A test of 14 fish oil supplements in Bahrain found that only one had more EPA and DHA than stated on the label; most contained less than advertised, suggesting under-delivery is the primary quality issue.

Testing of 15 fish oil supplements sold in the U.S. found that some contained EPA or DHA levels that were more than 20% higher or lower than what was stated on the label, suggesting that label claims for these nutrients are often inaccurate.

Testing of fish oil supplements sold in Bahrain found that nearly half had less of the key omega-3 fats (EPA and DHA) than advertised, and some had more EPA but less DHA than labeled, indicating variability in product quality.

Fish oil supplements on the market contain different amounts of omega-3 fatty acids, with some having as little as 31.6% and others as much as 83.4% of their oil content, and the balance between omega-6 and omega-3 fats also varies significantly between products.

Fish oil supplements sold over the counter have more oxidized fats than prescription omega-3 products that meet international quality standards.

Many fish oil supplements sold commercially do not contain the amount of EPA and DHA claimed on their labels, show signs of degraded fats beyond safe limits, and may contain harmful contaminants like heavy metals.