While there are no published studies, as of February 2015, to make a definitive comparison of the blood thinning properties of krill and fish oils, supplementing medication with either oil is not advised for individuals taking blood thinners and those who have clotting problems. Fish oil has been observed to lessen blood coagulation and can potentiate the effects of blood thinners such as warfarin, thereby increasing the risk of bleeding. Since krill oil is similar to fish oil, it may pose the same health risks as fish oil.
A 2005 study suggested that the beneficial effects of krill oil supplementation may be better than those of fish oil supplementation. In a study conducted on 113 people measuring the effects of krill oil on hyperlidimia (high cholesterol levels), test subjects who took krill oil over the course three months showed an improved cholesterol profile that is better than the subjects who were given a course of fish oil and the placebo group.
The same study, which was published in the Alternative Medicine Review, showed that the test subjects who took krill oil also exhibited improved blood sugar levels. Another similar study, however, was not able to replicate the same effects with test subjects who had only slightly elevated blood cholesterol levels.
Other advantages of krill oil over fish oil include its higher rate of absorption because of its phospholipid-derived fatty-acids and higher and more potent antioxidant properties. These, however, are not enough to categorically determine whether or not krill oil has better blood thinning properties than fish oil.