Are There Side Effects of Cod Liver Oil?

When taken in moderation, cod liver oil doesn’t have any side effects, unlike many medicines. This is because cod liver oil is more akin to food, rather than medication. The ingredients in a natural cod liver oil are natural and in quantities that the body can naturally handle. However, there are still several things to consider, and although these are not side-effects per se, it is worth bearing the following in mind.

‘Side-effects’ of cod liver oil

  1. Cod liver oil does taste of fish. Some cod liver oils are de-oderised and heavily processed to reduce these flavours as much as possible, but always bear in mind that it is a fish oil, and it will have fishy flavours. If you are rather averse to fishy flavours you may experience nausea.
  2. As cod liver oils are fats, they can, like all fats, trigger heartburn.
  3. heartburn

    Cod liver oil is a natrual blood thinner, and so taking excessive amounts may cause problems (for example reduce blood clotting/ increasing bleed time). It may also interact with some medications that help thin the blood.
  4. Cod liver oil is naturally high in vitamin A, but some manufacturers concentrate the oil/ add vitamin A into the oil to increase the vitamin A content even further. Taking such an oil in large dosages/ along with other vitamin A supplements, or other sources high in vitamin A it can lead to a number of health problems. These can range from headaches to blurred vision as outlined here. Unlike many vitamins, vitamin A is toxic in large amounts and care should be taken with concentrated cod liver oils/ consuming multiple sources high in vitamin A.
  5. If you are allergic to fish, there is a possibility that you could have an allergic reaction to cod liver oil, although this is not always the case. If you know you are allergic to fish, it is best to speak to your doctor before taking fish oil.

Avoiding the ‘side-effects’ of cod liver oil

  1. If you simply just don’t really like the taste of cod liver oil many liquid products are flavoured which can mask the taste very well. However, you will still have to put up with a bit of a fishy taste and oil coating the mouth, which isn’t pleasant. If you suffer from nausea, then a flavour change may not be enough to help. A more effective solution is to take cod liver oil capsules, preferably with food. Capsules (and liquids) do sometimes give ‘repeating’ fishy flavours, which again, isn’t very pleasant. To minimise the risk of repeating flavours, it is best to consume cod liver oil with food, and use slow releasing capsules, such as those made from Algigel (seaweed/ gelatine).
  2. Taking cod liver oil will food can help eliviate the effects of heartburn. Slow release capsules can help even further.
  3. Taking cod liver oil in moderation will not cause any problems with thinning of the blood. However, if you are already taking prescription medication that thins the blood (e.g Asprin), then you should consult a doctor before taking cod liver oil.
  4. It is hard to take too much vitamin A, but if you take a lot of supplements it is possible. If you take cod liver oil in line with the guidelines, and try and avoid other supplements that contain vitamin A, there is no risk of vitamin A toxicity.


Cod liver oil is extremely safe to consume and has no major side effects. It only poses a potential health risk if you are allergic to fish, or take excessive amounts of concentrated cod liver oil. Being allergic to fish doesn’t mean that you are definitely allergic to cod liver oil, but you should be mindful that you could have an allergic reaction.

Other common side effects, such as nausea or heartburn, can be combated by taking cod liver oil with food/ in slow-release capsule form.

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