Fish oil supplements, rich in omega-3 fatty acids EPA and DHA, are widely used to support cardiovascular and brain health. Whilst there is no single optimal time to take fish oil, consistency and taking it with meals can enhance absorption and reduce side effects. Understanding when to take fish oil, appropriate dosing, and potential interactions is essential for safe and effective use. This article provides evidence-based guidance on timing, dosage, and safety considerations for fish oil supplementation in line with UK clinical recommendations, helping you make informed decisions about incorporating omega-3s into your daily routine.

What Is Fish Oil and Why Take It?

Fish oil is a dietary supplement derived from the tissues of oily fish such as mackerel, salmon, sardines, and anchovies. It is rich in omega-3 polyunsaturated fatty acids, primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These essential fatty acids cannot be synthesised efficiently by the human body and must therefore be obtained through diet or supplementation.

Omega-3 fatty acids play important roles in normal body functions including cardiovascular health, brain function, and various physiological processes. At a daily intake of 250 mg, EPA and DHA contribute to normal heart function according to the GB Nutrition and Health Claims Register. DHA (at 250 mg daily) contributes to the maintenance of normal brain function and vision. However, it's important to note that NICE does not recommend routine omega-3 supplements for the prevention of cardiovascular disease.

Many people in the UK do not consume sufficient oily fish to meet recommended intake levels. The NHS advises eating at least two portions of fish per week, including one portion of oily fish (approximately 140g). For those who do not regularly consume fish—whether due to dietary preferences, allergies, or lifestyle factors—fish oil supplements offer a convenient alternative to help maintain adequate omega-3 intake.

Whilst fish oil supplements are widely available over the counter, it is important to recognise that they are not a substitute for a varied, balanced diet. There is a distinction between over-the-counter supplements and prescription omega-3 products (such as icosapent ethyl or omega-3 acid ethyl esters), which are licensed for specific medical conditions. Individuals considering supplementation should be aware of appropriate dosing, timing, and potential interactions with medications, particularly anticoagulants. Those with specific health conditions should consult their GP or a registered dietitian before commencing supplementation.

When to Take Fish Oil: Morning, Evening or With Meals

There is no definitive clinical evidence establishing a single optimal time of day to take fish oil supplements. The most important factor is consistency—taking your supplement at the same time each day helps establish a routine and ensures regular intake. However, several practical considerations may influence when you choose to take fish oil.

Taking fish oil with meals is generally recommended for several reasons. Omega-3 fatty acids are fat-soluble, meaning they are better absorbed when consumed alongside dietary fats. A meal containing some fat—even a modest amount—can enhance the bioavailability of EPA and DHA, ensuring your body absorbs these nutrients more efficiently. Additionally, taking fish oil with food may help reduce common gastrointestinal side effects such as fishy aftertaste, reflux, or mild nausea.

Some individuals prefer taking fish oil in the morning with breakfast, as this fits naturally into their daily routine and may reduce the likelihood of experiencing reflux or aftertaste during the day. Others find that taking it with their evening meal works better, particularly if they experience any mild digestive discomfort, as lying down shortly after taking supplements can sometimes exacerbate reflux symptoms.

If you are taking fish oil for specific health reasons, splitting the dose between morning and evening meals may provide more stable blood levels of omega-3 fatty acids throughout the day, though this is optional and there is no evidence it improves clinical outcomes. For prescription omega-3 products (such as icosapent ethyl or omega-3 acid ethyl esters), you should follow the specific instructions in the patient information leaflet, which typically advise taking with food.

Ultimately, the best time to take fish oil is whenever you are most likely to remember and maintain consistent use. If you experience persistent digestive upset regardless of timing, consider trying a different formulation (such as enteric-coated capsules) or discussing alternatives with your pharmacist or GP.

How Much Fish Oil Should You Take Daily?

The appropriate daily dose of fish oil depends on several factors, including your age, overall health status, dietary omega-3 intake, and the specific reason for supplementation. There is no single universally recommended dose, but general guidance can help inform safe and effective use.

For general health maintenance in adults, many supplements provide between 250–500 mg of combined EPA and DHA per day. This aligns broadly with recommendations to consume oily fish regularly. The GB Nutrition and Health Claims Register indicates that consuming 250 mg of EPA and DHA daily contributes to normal heart function. However, it's important to note that NICE does not recommend routine omega-3 supplements for the prevention of cardiovascular disease.

It is crucial to distinguish between the total amount of fish oil in a capsule and the actual EPA and DHA content. A 1,000 mg fish oil capsule may contain only 300 mg of omega-3 fatty acids, so always check the label for the specific EPA and DHA quantities. Reputable supplements will clearly state these amounts.

For specific clinical indications—such as hypertriglyceridaemia (elevated blood triglycerides)—prescription-strength omega-3 preparations may be prescribed under medical supervision. These include omega-3 acid ethyl esters (e.g., Omacor) and icosapent ethyl (Vazkepa), which differ from over-the-counter supplements in their purity, concentration, and regulatory status. NICE guidance recommends icosapent ethyl (typically 2g twice daily) only for specific high-risk populations with elevated triglycerides despite statin therapy.

The European Food Safety Authority considers intakes up to 5g per day of EPA and DHA combined to be generally safe for adults, but the risk of bleeding and other side effects increases at higher doses. Seek medical advice if considering doses above 2g per day.

Pregnant and breastfeeding women may benefit from omega-3 supplementation, particularly DHA, which supports foetal brain and eye development. However, it is essential to choose supplements specifically formulated for pregnancy, avoiding those with vitamin A content (such as cod liver oil), and to consult a midwife or GP before starting supplementation. Children's doses vary by age and should follow manufacturer guidance or professional advice.

Potential Side Effects and Who Should Avoid Fish Oil

Fish oil supplements are generally well tolerated, but some individuals may experience mild side effects, particularly when first starting supplementation or taking higher doses. Common adverse effects include:

• Gastrointestinal symptoms: fishy aftertaste, belching, nausea, loose stools, or mild indigestion

• Fishy breath or body odour: occasionally reported with higher doses

• Mild bleeding tendency: omega-3 fatty acids have antiplatelet effects, which may slightly prolong bleeding time

These effects are usually mild and can often be minimised by taking fish oil with meals, choosing enteric-coated formulations, or refrigerating capsules. If gastrointestinal symptoms persist or worsen, discontinue use and consult your GP or pharmacist.

Certain individuals should exercise caution or avoid fish oil without medical guidance. Those taking anticoagulant or antiplatelet medications (such as warfarin, apixaban, clopidogrel, or aspirin) should consult their GP before using fish oil, as the combination may increase bleeding risk. Patients on warfarin should consider INR monitoring when starting or changing fish oil doses. Similarly, individuals with bleeding disorders or those scheduled for surgery should discuss supplementation with their healthcare team, as fish oil may need to be discontinued prior to procedures.

High-dose prescription omega-3 products (such as icosapent ethyl) have been associated with an increased risk of atrial fibrillation. Seek medical advice if you experience palpitations or irregular heartbeat while taking omega-3 supplements.

People with fish or seafood allergies should avoid fish oil supplements and consider algae-based omega-3 alternatives, which provide EPA and DHA without fish-derived ingredients. Those with diabetes should monitor blood glucose levels, as high-dose fish oil may slightly affect glycaemic control in some individuals, though evidence is inconsistent.

When to contact your GP: Seek medical advice if you experience unusual bruising, prolonged bleeding from minor cuts, black or tarry stools, severe abdominal pain, or allergic reactions (rash, swelling, difficulty breathing). Always inform your GP and pharmacist about all supplements you are taking, as these can interact with prescribed medications. Fish oil should complement, not replace, evidence-based treatments for cardiovascular or other health conditions.

Report any suspected side effects to the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).

Frequently Asked Questions