EyePromise Omega-3s are tested and safe. Commonly reported side effects of Omega-3 supplements are usually mild. These could include unpleasant taste, bad breath, heartburn, nausea, gastrointestinal discomfort, diarrhea, headache, and odoriferous sweat. In addition, Omega-3 dietary supplements, such as fish oil, have the potential to interact with medications such as Warfarin and other blood-thinning medications. People taking these and other medications on a regular basis should discuss possible interactions with their healthcare providers.