Omega XL is generally well tolerated, but it can cause digestive side effects, and certain people need to avoid it entirely. The supplement contains PCSO-524, a patented oil extract from New Zealand green-lipped mussels, which delivers omega-3 fatty acids in a different form than standard fish oil. Most side effects are mild and centered in the gut, though a few deserve closer attention.
Common Digestive Side Effects
The most frequently reported side effects of omega-3 supplements like Omega XL are gastrointestinal. These include nausea, diarrhea, bloating, a feeling of fullness or pressure in the stomach, and vomiting. Less common but still possible are stomach pain, belching, and excess gas.
These symptoms often show up in the first week or two of use and may ease as your body adjusts. Taking the capsules with food can help reduce stomach upset. If digestive symptoms persist beyond the first few weeks, that’s a sign your body may not be handling the supplement well.
Arthritis UK notes that green-lipped mussel products are “relatively well tolerated,” with nausea and flatulence being the main complaints. Constipation is also possible, though less common than loose stools.
Shellfish Allergy Risks
Because Omega XL is derived from green-lipped mussels, a type of shellfish, anyone with a shellfish allergy should avoid it. The proteins that trigger allergic reactions may still be present in the final product despite processing. Reactions could range from mild hives to something more serious.
If you’re allergic to shellfish but tolerate finned fish without problems, the risk from a standard fish oil supplement would be very low, according to the American Academy of Allergy, Asthma & Immunology. But Omega XL is not standard fish oil. It’s a mussel extract, which puts it squarely in the shellfish category. That distinction matters.
Interactions With Blood Thinners
Omega-3 fatty acids can extend the time it takes for blood to clot. If you take anticoagulants like warfarin, or even over-the-counter anti-inflammatory drugs like aspirin or ibuprofen, adding Omega XL could increase your risk of bleeding or bruising. The National Institutes of Health specifically flags this interaction, recommending that anyone on blood-clotting medications talk with their provider before starting an omega-3 supplement.
Arthritis UK echoes this caution for green-lipped mussel products in particular, noting that interactions with anticoagulants haven’t been well studied. The lack of data is itself a reason to be careful. You may not notice a problem until you get a cut that won’t stop bleeding or develop unusual bruising.
What Clinical Trials Show About Safety
A clinical trial published in Respiratory Medicine tested PCSO-524 (the extract in Omega XL) in asthma patients taking eight capsules daily for three weeks. Compliance was high, with a median of 99% of capsules taken as directed, and no significant safety concerns were reported during the study period. However, the study excluded people with bleeding disorders, delayed clotting time, high blood pressure, and diabetes, so the results don’t speak to how the supplement behaves in those populations.
Each Omega XL capsule contains about 50 mg of omega-3 fatty acids plus 100 mg of olive oil. That’s a much smaller omega-3 dose per capsule than most standard fish oil supplements, which typically deliver 300 to 500 mg per capsule. The manufacturer recommends taking the capsules with food, but no universally agreed-upon safe dose has been established for green-lipped mussel extract in joint or inflammatory conditions.
Who Should Be Cautious
Several groups should think twice before starting Omega XL:
- People with shellfish allergies. The mussel-based origin makes this a direct concern, not a theoretical one.
- People on blood thinners or anti-inflammatory medications. The omega-3 content may amplify bleeding risk.
- Pregnant or nursing women. The NIH recommends consulting a provider before using omega-3 supplements during pregnancy.
- People with sensitive stomachs. If you already deal with nausea, bloating, or irritable bowel symptoms, the digestive side effects may be more noticeable.
Because Omega XL is sold as a dietary supplement rather than a prescription drug, it isn’t subject to the same rigorous testing that medications go through before reaching the market. That doesn’t mean it’s unsafe, but it does mean the safety data is thinner than what you’d find for a prescription omega-3 product. If you experience persistent stomach problems, unusual bruising, or any signs of an allergic reaction after starting Omega XL, those are worth taking seriously.