Doses for depression range from less than 1 g/day to 10 g/day, but most studies use doses between 1 and 2 g/day. In my practice, I recommend 1 to 2 g/day of an EPA+DHA combination, with at least 60% EPA, for major depression. I am more cautious in patients with bipolar depression, because the omega-3s may bring on mania, as can most antidepressants. In these individuals, I recommend using omega-3 cautiously, and preferably in combination with a prescription mood stabilizer.
The US National Institutes of Health lists three conditions for which fish oil and other omega-3 sources are most highly recommended: hypertriglyceridemia (high triglyceride level), preventing secondary cardiovascular disease, and hypertension (high blood pressure). It then lists 27 other conditions for which there is less evidence. It also lists possible safety concerns: "Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke."[12]

Fish oil is effective in reducing inflammation in the blood and tissues. Regular consumption of fish oil supplements, tablets, pills, and capsules is helpful to those who suffer from chronic inflammatory diseases. Fish oil is effective in treating gastrointestinal disorders, Celiac disease, short bowel syndrome and inflammatory bowel disease (IBD) including Crohn’s Disease and ulcerative colitis, which are both typical disorders of the intestine. Patients suffering from Crohn’s disease often find it difficult to absorb vitamins, fats, and essential supplements. Fish oil supplements are an effective diet for such patients.
The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), found in plant oils, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both commonly found in marine oils.[2] Marine algae and phytoplankton are primary sources of omega−3 fatty acids. Common sources of plant oils containing ALA include walnut, edible seeds, clary sage seed oil, algal oil, flaxseed oil, Sacha Inchi oil, Echium oil, and hemp oil, while sources of animal omega−3 fatty acids EPA and DHA include fish, fish oils, eggs from chickens fed EPA and DHA, squid oils, and krill oil. Dietary supplementation with omega−3 fatty acids does not appear to affect the risk of death, cancer or heart disease.[4][5] Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes or any vascular disease outcomes.[6][7]

Respected health care organizations proposed intake recommendations for oily fish of two servings per week for healthy adults, which equates to approximately a daily total of 500 milligrams (mg) EPA and DHA.‡ The recommendation encourages adults already with or at-risk of developing cardiovascular disease to talk to their primary healthcare professional about supplementing with amounts greater than 500 mg of EPA and DHA per day. Supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease.
Additional side effects of fish oil supplements which have been reported include headache, short-term memory loss, depression, somatic disorders, and increased risk of colon cancer, nasopharyngitis, worsening of asthma symptoms, hemolytic anemia, decreased physical activity, increased appetite, a general uncomfortable feeling or increased blood pressure. The percentage of users that develop these side effects is not known. If these side effects become severe it is recommended that you stop using fish oil supplements.
One day I was cooking pasta when the kitchen started to fill with the odor of fish. I happen to hate fish, so this was not a pleasant experience. It was also a mystery, since I never cook fish. A little detective work discovered that the offensive odor was coming from the pasta. Apparently I didn’t notice the “Now with Omega 3” label on the box when I purchased it. My daughter and I still refer to this as the “fish pasta incident”.
Full citation: Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, Deane KHO, AlAbdulghafoor FK, Summerbell CD, Worthington HV, Song F, Hooper L. Omega 3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2018, Issue 7. Art. No.: CD003177. DOI: 10.1002/14651858.CD003177.pub3.
Good points, Miroslav. Focusing on your 4th point, with so many different formulations on the market that contain various preservatives, only looking at the blood levels of omega-3’s as the flag for increased risk for prostate cancer tends to ignore the fact that certain populations in coastal regions maintain a diet high in omega fish oils and don’t have a marked increase level of prostate cancer, pointing to the fact that another agent may be to blame here.
In short, there is no single optimal EPA:DHA ratio. If we are really healthy, with an optimal omega-6 to omega-3 ratio (from a diet rich in omega-3 fatty acids and low in grains and vegetable oils) and have an active, stress-free lifestyle, relying on standard fish oil in the natural 1.5:1 EPA:DHA ratio or simply consuming oily fish is completely adequate.

This under-the-radar grain is a nutritional powerhouse — and one of the most potent sources of the omega-3 alpha-Linolenic acid (ALA). Sprinkle flaxseeds over your morning oatmeal for a pleasant nutty flavor, or blend them into fruit smoothies to satisfy a picky palate. Need more ideas? Check out The Flaxseed Recipe Book, an easy-to-follow guide for adding flaxseeds to your favorite soups, salads, and main courses.

DHA is vital for early brain development and maintenance, while EPA seems to be closely related to behavior and mood. Together, both molecules provide critical neuroprotective benefits.11 These neuroprotective effects are important for the prevention of age-related brain shrinkage (cortical atrophy). Aging adults with brain shrinkage often experience memory loss, cognitive decline, and an increase in depression.12-14
Luo, J Rizkalla SW Vidal H Oppert JM Colas C Boussairi A Guerre-Millo M Chapuis AS Chevalier A Durand G Slama G. Moderate intake of n-3 fatty acids for 2 months has no detrimental effect on glucose metabolism and could ameliorate the lipid profile in type 2 diabetic men. Results of a controlled study. Diabetes Care. 1998;21(5):717-724. View abstract.
In many cases, people are recommended to consume fish oil because it is an easy way to get additional omega-3 fatty acids into their diet. Omega-3 fats can be used to reduce swelling or to prevent blood clots which could cause major cardiovascular damage. There are many other conditions which can be decreased or improved with the use of fish oil. In most cases fish oil is used to help reduce high triglycerides which can cause serious conditions like diabetes or heart disease.
Fearon, K. C., Von Meyenfeldt, M. F., Moses, A. G., Van Geenen, R., Roy, A., Gouma, D. J., Giacosa, A., Van Gossum, A., Bauer, J., Barber, M. D., Aaronson, N. K., Voss, A. C., and Tisdale, M. J. Effect of a protein and energy dense n-3 fatty acid enriched oral supplement on loss of weight and lean tissue in cancer cachexia: a randomised double blind trial. Gut 2003;52(10):1479-1486. View abstract.
There is, however, significant difficulty in interpreting the literature due to participant recall and systematic differences in diets.[53] There is also controversy as to the efficacy of omega−3, with many meta-analysis papers finding heterogeneity among results which can be explained mostly by publication bias.[54][55] A significant correlation between shorter treatment trials was associated with increased omega−3 efficacy for treating depressed symptoms further implicating bias in publication.[55]
Rogers, P. J., Appleton, K. M., Kessler, D., Peters, T. J., Gunnell, D., Hayward, R. C., Heatherley, S. V., Christian, L. M., McNaughton, S. A., and Ness, A. R. No effect of n-3 long-chain polyunsaturated fatty acid (EPA and DHA) supplementation on depressed mood and cognitive function: a randomised controlled trial. Br J Nutr 2008;99(2):421-431. View abstract.
The omega-3 PUFA EPA and DHA are important throughout life and are a dietary necessity found predominantly in fish and fish-oil supplements. The omega-3 fatty acids EPA and DHA are essential for proper fetal development, and supplementation during pregnancy has also been linked to decreased immune responses in infants including decreased incidence of allergies in infants. Omega-3 fatty acid consumption has been associated with improved cardiovascular function in terms of antiinflammatory properties, PAD, reduced major coronary events, and improved antiplatelet effects in the face of aspirin resistance or clopidogrel hyporesponsiveness. Patients with AD have been shown to be deficient in DHA, and supplementing them with EPA+DHA not only reverses this deficiency, but may also improve cognitive functioning in patients with very mild AD. With increasing rates of pediatric allergies, cardiovascular disease, and AD in the United States, EPA and DHA may be a safe and inexpensive link to a healthier life. Further research should be conducted in humans to assess a variety of clinical outcomes including quality of life and mental status. In addition, because potent lipid mediator metabolites of EPA and DHA are of great interest currently, their influence on these important outcomes should be assessed because current evidence suggests that their antiinflammatory and tissue-protective effects are nearly 1000 times greater than those of EPA and DHA (7).
The reason why fish oil could increase a man’s risk of prostate cancer is IMBALANCE. Like I said earlier, omega-6 fatty acids aren’t bad for you. In fact, if your diet contains too many omega-3 fatty acids, your immune system wouldn’t work very well because omega-3 and omega-6 fatty acids are meant to work in a system of checks and balances. Omega-3 fatty acids suppress inflammation, and omega-6 fatty acids promote inflammation, which actually supports your body’s natural system of defense like activating your white blood cells.
The American Heart Association (AHA) has made recommendations for EPA and DHA due to their cardiovascular benefits: individuals with no history of coronary heart disease or myocardial infarction should consume oily fish two times per week; and "Treatment is reasonable" for those having been diagnosed with coronary heart disease. For the latter the AHA does not recommend a specific amount of EPA + DHA, although it notes that most trials were at or close to 1000 mg/day. The benefit appears to be on the order of a 9% decrease in relative risk.[106] The European Food Safety Authority (EFSA) approved a claim "EPA and DHA contributes to the normal function of the heart" for products that contain at least 250 mg EPA + DHA. The report did not address the issue of people with pre-existing heart disease. The World Health Organization recommends regular fish consumption (1-2 servings per week, equivalent to 200 to 500 mg/day EPA + DHA) as protective against coronary heart disease and ischaemic stroke.
Fish oil is FDA approved to lower triglycerides levels, but it is also used for many other conditions. It is most often used for conditions related to the heart and blood system. Some people use fish oil to lower blood pressure, triglycerides and cholesterol levels. Fish oil has also been used for preventing heart disease or stroke, as well as for clogged arteries, chest pain, irregular heartbeat, bypass surgery, heart failure, rapid heartbeat, preventing blood clots, and high blood pressure after a heart transplant.