The Setup: How a Billion-Dollar Industry Sells You Hope

The fish oil supplement market is built on a single, emotionally powerful premise: that you can protect your heart by swallowing a capsule. The science behind that premise has crumbled. The marketing has not.

• One person dies every 33 seconds in the United States from heart disease. In 2021, coronary heart disease alone killed 375,476 Americans, more than all forms of cancer and chronic lower respiratory disease combined that year.
• Heart disease fear has fueled a multibillion-dollar omega-3 supplement industry. Consumers are actively looking for ways to protect themselves, and supplement marketers have exploited that anxiety for decades.
• A JAMA Cardiology study examining more than 2,800 fish oil supplement labels found that heart health claims were the single most common type of claim made on these products, usually structured as “supports heart health” or equivalent phrasing.
• The same JAMA study concluded that these labels “increase the potential for consumer misinformation” because the claims are made despite a documented lack of clinical trial evidence supporting them.
• One in five U.S. adults over 60 takes fish oil supplements, a demographic that is simultaneously the most anxious about cardiovascular health and the most vulnerable to actual cardiac side effects.
• Registered dietitian Scott Keatley of Keatley Medical Nutrition Therapy explained the marketing capture bluntly: “Once a narrative becomes deeply embedded in popular culture, it can be difficult to change, even when new evidence emerges.”

The Products: What Costco Is Selling You

Costco’s Kirkland Signature brand carries two fish oil supplement products at issue in this lawsuit. Both carry the same front-label claim. Neither mentions the documented risks.

• Product 1: Kirkland Signature 1000 mg Fish Oil. Sold at Costco warehouse locations nationwide, including the Carlsbad, California location where plaintiff Donna Costan purchased it.
• Product 2: Kirkland Signature Wild Alaskan 1400 mg Fish Oil. A higher-dose variant sold under the same Kirkland Signature private label.
• Both products display “Helps Support a Healthy Heart” on the front label. Both prominently call out their Omega-3 content. The complaint refers to this front-label language as the “Heart Health Representation.”
• Neither product label mentions the risk of atrial fibrillation. Neither discloses that multiple large-scale clinical trials found no cardiovascular benefit. Neither notes that the NIH has formally stated omega-3 supplements do not reduce the risk of heart disease. These omissions are described in the complaint as the “Heart Health Omissions.”
• The FDA requires that structure/function claims on dietary supplements be “truthful and non-misleading” under 65 Fed. Reg. 1000. The complaint alleges that Costco’s label language violates this requirement and also violates California’s CLRA, FAL, and UCL statutes.

The Non-Financial Ledger: What No Settlement Check Can Repair

Donna Costan is a resident of Carlsbad, California. She is not a legal abstraction. She went to her local Costco and picked up a bottle of fish oil because she believed, reasonably and sincerely, that it would help protect her heart. She read the front label. It said “Helps Support a Healthy Heart.” She trusted it.

That trust is the product being sold here. Costco’s Kirkland Signature brand exists precisely because people trust it. The whole value proposition of the Kirkland label is that you are getting something vetted, something reliable, something that a warehouse giant has stood behind. When a person with genuine anxiety about their cardiovascular health hands money to Costco and receives a product labeled as supporting that health, the transaction carries a weight that the words “price premium” do not capture.

She did not know, because the label did not tell her, that the National Institutes of Health had formally concluded that omega-3 supplements do not reduce the risk of heart disease. She did not know that a government review of 98 separate studies found no evidence these supplements reduce the risk of heart attacks or cardiac death. She did not know that a major clinical trial had been stopped early because participants taking omega-3 supplements developed atrial fibrillation at a higher rate than those taking a placebo.

Atrial fibrillation is a serious, chronic, and potentially fatal heart condition. It causes the upper chambers of the heart to beat chaotically and out of sync. It raises the risk of stroke. It can lead to heart failure. Johns Hopkins Medicine describes its core problem plainly: it results from the heart “not pumping as well as it should.” This is the condition that multiple studies link to the very supplements Costco sold as heart-protective.

There is a particular cruelty in selling a heart health product to someone who is worried about their heart, when the product may be making their heart situation worse. The person who buys fish oil at 62 because they had a parent die of a heart attack, the person who is managing their cholesterol and trying to do everything right, the person on a fixed income who prioritizes supplements in their budget because they believe they are investing in their longevity: these are the people this marketing captures most completely.

One in five Americans over 60 takes fish oil supplements. That is not a small number of naive consumers. That is tens of millions of people who have been told the same story for years by an industry that R. Preston Mason of Harvard Medical School described as offering a “false promise.” The complaint makes clear that this is a deliberate competitive strategy: Costco labels its products with heart health claims “to gain a competitive edge” over fish oil supplements that do not use such claims. The deception is the business model.

The complaint also notes that Costco was warned. A formal notice letter was sent on January 5, 2024, identifying the CLRA violations and giving the company 30 days to fix the labeling. Costco did not respond by changing the labels. The lawsuit was filed November 18, 2024. Those products, with those labels, are still on warehouse shelves. More bottles are being purchased right now by people who do not know any of this.

No settlement will undo the months or years that people spent believing they were protecting their hearts while potentially doing the opposite. No restitution check will reach the people who developed atrial fibrillation during those years and never connected it to a supplement they took in good faith. The money part of this case is real and it matters. But the ledger of what was actually taken from these consumers runs deeper than any dollar amount.

Legal Receipts: What the Documents Actually Say

The following are verbatim quotes drawn directly from the complaint (Case 3:24-cv-02156-JO-AHG) and the scientific authorities it cites. These are the specific statements the lawsuit is built on.

“Consumers have been told so many times that dietary fish oil supplements promote heart health that it seems to be accepted as factual. But this conventional thinking is not supported by the science. After decades of promises that fish oil ‘may work,’ the lack of demonstrated benefit leads me to conclude that consumers are wasting their money on supplements in an effort to reduce cardiovascular risk.” R. Preston Mason, Cardiovascular Division, Brigham and Women’s Hospital and Harvard Medical School, Scientific American, August 22, 2019 (cited in complaint paragraph 39)

“There have now been a large number of well-conducted studies which have not shown a cardiac benefit to taking over-the-counter fish oil supplements. There is data these supplements may increase the risk of atrial fibrillation.” Timothy Jacobson, MD, Chief Cardiologist, Kaiser Permanente Northwest, quoted in health.com, August 29, 2023 (cited in complaint paragraph 50)

“A 2018 analysis of 10 major omega-3 supplementation studies (77,917 total participants, all at high risk of heart disease), each of which involved at least 500 participants and a treatment duration of at least a year, found no evidence that omega-3s could reduce the risk of fatal or nonfatal coronary heart disease.” NIH, National Center for Complementary and Integrative Health, U.S. Department of Health and Human Services (cited in complaint paragraph 48)

“With regard to prespecified tertiary end points, an increased rate of investigator-reported new-onset atrial fibrillation was observed in the omega-3 CA group.” STRENGTH Randomized Clinical Trial, JAMA, November 15, 2020 (cited in complaint paragraph 58)

“Patients who choose to take omega-3 fatty acids, especially in high doses, should be informed of the risk of [atrial fibrillation] and followed up for the possible development of this common and potentially hazardous arrhythmia.” Gregory Curfman, MD, Assistant Professor of Medicine, Harvard Medical School; former editor-in-chief, Harvard Health Publishing; JAMA, March 16, 2021 (cited in complaint paragraph 59)

“Results of this cross-sectional study suggest that fish oil supplement labels frequently include health claims in the form of structure/function claims that imply health benefits across a wide range of organ systems, increasing potential for consumer misinformation.” Assadourian et al., JAMA Cardiology, August 23, 2023 (cited in complaint paragraph 54)

The Timeline: From Science to Lawsuit

Societal Impact Mapping: Who Gets Hurt and How

Public Health

The false heart health narrative surrounding fish oil supplements carries concrete public health consequences when people replace effective interventions with a product that has no proven benefit and a documented risk.

• One person dies every 33 seconds in the United States from heart disease. When people with cardiovascular risk rely on a supplement that multiple clinical trials have shown provides no cardiovascular protection, they may delay or deprioritize interventions that actually work, such as medication, dietary changes, or physician-supervised care.
• One in five U.S. adults over 60 takes fish oil supplements, predominantly for heart health. This translates to tens of millions of people acting on a belief that leading cardiologists describe as a marketing myth with no clinical trial support at supplement-range doses.
• Multiple studies, including the STRENGTH Randomized Clinical Trial (which was halted early), found that omega-3 supplement users showed higher rates of new-onset atrial fibrillation compared to placebo groups. Atrial fibrillation is a chronic, progressive cardiac condition that increases stroke risk and can lead to heart failure. People consuming these supplements for heart protection may be acquiring a heart condition in the process.
• Harvard Medical School’s Gregory Curfman, MD, formally called for patients taking omega-3s to be monitored for atrial fibrillation development. No over-the-counter supplement label triggers any such monitoring. The gap between professional medical guidance and consumer reality is total.
• A 2024 prospective cohort study published in BMJ Medicine found that for people with a healthy cardiovascular profile, regular use of fish oil supplements was associated with an increased risk of atrial fibrillation, and that “findings do not support the use of fish oil or omega-3 fatty acid supplements for the primary prevention of incident atrial fibrillation” in generally healthy individuals. The people most likely to buy a heart health supplement at Costco are precisely the “generally healthy” individuals this study was warning about.

Economic Inequality

The financial harm from this scheme lands heaviest on the consumers who can least afford to waste money on products that do not work as advertised.

• Consumers pay a price premium for Kirkland Signature Fish Oil specifically because the heart health label claim signals quality and efficacy. The complaint states that Plaintiff and class members “would have paid significantly less for the Products, or would not have purchased them at all” if they had known the truth. They paid for a benefit that does not exist.
• Costco operates as a membership warehouse model with its own private-label brand. The Kirkland Signature name carries an implicit institutional endorsement. A consumer who buys Kirkland supplements is not buying from a random supplement vendor; they are buying from a corporation that they pay a membership fee to trust. That additional layer of implied institutional reliability makes the deception more effective and the betrayal more complete.
• The class is defined as all California residents who purchased either Kirkland fish oil product during the statute of limitations period. The aggregate amount in controversy exceeds $5,000,000. This is not a case involving a handful of wealthy plaintiffs; it involves thousands of ordinary consumers across the state, the vast majority of whom individually lost modest amounts that would never justify a solo lawsuit.
• The complaint explicitly notes that “many of the Class members may be unaware that claims exist against the Defendant,” meaning the economic injury to most victims of this scheme will go uncompensated unless the class action mechanism works as designed. This is the precise population that collective legal action exists to protect.
• The elderly population, which takes fish oil at the highest rate, is also the population most likely to be on fixed incomes. Diverting a portion of a limited monthly budget toward a supplement sold on a false health claim is a genuine economic injury to people who have limited ability to absorb it.

The “Cost of a Life” Metric

What Now? How to Fight Back

The lawsuit is live in federal court. Here is who is being held accountable, which regulators need to hear from you, and what you can do right now.

Who Is Accountable

• Costco Wholesale Corporation, Washington State corporation, principal place of business in Issaquah, Washington. The defendant in Case 3:24-cv-02156-JO-AHG. Responsible for the development, manufacturing, packaging, labeling, advertising, distribution, and sale of the Kirkland Signature Fish Oil products.
• Treehouse Law, LLP (Santa Monica, CA) filed the complaint on behalf of plaintiff Donna Costan and all similarly situated class members: Ruhandy Glezakos, Benjamin Heikali, Joshua Nassir, and Katherine Phillips. If you purchased Kirkland Fish Oil in California, you may be a class member.

Regulatory Watchlist

• U.S. Food and Drug Administration (FDA): Regulates dietary supplement labeling. The FDA requires structure/function claims to be “truthful and non-misleading” under 65 Fed. Reg. 1000. File a MedWatch report or a dietary supplement complaint at fda.gov/safety/medwatch if you believe a supplement label misled you.
• Federal Trade Commission (FTC): Regulates deceptive advertising. If a supplement advertises health benefits that lack adequate scientific support, that may constitute deceptive advertising under FTC rules. Report at reportfraud.ftc.gov.
• California Department of Consumer Affairs / California AG: The CLRA and UCL claims in this lawsuit are California state law claims. The California Attorney General enforces consumer protection statutes independently of private litigation. Contact consumeraffairs.ca.gov.
• NIH National Center for Complementary and Integrative Health: Already publicly maintains consumer guidance explicitly stating that omega-3 supplements do not reduce heart disease risk. Share the NIH fact sheet (nccih.nih.gov) with anyone you know taking fish oil for heart health.

Grassroots Resistance: What You Can Actually Do

• If you are a California resident who purchased Kirkland Signature 1000 mg Fish Oil or Kirkland Signature Wild Alaskan 1400 mg Fish Oil during the statute of limitations period, you may be a member of the class. Contact Treehouse Law LLP at the contact details listed in the complaint to find out how to participate.
• Talk to people in your family and community who take fish oil for heart health. Share the NIH fact sheet. Share this article. The harm from this labeling is being amplified every day by word of mouth repetition of a myth the supplement industry spent decades embedding in the culture. Reversing that requires the same mechanism.
• When you see “Helps Support a Healthy Heart” on any supplement label, photograph it, note the brand and store, and report it to both the FDA (MedWatch) and the FTC. The JAMA study found that more than 2,800 fish oil products carry these claims. Every single one of those products may be making the same misrepresentation Costco is now being sued for.
• Mutual aid networks in California: connect seniors in your community with the California Senior Legal Hotline (seniortop.org) or the Bet Tzedek Legal Services consumer protection unit. People on fixed incomes who have been purchasing these supplements for years often have meaningful but unclaimed legal rights.
• Push your local Costco store to remove the heart health claim from these labels proactively. Costco has a customer feedback mechanism at costco.com. Pressure from members, the same members who pay annual fees for the privilege of shopping there, is a direct lever on corporate behavior before a court orders it.