Triglyceride lowering scales with dose
The best-established effect of fish oil is on blood triglycerides, and it is dose-dependent: larger combined EPA plus DHA doses produce greater triglyceride reductions, with meaningful effects generally seen from a few grams per day and continuing up toward roughly 4 grams per day. At prescription-level doses the reduction can be substantial, especially in people who start with high triglycerides.
This is why high-dose omega-3 preparations are used clinically for severely elevated triglycerides, whereas typical over-the-counter capsules deliver much smaller EPA and DHA amounts per serving than the label's total fish-oil weight suggests.
Cardiovascular outcomes are less settled
The relationship between omega-3 dose and cardiovascular event reduction is more complex and the trial evidence has been mixed. Some high-dose trials reported benefit while others did not, and results have depended on the formulation, dose, and population studied. Triglyceride lowering is therefore better characterised than any guaranteed reduction in heart attacks or strokes.
High doses can increase bleeding risk and may interact with anticoagulants. This is general educational information, not medical advice; dosing decisions should be made with a qualified clinician.