Can I Take Fish Oil and Krill Oil Together?

Taking fish oil and krill oil together is safe for most people, and there is no known interaction between the two supplements. Both deliver the same omega-3 fatty acids, EPA and DHA, so the real question is not whether combining them is dangerous but whether it is worth the money. Since the two oils carry their omega-3s in different molecular forms, some people stack them hoping for better absorption or broader benefits, but the evidence for a meaningful advantage over simply taking a sufficient dose of either one alone is thin.

What Actually Differs Between the Two Oils

Fish oil and krill oil both supply EPA and DHA, the two long-chain omega-3 fats linked to cardiovascular, brain, and joint health. The difference is packaging. In fish oil, most of the EPA and DHA are bound to triglycerides. In krill oil, roughly 30 to 65 percent of the fatty acids are bound to phospholipids, mainly phosphatidylcholine.¹ Krill oil also contains astaxanthin, a carotenoid pigment with antioxidant properties that gives it its reddish color.²

This structural difference is the basis for most marketing claims about krill oil’s superiority. Phospholipids are a major component of cell membranes, so the theory is that omega-3s delivered in phospholipid form integrate into cells more efficiently. Fish oil’s triglyceride-bound omega-3s, by contrast, need to be broken down by digestive enzymes before reassembly. Whether that molecular distinction translates to a meaningful real-world difference in your body is where things get interesting.

Does One Get Absorbed Better Than the Other?

Several head-to-head trials have compared how well EPA and DHA from krill oil versus fish oil end up in your blood. The results are surprisingly close. A four-week randomized trial found no significant differences in total plasma EPA and DHA between people taking fish oil (in either triglyceride or ethyl ester form) and those taking krill oil, with bioavailability differing by less than about a quarter between the groups. Red blood cell omega-3 levels, a more stable marker, were also comparable across formulations.³

An earlier crossover study did observe numerically higher EPA and DHA incorporation into plasma phospholipids from krill oil compared with fish oil, but the differences were not statistically significant due to wide variation between individuals.⁴ And a more recent crossover study comparing krill oil against a phospholipid-enhanced fish oil found similar 24-hour EPA and DHA absorption between the two, though the enhanced fish oil reached its peak blood concentration faster.⁵

The upshot: krill oil may have a slight edge in absorption per milligram of EPA and DHA, but the difference is small enough that it has not consistently reached statistical significance across trials. If you are combining both oils, you are not getting some synergistic absorption boost. You are just getting more total omega-3s from two bottles instead of one.

Do the Health Effects Differ in Practice?

When it comes to hard outcomes like blood lipid changes, the two oils perform similarly gram-for-gram of EPA and DHA. A network meta-analysis comparing krill oil and fish oil across multiple trials found that both lowered triglycerides, and the difference between them was not significant. One gram of omega-3 fatty acids from fish oil lowered median triglycerides by about 9 mg/dL, while one gram from krill oil lowered them by about 10 mg/dL. The authors concluded that the triglyceride-lowering effect depends on the dose of omega-3s consumed, not which oil delivers them.⁶

A separate trial in healthy volunteers reinforced this, finding no significant differences in serum lipids, oxidative stress markers, or inflammation between people taking krill oil and those taking fish oil, even though the krill oil group received only about 63 percent as much EPA and DHA as the fish oil group.⁷ That hints at slightly better efficiency per milligram for krill oil, but it does not mean you need both.

Where there may be a subtle difference is inflammation. One clinical trial found that both krill oil and esterified omega-3 fatty acids significantly reduced high-sensitivity C-reactive protein (a marker of systemic inflammation), but krill oil reduced it more effectively.⁸ Whether that advantage comes from the phospholipid form, the astaxanthin, or some combination is still unclear. An animal study found that EPA and DHA levels in the brain were slightly higher with krill oil after long-term use, though not significantly so.⁹

A trial in patients with major depressive disorder found that krill oil recipients had lower triglycerides and HbA1c after the intervention period.¹⁰ But single trials in specific patient populations should not be over-read. The overall picture is that both oils produce broadly similar benefits for most cardiovascular and metabolic markers.

How Much Is Too Much If You Combine Them?

The main safety consideration when stacking two omega-3 supplements is total dose. The European Food Safety Authority reviewed the evidence and concluded that supplemental intakes of EPA and DHA combined at doses up to 5 grams per day do not raise safety concerns for adults.¹¹ Most standard-dose fish oil capsules supply about 300 to 500 mg of combined EPA and DHA, and most krill oil capsules supply about 100 to 250 mg. Even if you take both at their recommended serving sizes, you are unlikely to approach 5 grams per day unless you are also taking a prescription-strength omega-3.

That said, you should still read labels and do the arithmetic. A common scenario is someone taking two fish oil softgels (about 600 mg of EPA and DHA) plus two krill oil capsules (about 300 mg of EPA and DHA) daily, totaling around 900 mg. That is well within safe limits and roughly in line with what most health organizations suggest for general cardiovascular maintenance. The problems start when people layer multiple high-dose products, or combine over-the-counter supplements with prescription omega-3 concentrates, without realizing how the total adds up.

Bleeding Risk and Blood Thinners

The old concern about omega-3s and bleeding deserves a careful look, especially for anyone taking both oils simultaneously. A meta-analysis of randomized trials found that high-dose purified EPA was associated with a 50 percent increase in relative bleeding risk, but the absolute increase was only about 0.6 percent compared with placebo. Bleeding risk correlated with the dose of EPA specifically.¹² That context matters: the elevated risk was seen at pharmaceutical doses (roughly 4 grams per day of EPA), not at typical supplement levels.

In healthy people, the picture is reassuring. A well-powered study of healthy volunteers found no effects of high-dose omega-3 fatty acids on coagulation or platelet function after 10 days of intake.¹³ A meta-analysis of platelet aggregation studies did find that omega-3 supplementation reduced platelet aggregation in people with existing health problems, but not in healthy individuals.¹⁴

What about people on warfarin or other blood thinners? A retrospective study of patients with atrial fibrillation or deep vein thrombosis found that fish and krill oils did not significantly alter warfarin’s time in therapeutic range or bleeding incidence.¹⁵ Still, if you are on anticoagulant therapy, doubling up on omega-3 supplements without telling your doctor is not a great idea. The risk is small, but the consequences of unexpected bleeding are not.

For anyone facing surgery, the news is also encouraging. A study of fish oil supplementation around the time of cardiac surgery found no increased risk of bleeding compared with placebo. In fact, total units of blood transfused were actually lower in the fish oil group.

Shellfish Allergies and Krill Oil

This is where combining the two oils introduces a concern that does not apply to fish oil alone. Krill are crustaceans, which puts them in the same biological family as shrimp, crab, and lobster. The major allergen in shellfish is tropomyosin, a muscle protein that shares structural similarities across crustacean and arthropod species. If you have a confirmed IgE-mediated shellfish allergy, krill oil capsules could trigger a reaction.

In practice, most krill oil undergoes extensive processing that removes much of the protein content, and allergic reactions to purified krill oil supplements are rarely reported. But “rarely reported” is not the same as “impossible,” and the risk tolerance for anaphylaxis is understandably low. If you have a shellfish allergy, sticking with fish oil alone is the safer choice. Fish allergies and shellfish allergies are distinct; having one does not automatically mean you have the other, since the allergenic proteins differ. Someone allergic to fish but not shellfish could theoretically tolerate krill oil, and vice versa, but cross-contamination during manufacturing is always a possibility.

Oxidation and Shelf Life

One genuine advantage krill oil holds over fish oil has nothing to do with your body. It has to do with the bottle sitting on your shelf. A study comparing the oxidative stability of the two oils found that krill oil degraded more slowly than fish oil, with lower levels of volatile lipid oxidation products and slower oxygen consumption.¹⁶ The astaxanthin in krill oil likely contributes to this stability.

This matters because oxidized fish oil not only tastes terrible (those fishy burps) but may also lose some of its beneficial properties. If you are combining both supplements, the krill oil capsules will probably outlast the fish oil capsules on the shelf. Regardless, storing both in a cool, dark place and checking for rancid odors before taking them is good practice. If your fish oil smells strongly fishy when you open the bottle, it has likely oxidized and should be replaced.

Label Accuracy Is a Bigger Problem Than You Think

Before worrying about whether to combine two omega-3 products, it is worth knowing that the products themselves often do not contain what they claim. A U.S. study found that about half of retail omega-3 supplements contained less EPA and DHA than declared on the label.¹⁷ Another U.S. study testing 47 brands found that over 70 percent did not contain the stated label amount of EPA or DHA, with some delivering as little as two-thirds of the claimed dose.¹⁸ A New Zealand analysis found even worse compliance, with supplements containing on average only 68 percent of the claimed EPA and DHA content, and some containing roughly a third.¹⁹

This applies to both fish oil and krill oil products. The practical implication is that combining two underdosed supplements might bring you closer to the amount a single properly dosed product should deliver. If you want to know what you are actually getting, look for brands that provide third-party testing certificates (often called a Certificate of Analysis or COA). The International Fish Oil Standards (IFOS) program and organizations like NSF International or USP test supplements for potency, purity, and oxidation levels.

When Combining Actually Makes Sense

For most people, there is no compelling reason to take both fish oil and krill oil. If your goal is a target omega-3 intake of, say, 1,000 mg of EPA and DHA daily, you can get there more cheaply with fish oil alone, since krill oil capsules tend to cost more per milligram of omega-3. If you prefer krill oil because you tolerate it better (fewer burps, smaller capsules), there is no reason to add fish oil on top unless your krill oil dose falls short of your target.

There are a few scenarios where stacking might have a rationale, if not rock-solid evidence. Some people take a standard fish oil for the bulk of their omega-3s and add a krill oil capsule specifically for the phospholipids and astaxanthin, treating it more like an antioxidant booster than a second omega-3 source. Others find that they tolerate one oil better at certain times of day and split their intake. Neither approach is harmful as long as total EPA and DHA stays under 5 grams per day. Whether the phospholipid form provides a clinically meaningful benefit on top of triglyceride-bound omega-3s has not been tested in a well-designed combination trial. It is a reasonable hypothesis that has yet to be proven.

Environmental Considerations

Krill are a keystone species in Antarctic ecosystems, forming the base of the food chain for whales, penguins, seals, and countless fish species. The environmental footprint of krill harvesting is a genuine concern. A life cycle analysis found that roughly 190 liters of fuel are burned per tonne of raw krill landed, which is markedly higher than fuel inputs for other reduction fisheries.²⁰ However, the same study noted that the biotic resource use (the impact on the living ecosystem) associated with krill extraction is relatively low compared with other reduction fisheries, largely because the Antarctic krill fishery is managed under strict international quotas through the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

If you are already taking fish oil and considering adding krill oil, the environmental math is straightforward: you are now drawing from two marine sources instead of one. For people who factor ecological impact into supplement choices, getting all your omega-3s from a single sustainably certified source, whether that is fish oil or krill oil, uses fewer total marine resources than splitting between both. Algal omega-3 supplements, which are produced from farmed microalgae rather than harvested marine animals, sidestep the issue entirely and are the only option that removes wild fisheries from the equation altogether.

Gastrointestinal Side Effects

The most common complaints with omega-3 supplements are fishy aftertaste, burping, nausea, and loose stools. These tend to be milder with krill oil than with fish oil, likely because of the smaller capsule size (which means a smaller volume of oil per dose) and the phospholipid form, which emulsifies more readily in the stomach. Adding fish oil to a krill oil routine, or vice versa, could increase GI symptoms simply because you are swallowing more oil total. Splitting doses across meals rather than taking everything at once tends to help, as does choosing enteric-coated capsules that dissolve in the small intestine instead of the stomach.

Some people find that krill oil is gentler enough to serve as their daily baseline, with fish oil reserved for days when they eat no fatty fish. This alternating approach keeps the total daily oil volume lower while still maintaining consistent omega-3 intake across the week. There is no evidence that the two oils interact negatively in the gut, so timing and personal tolerance are the only real constraints.