EPA and DHA supplements provide concentrated forms of essential omega-3 fatty acids that support cardiovascular, brain, and eye health. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are long-chain polyunsaturated fatty acids primarily obtained from oily fish or algal sources. Whilst the body can convert plant-based omega-3s into EPA and DHA, this process is highly inefficient, making dietary intake or supplementation important for many individuals. In the UK, most omega-3 products are regulated as food supplements, though high-strength preparations for specific medical conditions require a prescription. Understanding the evidence, appropriate dosing, and quality considerations helps ensure safe and effective use of these widely available supplements.

What Are EPA and DHA Supplements?

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are long-chain omega-3 polyunsaturated fatty acids that play essential roles in human health. These fatty acids are primarily found in marine sources, particularly oily fish such as salmon, mackerel, sardines, and herring. EPA and DHA supplements are concentrated preparations of these omega-3 fatty acids, typically derived from fish oil, krill oil, or algal oil for vegetarian and vegan formulations.

The human body has limited capacity to synthesise EPA and DHA from the plant-based omega-3 fatty acid alpha-linolenic acid (ALA), with conversion rates typically around 5-10% for EPA and only about 1-5% for DHA. This inefficient conversion means that dietary intake or supplementation becomes the primary route for obtaining adequate levels of these important fatty acids. EPA and DHA have distinct but complementary biological functions: EPA is particularly involved in anti-inflammatory processes and cardiovascular health, whilst DHA is a major structural component of brain tissue, the retina, and cell membranes throughout the body.

Common supplement formulations include:

• Fish oil capsules – the most widely available form, containing varying ratios of EPA to DHA

• Concentrated omega-3 preparations – higher purity products with standardised doses

• Algal oil supplements – plant-based alternatives suitable for vegetarians and vegans

• Krill oil – contains EPA and DHA bound to phospholipids, though evidence for enhanced absorption is mixed and clinical significance unclear

In the UK, most EPA and DHA products are regulated as food supplements. However, products making medicinal claims or presented as treating or preventing disease are classified as medicines and regulated by the Medicines and Healthcare products Regulatory Agency (MHRA). This classification depends on the product's presentation and function, not simply its dose. Some high-strength omega-3 preparations are available only on prescription for specific medical conditions.

Health Benefits of EPA and DHA

EPA and DHA have been extensively studied for their health effects. These omega-3 fatty acids can help reduce triglyceride levels, modestly lower blood pressure, and have anti-inflammatory properties. The mechanism involves multiple pathways: EPA and DHA reduce hepatic triglyceride synthesis, improve endothelial function, and may help modulate inflammatory responses. However, it's important to note that NICE does not recommend routine omega-3 supplements for primary or secondary prevention of cardiovascular disease. Only prescription icosapent ethyl (a highly purified EPA) is recommended for specific high-risk adults with elevated triglycerides and established cardiovascular disease or diabetes (NICE TA805).

DHA is critically important for brain health and cognitive function throughout the lifespan. It comprises approximately 40% of polyunsaturated fatty acids in the brain and 60% in the retina. During pregnancy and early childhood, adequate DHA intake supports foetal and infant neurodevelopment, with some studies suggesting improved visual and cognitive outcomes, though evidence is mixed. In adults, while observational studies suggest associations between omega-3 intake and cognitive health, intervention trials have shown inconsistent results.

Additional evidence for omega-3 fatty acids includes:

• Anti-inflammatory effects – EPA and DHA produce specialised pro-resolving mediators (resolvins and protectins) that help resolve inflammation

• Mental health – some evidence suggests EPA-predominant formulations may have modest benefits in depression as adjunctive therapy, though not routinely recommended by NICE

• Eye health – DHA maintains retinal structure and function, though evidence for supplementation preventing age-related macular degeneration is inconclusive

• Joint health – may help reduce morning stiffness and pain in rheumatoid arthritis as an adjunct to standard treatments

It is important to note that whilst associations exist between omega-3 intake and various health outcomes, the evidence strength varies considerably, and individual responses differ. Many potential benefits require further research to establish definitive recommendations.

Who Should Consider EPA and DHA Supplements?

The Scientific Advisory Committee on Nutrition (SACN) recommends that adults consume at least 450 mg of combined EPA and DHA daily, primarily through dietary sources such as oily fish. This equates to about one to two portions of oily fish weekly. While a 'food first' approach is preferred, some individuals may consider supplements if they cannot meet these recommendations through diet alone.

Those following vegetarian or vegan diets face particular challenges, as plant-based omega-3 sources provide only ALA, which converts poorly to EPA and DHA. Algal oil supplements offer a suitable alternative for these individuals.

Pregnant and breastfeeding women have increased requirements for DHA to support foetal brain and eye development. The NHS advises pregnant women to consume oily fish but limit intake to two portions weekly due to potential contaminant concerns. While DHA supplements (typically around 200 mg daily) are considered safe during pregnancy, they are not routinely recommended by the NHS for all pregnant women. Importantly, pregnant women should avoid cod liver oil supplements due to their high vitamin A content, which may harm the developing baby. Women should consult their midwife or GP before starting any supplements during pregnancy.

Other groups who might discuss supplementation with healthcare professionals include:

• Individuals with very high triglycerides – prescription omega-3 products may be used under medical supervision

• Specific high-risk cardiovascular patients – prescription icosapent ethyl is recommended only for defined groups (NICE TA805)

• People with inflammatory conditions – such as rheumatoid arthritis, as a possible adjunct to standard treatments

• Those with limited fish consumption – due to dietary preferences, allergies, or availability

Patients taking anticoagulant medications (warfarin, DOACs) or antiplatelet drugs should discuss supplementation with their GP or pharmacist, as high-dose omega-3 fatty acids may theoretically increase bleeding risk. Similarly, individuals with fish or shellfish allergies should exercise caution and may require algal-based alternatives.

Dosage and How to Take EPA and DHA Supplements

The optimal dosage of EPA and DHA varies according to the intended purpose and individual circumstances. For general health maintenance in adults, the SACN recommends a minimum of 450 mg combined EPA and DHA daily, which can typically be achieved through one to two portions of oily fish weekly. For those using supplements to meet this recommendation, products providing 250–500 mg daily of combined EPA and DHA are commonly available.

For specific medical conditions, different dosages may be used under healthcare professional supervision:

Dosage contexts:

• Severe hypertriglyceridaemia – prescription omega-3-acid ethyl esters (e.g., Omacor) at 2-4 g daily

• Cardiovascular risk reduction – prescription icosapent ethyl (Vazkepa) 2 g twice daily in specific high-risk patients (NICE TA805)

• Pregnancy and lactation – if supplementing, typically around 200 mg DHA daily

• Research settings – various doses have been studied for conditions like depression (1,000–2,000 mg EPA) and rheumatoid arthritis (2,000–3,000 mg combined EPA and DHA), but these are not standard NHS recommendations

EPA and DHA supplements are fat-soluble and absorption is enhanced when taken with meals containing dietary fat. Taking supplements with breakfast or the largest meal of the day typically optimises absorption and may reduce gastrointestinal side effects such as fishy aftertaste or reflux. Some individuals find that refrigerating capsules or taking them frozen reduces these effects.

The ratio of EPA to DHA varies between products. Fish oil supplements typically contain both in varying proportions, whilst algal oils may be DHA-predominant. The European Food Safety Authority (EFSA) considers combined EPA and DHA intakes up to 5 g daily to be generally safe for adults.

Consistency in supplementation is important, as tissue levels of omega-3 fatty acids build gradually over weeks to months. Patients should inform their GP about supplement use, particularly before surgery or if taking anticoagulants, as monitoring may be advised when initiating supplements.

Side Effects and Safety Considerations

EPA and DHA supplements are generally well tolerated at recommended doses, with most adverse effects being mild and gastrointestinal in nature. The most commonly reported side effects include fishy aftertaste, belching, nausea, and loose stools. These effects are typically dose-dependent and can often be minimised by taking supplements with meals, choosing enteric-coated formulations, or refrigerating capsules. Some individuals find that starting with lower doses and gradually increasing helps improve tolerance.

At higher doses (above 3,000 mg daily), there is theoretical concern about increased bleeding risk due to the antiplatelet effects of omega-3 fatty acids. However, clinical evidence suggests that this risk is minimal at typical supplementation doses, and serious bleeding complications are rare. Nevertheless, patients taking anticoagulants (warfarin, apixaban, rivaroxaban) or antiplatelet medications (aspirin, clopidogrel) should discuss supplementation with their GP or anticoagulation clinic. Routine monitoring of INR may be advisable when initiating high-dose omega-3 supplementation in patients on warfarin.

High-dose prescription omega-3 products, particularly purified EPA (icosapent ethyl), have been associated with an increased risk of atrial fibrillation in clinical trials. Patients should seek medical advice if they experience palpitations or irregular heartbeat.

Important safety considerations include:

• Allergic reactions – individuals with fish or shellfish allergies should exercise caution; algal oil provides a suitable alternative

• Contaminants – lower-quality fish oils may contain environmental pollutants such as mercury, PCBs, or dioxins

• Drug interactions – potential interactions with blood pressure medications, though clinically significant effects are uncommon

• Vitamin A and D toxicity – cod liver oil supplements contain these fat-soluble vitamins and excessive intake should be avoided

When to contact your GP:

• Persistent gastrointestinal symptoms that don't resolve with dose adjustment

• Unusual bruising or bleeding whilst taking omega-3 supplements

• Palpitations or irregular heartbeat

• Before starting supplements if you have a bleeding disorder or are scheduled for surgery

• If you experience allergic symptoms such as rash, swelling, or difficulty breathing

Pregnant women should avoid cod liver oil due to high vitamin A content, which may harm the developing baby. Standard fish oil or algal oil supplements are considered safer alternatives during pregnancy.

If you experience any suspected side effects from supplements, you can report them through the MHRA Yellow Card Scheme.

Choosing Quality EPA and DHA Supplements in the UK

The quality and purity of EPA and DHA supplements vary considerably between products available in the UK market. When selecting a supplement, consumers should look for products that have undergone third-party testing for purity, potency, and absence of contaminants. Reputable manufacturers typically provide certificates of analysis confirming that their products meet quality standards and are free from heavy metals, PCBs, and other environmental pollutants.

Key quality indicators include:

• Purity and concentration – check the actual EPA and DHA content per capsule, not just total fish oil content

• Form of omega-3 – some evidence suggests triglyceride or re-esterified triglyceride forms may have different absorption characteristics than ethyl ester forms, though the clinical significance of these differences is uncertain

• Third-party certification – look for products certified by organisations such as IFOS (International Fish Oil Standards) or approved by Informed-Sport for athletes

• Freshness – omega-3 fatty acids are susceptible to oxidation; check expiry dates and avoid products with rancid odour

In the UK, products making medicinal claims or presented as treating or preventing disease are regulated as medicines by the MHRA, regardless of their dose. Prescription omega-3 preparations (such as omega-3-acid ethyl esters and icosapent ethyl) are licensed medicines with specific indications and contain standardised doses. These products undergo rigorous quality control but require a prescription and are typically reserved for therapeutic use.

For over-the-counter supplements, consumers should purchase from reputable retailers and established brands. The label should clearly state the amounts of EPA and DHA per serving, not just total omega-3 content. Sustainable sourcing is another consideration; look for products certified by the Marine Stewardship Council (MSC) or similar organisations that ensure responsible fishing practices.

Practical purchasing advice:

• Compare EPA and DHA content per capsule to determine value, as capsule size doesn't always reflect omega-3 content

• Consider your dietary preferences – algal oil for vegetarians/vegans, krill oil for those seeking phospholipid-bound omega-3s

• Store supplements in a cool, dark place and refrigerate after opening to prevent oxidation

• Be wary of exaggerated health claims; legitimate products focus on evidence-based benefits

Patients uncertain about which supplement to choose should consult their community pharmacist, who can provide guidance on appropriate products and dosing for individual circumstances.

Frequently Asked Questions