I have been told that fish oil is a no-no for people on warfarin.
I know a few people here who are on warfarin and take fish oil.
The problem with warfarin advice is clinicians and even doctors have got negative knowledge (not just zero, things they "know" to be true are wrong).
Journals
like this try to fix the issue, but (even professional) people learn things via all sorts of channels including word of mouth or even a misplaced wrong opinion. From that link:
The mechanism for the anticoagulant activity of fish oil relates to changes in the ratio of phospholipids in platelet membranes, as fish oil decreases the synthesis of thromboxane A2 from arachidonic acid in platelets.9 Consumption of fish-rich diets or fish oil supplements may reduce platelet aggregation.9 Therefore, combined use of fish oil with anticoagulant or antiplatelet agents may, theoretically, increase the risk of bleeding.
In commonly used doses (<3 g daily), fish oil does not seem to increase the risk of bleeding, as previously suggested.4,9–11 However, the safety of higher doses (>3 g/day) is less clear.9 Although not confirmed in trials, bruising and minor bleeding are frequently reported by people taking fish oils, so it is wise to monitor for these potential adverse effects and reduce the dose if they occur.
Basically the world is slowly turning towards seeing that patient self testing is the ideal way (resisted by the clinics losing millions of people globally) to ensure that people know themselves.
So much of the advice people base their choices on is wrong - how can anyone be expected to make proper informed choies when the data they use to make the choice is wrong?
Test and Know Thyself
Best Wishes