BModerate evidence, real but modestOther
The short answer
The heart-protection story is weaker than it was in 2010 and stronger than the sceptics allow. Reasonable if you do not eat fish. Two portions of oily fish beats a capsule.
Who this is actually for
People who eat oily fish less than about twice a week, and people with high triglycerides under medical supervision.
What it is legally allowed to claim
Nothing. There is no authorised EU health claim for this substance, so any packet promising a specific benefit is making a claim it is not entitled to make. That is worth knowing before you judge the price.
How much is too much
EFSA considers up to 5 grams per day of combined EPA and DHA safe for adults.
Cautions and interactions
High doses may increase bleeding risk. Tell your doctor before surgery and ask if you take an anticoagulant or antiplatelet.
Ask a pharmacist before you start anything. Interactions with prescribed medicines are the most common way supplements cause harm, and they are easy to check. Bring the actual packet, or a photo of the ingredients panel, because doses and forms vary enormously between products. Nothing here is a substitute for advice about your own situation.