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.

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.

Laboratory testing of two fish oil supplements revealed that one contained significantly less EPA than stated on the label, while another contained more DHA than claimed.

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.