There are very few for the vast majority of the population, but the most common is a fishy burp, which can be eliminated with a proper formulation. Other potential precautions and contraindications for sub-populations are listed below:
Precautions
Fish oil supplements should be used by children, pregnant women and nursing mothers only if
recommended and monitored by a physician. Because of the possible anti-thrombotic effect of fish oil supplements, hemophiliacs and those taking warfarin (Coumadin) should exercise caution in their use. Fish oil supplements should be stopped before any surgical procedure. Conflicting results have been reported regarding the effects of fish oil supplements on glycemic control in those with glucose intolerance including Type II diabetics. Some early studies indicated that fish oil supplements might have detrimental effects in those groups. Recently, better-designed studies have not reported these adverse effects; in fact, studies are now suggesting benefits for diabetics. There is no evidence that fish oil supplements have detrimental effects on glucose tolerance, insulin secretion or insulin resistance in non-diabetic subjects. Diabetics should discuss the use of these supplements with their physicians and note if the supplements affect their glycemic control. Diabetics who take fish oil supplements should be monitored by their physicians.
Contraindications
• Anyone taking greater than three grams per day should do so only under the care of their physician due to risk of excessive bleeding at higher doses
• Should not be used if user is on anticoagulants or has uncontrolled hypertension
• May raise blood sugar and LDL in people with diabetes
Adverse Reactions
Fish oil supplementation is usually well-tolerated at three to four grams per day. Those side effects that have been reported include mild gastrointestinal upsets such as nausea and diarrhea, halitosis, eructation (belching) and “fishy” smelling breath, skin and even urine. Taking greater than three grams per day of n-3 fatty acids can cause excessive bleeding.