oil supplement, consumers should check the actual EPA and DHA content rather than the total fish oil amount, as this provides a more accurate indication of therapeutic potential.

Health Benefits of Fish Oil Supplements

The cardiovascular benefits of omega-3 fatty acids have been extensively researched, though evidence quality varies across different conditions. EPA and DHA contribute to normal heart function by influencing several physiological mechanisms, including reducing triglyceride levels, modestly lowering blood pressure, and potentially reducing platelet aggregation. The European Food Safety Authority (EFSA) has approved health claims stating that EPA and DHA contribute to the normal function of the heart at daily intakes of 250 mg combined.

For individuals with elevated triglycerides (hypertriglyceridaemia), high-dose prescription omega-3 preparations have demonstrated clinically significant reductions in triglyceride levels, typically in the range of 20–30%. NICE guidance acknowledges the role of omega-3 fatty acids in managing severe hypertriglyceridaemia, particularly when dietary modification and other lipid-lowering therapies have proven insufficient. However, it's important to note that NICE does not recommend standard omega-3 supplements for primary or secondary prevention of cardiovascular disease. Icosapent ethyl (a prescription-only EPA preparation) may be offered to certain high-risk patients with raised triglycerides despite statin therapy, in line with NICE Technology Appraisal 805.

Omega-3 fatty acids play structural and functional roles in the brain and retina. DHA is particularly concentrated in neural tissues and is important for brain development during pregnancy and infancy. Some observational studies suggest associations between higher omega-3 intake and reduced risk of cognitive decline, though intervention trials have not consistently demonstrated cognitive benefits in older adults without pre-existing deficiency.

Evidence for omega-3 supplementation in inflammatory conditions such as rheumatoid arthritis shows modest benefits, with some patients experiencing reduced joint pain and stiffness, potentially allowing reduced use of NSAIDs. Benefits typically take several months to develop and are generally small. The anti-inflammatory properties of EPA and DHA result from their conversion to specialised mediators that help regulate immune responses. However, fish oil should complement rather than replace conventional disease-modifying treatments. For other conditions including depression, dry eye syndrome, and pregnancy outcomes, evidence remains inconclusive, and there is no official link established for many purported benefits circulating in popular media.

Who Should Consider Taking Fish Oil Pills?

The NHS recommends that most people should aim to consume at least two portions of fish per week, including one portion of oily fish. A typical 140g portion of oily fish can provide approximately 1-3g or more of EPA and DHA, depending on the species. However, certain groups may benefit from fish oil supplementation when dietary intake is insufficient or when higher doses are therapeutically indicated.

Individuals with confirmed hypertriglyceridaemia may be prescribed high-dose omega-3 preparations (typically 2–4 g of EPA/DHA daily) under medical supervision. This is particularly relevant for those with triglyceride levels above 10 mmol/L, where there is significant risk of acute pancreatitis. Such treatment should be initiated and monitored by a GP or specialist, as it requires integration with other cardiovascular risk management strategies, including fibrates and dietary modification. For selected high-risk patients with established cardiovascular disease and raised triglycerides despite statin therapy, icosapent ethyl may be prescribed in accordance with NICE guidance.

People who do not consume fish due to dietary preferences, allergies, or cultural reasons may consider supplementation to ensure adequate omega-3 intake. Vegetarians and vegans can opt for algae-based omega-3 supplements. Pregnant and breastfeeding women should ensure adequate DHA intake for foetal and infant neurodevelopment, though they should avoid fish liver oil supplements (such as cod liver oil) due to high vitamin A content, which may be harmful during pregnancy. The NHS advises pregnant women to limit oily fish consumption to no more than two portions per week and to avoid certain fish with higher mercury levels (shark, swordfish, marlin). Standard fish oil or algae-based DHA supplements are considered safe during pregnancy.

Patients with inflammatory joint conditions such as rheumatoid arthritis may experience modest symptomatic benefit from fish oil supplementation, typically requiring doses of 2–3 g EPA/DHA daily. However, this should be discussed with a rheumatologist or GP, as benefits are generally modest and take several months to manifest.

Conversely, fish oil supplementation is not routinely recommended for the general population without specific indications. Those with adequate dietary fish intake, individuals taking anticoagulant medications (without medical advice), and people with fish or shellfish allergies should exercise caution. Anyone considering supplementation should discuss this with their GP or a registered dietitian, particularly if they have existing health conditions or take regular medications.

How to Take Fish Oil Supplements Safely

When initiating fish oil supplementation, it is advisable to start with standard doses and increase gradually if higher doses are required. For general health maintenance, doses providing at least 250 mg combined EPA and DHA daily align with the permitted health claim for contributing to normal heart function. For specific therapeutic purposes, such as triglyceride reduction, doses of 2–4 g daily may be prescribed, but such high doses should only be taken under medical supervision and not exceeded unless advised by a clinician.

Fish oil capsules are best taken with meals to enhance absorption and reduce the likelihood of gastrointestinal side effects such as reflux or fishy aftertaste. Some individuals find that taking supplements with the largest meal of the day, or freezing capsules before consumption, minimises these effects. Dividing the daily dose across multiple meals can also improve tolerability.

Quality and storage considerations are important for maintaining supplement efficacy and safety. Fish oil is susceptible to oxidation, which produces rancid odours and potentially harmful compounds. Supplements should be stored in a cool, dark place, and bottles should be tightly sealed after use. Refrigeration can extend shelf life. Check expiry dates and discard any supplements that smell unpleasant or appear discoloured.

When selecting a product, look for supplements that have been independently tested for purity and potency. In the UK, products with third-party certification provide additional assurance regarding contaminant levels and label accuracy. Read labels carefully to determine actual EPA and DHA content rather than total fish oil content.

Patients taking anticoagulant or antiplatelet medications (such as warfarin, apixaban, or clopidogrel) should consult their GP before starting fish oil supplements, as omega-3 fatty acids possess mild antiplatelet effects that could theoretically increase bleeding risk, particularly at high doses. Any changes to fish oil intake while on warfarin should be coordinated with the anticoagulation clinic or GP to monitor INR as needed. Similarly, individuals scheduled for surgery should inform their surgical team about fish oil supplementation. Those with diabetes should be aware that high-dose fish oil generally has neutral effects on blood glucose control, though monitoring may be appropriate when initiating treatment if clinically indicated.

Potential Side Effects and Interactions

Fish oil supplements are generally well tolerated, but some individuals experience mild gastrointestinal side effects. The most commonly reported adverse effects include:

• Fishy aftertaste or reflux — often described as 'fish burps'

• Nausea or mild stomach upset

• Loose stools or diarrhoea, particularly with higher doses

• Fishy body odour in some individuals taking high doses

These effects are usually dose-dependent and can often be minimised by taking supplements with food, choosing enteric-coated formulations, or reducing the dose. If gastrointestinal symptoms persist or worsen, discontinue use and consult a healthcare professional.

High-dose prescription omega-3 preparations have been associated with a small increased risk of atrial fibrillation in some studies. Seek medical advice if you notice palpitations or irregular heartbeat while taking these supplements.

Allergic reactions to fish oil supplements are uncommon but possible, particularly in individuals with fish allergies. Symptoms may include rash, itching, swelling, or difficulty breathing. Anyone experiencing signs of an allergic reaction should stop taking the supplement immediately and seek medical attention. If you experience severe symptoms such as difficulty breathing, swelling of the face/throat, or feel faint, call 999 immediately. It is worth noting that fish oil is derived from fish tissue rather than shellfish, so individuals with shellfish allergies may tolerate fish oil, though caution is advised.

Regarding drug interactions, the most clinically significant concern involves anticoagulant and antiplatelet medications. Whilst fish oil possesses mild antiplatelet properties, clinically significant bleeding complications are rare at standard supplemental doses. Nevertheless, patients taking warfarin should have their INR monitored if initiating or discontinuing fish oil supplementation. Theoretical interactions exist with blood pressure medications, as omega-3 fatty acids may have modest hypotensive effects, though this is rarely problematic in practice.

High-dose omega-3-acid ethyl esters may slightly increase LDL cholesterol in some individuals, though this effect is inconsistent and generally outweighed by triglyceride-lowering benefits when prescribed for hypertriglyceridaemia. Pure EPA (icosapent ethyl) typically does not raise LDL. Patients should have lipid profiles monitored appropriately.

When to contact your GP:

• Persistent gastrointestinal symptoms

• Signs of allergic reaction

• Unusual bleeding or bruising

• Palpitations or irregular heartbeat

• If you are taking anticoagulants or have a bleeding disorder

• Before taking high doses (above 1 g EPA/DHA daily)

Pregnant women, individuals with liver disease, and those with compromised immune systems should discuss supplementation with their healthcare provider before commencing treatment. If you experience any suspected side effects from fish oil supplements, you can report them through the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Frequently Asked Questions