They may cause or contribute to birth defects and cancers, as well as causing outright symptoms of poisoning.

This document will verify that there was no detectable level of contaminants. A capsule usually contains 500-1000mg of oils. A dosage of fish oil is sometimes recommended for pregnant women,.

It is primarily because of mercury and PCBs that people, particularly women and children, are advised to limit their consumption of certain species of fish. Some, such as swordfish, should be avoided entirely. The contaminants of most concern are mercury and PCBs.

The content of the capsules on the market varies greatly. What is the Best Dosage of Fish Oil. Some brands contain distilled esters, which have a higher concentration of omega-3s and usually a lower concentration of contaminants. Other brands contain the natural triglycerides, which may, according to some evidence, provide more health benefits, but they must be tested thoroughly for contaminants and the omega-3 content will naturally be lower. If a company uses natural triglycerides, the consumer should check for a "Certificate of Analysis" or COA from an independent laboratory.

Most sources suggest that the correct daily dosage of fish oil is 2-3 capsules, but that is a very non-specific suggestion.