NOW DHA-500 has twice the DHA (500 mg per softgel) as in our regular strength product (250 mg per softgel). This natural fish oil concentrate is manufactured under strict quality control standards. It is tested to be free of potentially harmful levels of contaminants such as PCBs, dioxins, mercury and other heavy metals. Those who experience nausea or reflux from other fish oils should find this enteric coated, odor-controlled softgel easier to tolerate. Fish oil is product of India.