Taking fish oil for 90 days can produce several changes in the body, mainly because fish oil contains omega-3 fatty acids, especially:
EPA (eicosapentaenoic acid)
DHA (docosahexaenoic acid)
These fats become incorporated into cell membranes and influence inflammation, blood fats, blood vessels, the brain, and immune function. The effects vary depending on your diet, health status, the dose you take, and the quality of the supplement.
Below is a detailed look at what may happen during a 90-day period.
Days 1–7: The Body Starts Absorbing Omega-3s
1. Omega-3 levels begin increasing
After you start taking fish oil, EPA and DHA enter your bloodstream and gradually become stored in:
Red blood cells
Cell membranes
Brain tissue
Heart tissue
Immune cells
Your body does not change overnight because omega-3s need time to build up.
2. Possible early side effects
Some people notice:
Fishy burps
Fish taste in the mouth
Mild stomach discomfort
Loose stools
Bloating
Nausea
These effects are more common with larger doses or lower-quality supplements.
Tips to reduce side effects:
Take fish oil with meals
Split the dose between breakfast and dinner
Keep capsules refrigerated
Choose purified, enteric-coated products
Weeks 2–4: Changes in Inflammation and Blood Chemistry
1. Lower inflammation signals
EPA and DHA can reduce the production of certain inflammatory molecules.
Possible effects:
Less joint stiffness
Reduced muscle soreness after exercise
Improved recovery after physical activity
This is more noticeable in people who have higher inflammation levels.
2. Blood triglycerides may decrease
One of the strongest proven effects of fish oil is lowering triglycerides, a type of blood fat.
After several weeks, higher doses of EPA/DHA may reduce triglycerides significantly.
Benefits may include:
Improved blood lipid profile
Reduced risk factors associated with cardiovascular disease
However, fish oil is not a replacement for cholesterol medication when medication is medically needed.
3. Blood becomes slightly less prone to clotting
Omega-3s can affect platelet activity, meaning blood cells involved in clot formation.
Possible effects:
Slightly reduced platelet stickiness
Improved blood vessel function
At normal supplement doses, this is usually not a problem, but people taking blood-thinning medicines should discuss fish oil use with a healthcare professional.
Weeks 4–8: Brain, Mood, and Nervous System Effects
1. Brain cell membrane changes
DHA is a major structural component of brain cells.
Over time, increased DHA availability may support:
Brain cell communication
Memory processes
Nervous system function
Research suggests omega-3 intake may be associated with better cognitive health, especially in people with low omega-3 intake.
2. Possible mood effects
Some studies suggest EPA-rich fish oil may support mood regulation.
Potential benefits:
Improved emotional balance
Reduced symptoms of low mood in some people
Effects are not guaranteed and depend on individual factors.
Weeks 8–12 (Around 90 Days): More Noticeable Long-Term Effects
After approximately three months, omega-3 levels in the body are usually more stable.
Possible changes include:
1. Heart and Blood Vessel Benefits
Fish oil may help:
Improve triglycerides
This is the most established cardiovascular effect.
Support blood vessel function
Omega-3s may help blood vessels relax and respond better.
Slightly reduce blood pressure
Some people experience small reductions, especially those with high blood pressure.
Support normal heart rhythm
Omega-3s influence electrical activity in heart cells, although their role in preventing heart rhythm problems is complex.
2. Joint Health
People with inflammatory joint conditions may notice:
Less morning stiffness
Reduced joint tenderness
Less need for some pain medication (in some cases)
Fish oil does not rebuild cartilage or cure arthritis, but it may help regulate inflammation.
3. Skin and Hair Effects
Omega-3s contribute to healthy skin barriers.
Possible effects after several months:
Skin:
Less dryness
Better moisture retention
Reduced irritation in some people
Hair:
Improved scalp health
Reduced dryness-related breakage
Fish oil does not directly cause new hair growth, but improved nutrition may support healthier hair.
4. Exercise and Muscle Recovery
For active people, fish oil may help:
Reduce exercise-related inflammation
Reduce delayed muscle soreness
Support muscle protein balance
The effect is usually modest and works best alongside:
Adequate protein intake
Strength training
Good sleep
5. Eye Health
DHA is an important component of the retina.
Adequate DHA intake supports:
Normal vision function
Eye cell health
Fish oil may be useful for people who have low omega-3 intake, although it is not a guaranteed treatment for eye diseases.
What Happens to Cholesterol After 90 Days?
Fish oil affects different blood fats differently.
Triglycerides:
✅ Usually decrease
HDL (“good cholesterol”):
↗ May slightly increase
LDL (“bad cholesterol”):
⚠ May stay the same or sometimes increase slightly, especially with certain high-dose formulations
The overall effect depends on the person and the type of fish oil used.
Possible Negative Effects After 90 Days
Most people tolerate fish oil well, but possible issues include:
Digestive problems
Burping
Heartburn
Diarrhea
Nausea
Increased bleeding tendency
Higher doses may increase bleeding risk, especially with:
Warfarin
Aspirin
Clopidogrel
Other blood-thinning medicines
Vitamin A or D toxicity (mainly from cod liver oil)
Regular fish oil is different from cod liver oil.
Cod liver oil can contain high amounts of:
Vitamin A
Vitamin D
Too much vitamin A can be harmful.
How Much Fish Oil Is Usually Taken?
Amounts are usually discussed in terms of EPA + DHA, not the total amount of oil.
Common ranges:
General health:
About 250–500 mg EPA + DHA per day
High triglycerides:
Often 2–4 grams EPA/DHA per day under medical supervision
A capsule labeled “1,000 mg fish oil” may contain only about 300 mg EPA + DHA, depending on the product.
What You May Notice After 90 Days (Summary)
Area Possible Change
Blood triglycerides Lower levels
Inflammation Reduced inflammatory activity
Joint comfort Less stiffness for some people
Heart health Better blood vessel function
Brain Supported nerve cell function
Mood Possible improvement in some people
Skin Less dryness
Exercise recovery Less soreness
Eyes Supports retinal health
Side effects Fish burps, stomach issues
Who Should Be Careful Before Taking Fish Oil?
Talk with a healthcare professional before high-dose fish oil if you:
Take blood thinners
Have a bleeding disorder
Have surgery planned
Have fish or shellfish allergies
Have heart rhythm conditions
Are pregnant and considering high doses
Bottom line
After 90 days of consistent fish oil use, the most reliable changes are usually higher omega-3 levels in your body, lower triglycerides (especially at therapeutic doses), and reduced inflammatory activity. Other benefits—such as better joints, mood, skin, and exercise recovery—may occur but vary widely between individuals. The biggest impact is usually seen in people who previously had low omega-3 intake or higher inflammation levels.