What is the downside to taking krill oil?

Krill oil thins the blood, so people with bleeding disorders should not take it, as stated by WebMD. Krill oil is not an established treatment for any condition, and the excess harvesting of krill takes food away from populations of whales, penguins and some other birds.

Because of its blood thinning properties, people should not take krill oil for two weeks before surgeries, according to WebMD. Women who are nursing or pregnant should consult a physician before taking krill oil, as it is not rated for safety for children. People taking blood thinners and antiplatelet medications should also stay away from krill oil.