Does fish oil lower triglycerides? Yes, omega-3 fatty acids from fish oil can effectively reduce triglyceride levels, particularly at therapeutic doses. Prescription-strength omega-3 preparations containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been shown to lower triglycerides by approximately 20–30% in individuals with moderate to severe hypertriglyceridaemia. These marine-derived fatty acids work by reducing hepatic triglyceride synthesis and enhancing clearance of triglyceride-rich lipoproteins from the bloodstream. Whilst standard over-the-counter fish oil supplements contain omega-3s, prescription formulations are generally required to achieve clinically meaningful triglyceride reduction and are supported by robust clinical evidence.

How Fish Oil Affects Triglyceride Levels

Fish oil contains omega-3 polyunsaturated fatty acids, primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which appear to influence lipid metabolism through several mechanisms. Research suggests these marine-derived fatty acids may reduce hepatic triglyceride synthesis by affecting enzymes involved in fatty acid production. This mechanism is thought to decrease the liver's capacity to manufacture very-low-density lipoprotein (VLDL) particles, which are primary carriers of triglycerides in the bloodstream.

Omega-3 fatty acids may also enhance the clearance of triglyceride-rich lipoproteins from circulation by influencing lipoprotein lipase activity, the enzyme responsible for breaking down triglycerides in blood vessels. Additionally, EPA and DHA may promote fatty acid metabolism in the liver, effectively shifting hepatic processes towards fat utilisation rather than fat storage. These combined mechanisms contribute to reductions in serum triglyceride concentrations.

The triglyceride-lowering effect of fish oil is dose-dependent, with higher intakes of EPA and DHA producing more substantial reductions. Clinical studies show that prescription-strength omega-3 preparations can reduce triglyceride levels by approximately 20-30% when used at therapeutic doses. This effect is particularly pronounced in individuals with moderate to severe hypertriglyceridaemia (triglyceride levels above 2.3 mmol/L). Importantly, whilst fish oil effectively lowers triglycerides, its impact on other lipid parameters varies, with DHA-containing products sometimes associated with modest increases in LDL cholesterol.

Evidence for Fish Oil in Lowering Triglycerides

Clinical evidence supports the use of omega-3 fatty acids for triglyceride reduction, with multiple randomised controlled trials confirming their efficacy. Systematic reviews have found that omega-3 supplementation consistently reduces triglyceride levels across diverse patient populations, with the magnitude of effect correlating with baseline triglyceride concentrations and omega-3 dosage. Patients with higher baseline triglycerides typically experience greater absolute reductions.

Prescription omega-3 preparations have undergone rigorous evaluation in large-scale cardiovascular outcome trials. The REDUCE-IT trial, which used high-dose icosapent ethyl (a purified EPA formulation, licensed in the UK as Vazkepa), demonstrated significant cardiovascular risk reduction in specific patients with elevated triglycerides despite statin therapy. Substantial triglyceride lowering (approximately 18-20% reduction) was observed. The STRENGTH trial, using a different omega-3 formulation (omega-3 carboxylic acids, not licensed in the UK), similarly showed triglyceride reductions though without the same cardiovascular benefit, highlighting that not all omega-3 products are equivalent.

In the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) has licensed Omacor (omega-3-acid ethyl esters) for treating hypertriglyceridaemia. NICE Technology Appraisal 805 recommends icosapent ethyl (Vazkepa) with statins specifically for reducing cardiovascular risk in adults with established cardiovascular disease who have raised triglycerides and controlled LDL cholesterol. It's important to note that NICE does not recommend generic omega-3 supplements for lipid management. The evidence base is strongest for prescription-strength products containing at least 2-4 grams of EPA and DHA daily, rather than standard over-the-counter fish oil supplements which contain substantially lower concentrations of active omega-3 fatty acids.

Recommended Dosage and Formulations

The dosage of omega-3 fatty acids required to achieve clinically meaningful triglyceride reduction differs substantially from amounts used for general cardiovascular health. For triglyceride lowering, therapeutic doses typically range from 2 to 4 grams of combined EPA and DHA daily, significantly higher than the 250-500 mg daily intake recommended for cardiovascular disease prevention in the general population. Standard over-the-counter fish oil supplements often contain only 300-500 mg of omega-3 per capsule, meaning multiple capsules would be required to reach therapeutic levels.

Prescription omega-3 preparations available in the UK include:

• Omacor (omega-3-acid ethyl esters): Contains 1 gram of omega-3 per capsule (approximately 460 mg EPA and 380 mg DHA), typically prescribed as 2-4 capsules daily

• Vazkepa (icosapent ethyl): A highly purified EPA formulation providing 998 mg EPA per capsule, usually prescribed as 2 capsules twice daily with meals

These prescription products undergo pharmaceutical manufacturing standards ensuring consistent omega-3 content, purity, and stability. They are formulated as ethyl esters to enhance absorption and reduce the gastrointestinal side effects sometimes associated with standard fish oil supplements.

When considering over-the-counter supplements, patients should examine the label carefully to determine actual EPA and DHA content rather than total fish oil content. A 1000 mg fish oil capsule may contain only 300 mg of combined EPA and DHA. For therapeutic triglyceride lowering, pharmaceutical-grade preparations are generally preferred due to their standardised potency and evidence base. Over-the-counter supplements are not licensed for treating hypertriglyceridaemia and should not substitute prescription products. Omega-3 supplements should be taken with meals to optimise absorption and minimise gastrointestinal discomfort. Patients taking warfarin should have their INR monitored when starting or changing the dose of omega-3 supplements.

Who Should Consider Fish Oil for High Triglycerides

Prescription omega-3 therapy is most appropriate for individuals with moderate to severe hypertriglyceridaemia, typically defined as fasting triglyceride levels above 2.3 mmol/L, particularly when levels exceed 5.6 mmol/L. At very high concentrations (above 10 mmol/L), triglycerides pose an acute risk of pancreatitis, and aggressive triglyceride-lowering therapy is warranted. In severe hypertriglyceridaemia, fibrates (such as fenofibrate) are usually considered first-line treatment to reduce pancreatitis risk, with high-dose omega-3 fatty acids potentially used as adjunctive therapy.

UK clinical guidance suggests urgent referral for specialist assessment when triglycerides are persistently above 20 mmol/L, or above 10 mmol/L despite treatment. Non-urgent referral may be appropriate for levels above 7.5 mmol/L with additional risk factors. Urgent same-day assessment is needed if pancreatitis is suspected (severe abdominal pain, nausea, vomiting).

Patients already receiving statin therapy for cardiovascular risk reduction who have residual hypertriglyceridaemia represent another group who may benefit from specific omega-3 supplementation. NICE Technology Appraisal 805 recommends icosapent ethyl (Vazkepa) with statins for reducing cardiovascular risk in adults with established cardiovascular disease who have raised triglycerides (1.5-5.6 mmol/L) and controlled LDL cholesterol. This indication relates specifically to Vazkepa rather than fish oil supplements generally.

Before initiating omega-3 therapy, clinicians should:

• Identify and address secondary causes of hypertriglyceridaemia (poorly controlled diabetes, excessive alcohol intake, obesity, hypothyroidism, certain medications)

• Ensure dietary modification has been attempted, including reduced refined carbohydrate and alcohol intake

• Assess for familial hypertriglyceridaemia or mixed dyslipidaemia requiring specialist lipid clinic referral

• Consider whether prescription omega-3 preparations are more appropriate than over-the-counter supplements

Patients with familial chylomicronaemia syndrome or severe genetic hypertriglyceridaemia typically require specialist management and may need multiple therapeutic approaches beyond omega-3 supplementation alone.

Potential Side Effects and Safety Considerations

Omega-3 fatty acids are generally well-tolerated, though several side effects and safety considerations warrant attention. The most common adverse effects are gastrointestinal, including nausea, diarrhoea, abdominal discomfort, and fishy aftertaste or eructation (burping). According to product information, these symptoms are common (affecting between 1 in 10 and 1 in 100 people) but are usually mild and can be minimised by taking capsules with meals or temporarily reducing the dose. Freezing capsules before consumption may also reduce fishy aftertaste.

Omega-3 fatty acids possess mild antiplatelet effects, theoretically increasing bleeding risk, though clinically significant bleeding complications are rare at therapeutic doses. Patients taking anticoagulants (warfarin, DOACs) or antiplatelet agents (aspirin, clopidogrel) should inform their healthcare provider before starting high-dose omega-3 therapy. Those on warfarin should have their INR monitored when starting or changing the dose of omega-3 supplements. Caution is appropriate in patients with bleeding disorders or those undergoing surgery.

Some studies have identified a small increase in LDL cholesterol with certain omega-3 formulations, particularly those containing DHA. This effect is generally considered clinically insignificant in the context of substantial triglyceride reduction, but lipid profiles should be monitored. Liver enzyme elevations may occur in some patients, and periodic monitoring may be appropriate, particularly in those with hepatic impairment. The Vazkepa (icosapent ethyl) product information notes an increased incidence of atrial fibrillation compared to placebo, though the absolute risk remains low. Patients should be counselled about recognising symptoms of atrial fibrillation (palpitations, breathlessness, dizziness).

Patients should contact their GP if they experience:

• Severe abdominal pain (potential pancreatitis, though rare)

• Unusual bleeding or bruising

• Irregular heartbeat or palpitations

• Allergic reactions (rash, swelling, breathing difficulty)

Omega-3 supplements derived from fish may pose concerns for individuals with fish or shellfish allergies, though severe allergic reactions are uncommon with purified preparations. Pregnant women should avoid cod liver oil supplements due to their vitamin A content, and should discuss any omega-3 supplementation with their healthcare provider. Patients are encouraged to report any suspected side effects to the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).

Frequently Asked Questions