If omega 3 is acting as blood thinner, why not stop taking coumadin and use omega 3 istead?

i know omega three is good for the body but i think the omega three only takes care of what it gives good fat and nourishes our bodys accordingly its good for our system but now coumadin is a blood thinner and thats what its used for my son was on coumadin for 6 months and he didn't need it anymore some people do still take it so i believe some can take and come off it i knew nothing i have heard isn't associated with omega 3 dr must think you need to be on coumadin or i'm sure he would have taken you off of it