Omega 3 Fatty Acid Supplements and Autism Ranking: Insufficient/Mixed evidence

Risks and Safety


The quality of omega-3 supplements can vary enormously depending on the specific supplement, the manufacturer, the ingredients and the manufacturing process.  

Omega-3 supplements are generally safe, however we recommended that you discuss the safe trial of any nutritional supplements with your doctor before using them. We also suggest that you do not exceed the RIs (Reference Intakes) recommended by the Food Standards Agency in UK or the RDAs (Recommended Dietary Allowances) recommend by the Office of Dietary Supplements in the USA. 

Particular care is recommended to:
1. Avoid toxins such as mercury, hormones, dioxins, and PCBs, which are present in many fish oils. Supplements are available that have been purified by molecular distillation and which are described as pharmaceutical grade.
2. Avoid toxic doses of vitamin A, which is often included in fish oil supplements. Care should be taken to keep intake within the safe dose as recommended by the UK Department of Health, taking into account vitamin A levels in any additional supplements taken.
3. Avoid supplements containing any ingredients which you or your child or client are allergic or hypersensitive to.
4. Be wary of doses above 1000mg (1 gram) of omega-3 per day.
5. Be aware that fish oils supplements can affect blood sugar control in diabetes.
6. Be aware that high levels of fish oil supplementation can cause blood thinning, which could cause problems in people who bruise easily, self-harm, have a bleeding disorder, or take blood-thinning medications.
Side effects of taking fish oils can include repeating taste, heartburn, diarrhoea, and headaches.


There are very few contraindications (something which makes a particular treatment or procedure potentially inadvisable) for omega-3 fatty acid supplements.

However the National Institutes for Health (2017) noted that

“Omega-3 dietary supplements may interact with the medications you take. For example, high doses of omega-3s may cause bleeding problems when taken with warfarin … or other anticoagulant medicines.”


Dioxins (toxic chemical by-products of industrial processes); PCBs (polychlorinated biphenyls, synthetic organic chemicals that can cause a number of different harmful effects.)

14 Dec 2018
Last Review
01 Dec 2018
Next Review
01 Dec 2021