Omega-3 Side Effects

Generic Name: omega-3 polyunsaturated fatty acids

Note: This page contains side effects data for the generic drug omega-3 polyunsaturated fatty acids. It is possible that some of the dosage forms included below may not apply to the brand name Omega-3.

It is possible that some side effects of Omega-3 may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to omega-3 polyunsaturated fatty acids: oral capsule liquid filled

As well as its needed effects, omega-3 polyunsaturated fatty acids (the active ingredient contained in Omega-3) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking omega-3 polyunsaturated fatty acids, check with your doctor immediately:

Incidence not known
  • Bleeding gums
  • cough
  • coughing up blood
  • difficulty with breathing or swallowing
  • dizziness
  • fast or irregular heartbeat
  • headache
  • hives, itching, or skin rash
  • increased menstrual flow or vaginal bleeding
  • nosebleeds
  • paralysis
  • prolonged bleeding from cuts
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • red or black, tarry stools
  • red or dark brown urine
  • sweating
  • tightness in the chest
  • unusual tiredness or weakness

Some omega-3 polyunsaturated fatty acids side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common
  • Acid or sour stomach
  • bad, unusual, or unpleasant (after) taste
  • belching
  • bloated or full feeling
  • change in taste
  • excess air or gas in the stomach
  • heartburn
  • indigestion
  • stomach discomfort, upset, or pain
Incidence not known
  • Diarrhea
  • difficulty having a bowel movement (stool)
  • loss of appetite
  • nausea or vomiting
  • passing of gas
  • stomach fullness

For Healthcare Professionals

Applies to omega-3 polyunsaturated fatty acids: oral capsule, oral delayed release capsule, oral liquid, oral tablet chewable


Gastrointestinal side effects including eructation (4.9%), dyspepsia (3.1%), anorexia, constipation, dry mouth, dysphagia, colitis, fecal incontinence, gastritis, gastroenteritis, gastrointestinal disorder, increased appetite, intestinal obstruction, melena, pancreatitis, tenesmus, and vomiting have been reported.[Ref]


General side effects including infection (4.4%), flu syndrome (3.5%), back pain (2.2%), pain (1.8%), enlarged abdomen, asthenia, body odor, chest pains, chills, suicide, fever, generalized edema, fungal infection, malaise, neck pain, sudden death, and viral infection have been reported.[Ref]


Other side effects including taste perversion (2.7%) and lymphadenopathy have been reported.[Ref]


Dermatologic side effects including rashes (1.8%), alopecia, eczema, pruritus, and sweating have been reported.[Ref]


One study concluded that omega-3 fatty acid supplementation reduced heart rate and QRS duration in heart transplant recipients who were presumably devoid of vagal intervention. These findings suggest that omega-3 fatty acids may modify the electrophysiologic properties of the myocardium itself.[Ref]

Cardiovascular side effects including angina pectoris (1.3%), arrhythmia, bypass surgery, cardiac arrest, hyperlipidemia, hypertension, migraine, myocardial infarct, myocardial ischemia, occlusion, peripheral vascular disorder, syncope, and tachycardia have been reported.[Ref]


Musculoskeletal side effects including rheumatoid arthritis, arthralgia, arthritis, myalgia, pathological fracture, and tendon disorder have been reported.[Ref]


Metabolic side effects including edema, hyperglycemia, increased ALT and increased AST have been reported.[Ref]

Nervous system

Nervous system side effects including depression, dizziness, emotional lability, facial paralysis, insomnia, vasodilation, and vertigo have been reported.[Ref]


Respiratory side effects including asthma, bronchitis, increased cough, dyspnea, epistaxis, laryngitis, pharyngitis, pneumonia, rhinitis, and sinusitis have been reported.[Ref]


Genitourinary side effects including cervical disorder, endometrial carcinoma, epididymitis, and impotence have been reported.[Ref]


Hypersensitivity side effects including anaphylactic reaction have been reported.


Oncologic side effects including neoplasm and central nervous system neoplasia have been reported.[Ref]


Ocular side effects including cataract have been reported.[Ref]


Hematologic side effects including hemorrhagic diathesis have been reported.


1. "Product Information. Omacor (omega-3 polyunsaturated fatty acids)." Abbott Pharmaceutical, Abbott Park, IL.

2. "Product Information. Sea-Omega 30 (omega-3 polyunsaturated fatty acids)." Watson Pharmaceuticals, Corona, CA.

3. Harris WS, Gonzales M, Laney N, Sastre A, Borkon AM "Effects of omega-3 Fatty acids on heart rate in cardiac transplant recipients." Am J Cardiol 98 (2006): 1393-5

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