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.

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.

Fish oil supplements with higher concentrations of EPA and DHA tend to cost more, but paying more does not guarantee the product is less oxidized or more stable once you account for the actual EPA and DHA content.

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.

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.

A study found that most fish oil supplements sold in New Zealand contained significantly less of the key omega-3 fatty acids (EPA and DHA) than stated on their labels, with only a small number meeting their advertised content.