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Evening primrose oil (EPO)

Evenin primrose oil classification

EPO is rich in polyunsaturated omega-6 fatty acids that can help control pain and inflammation. Evidence for the effectiveness of EPO in reducing joint pain in rheumatoid arthritis isn’t conclusive, but there’s some evidence that it can improve morning stiffness. It doesn’t seem to alter long-term disease activity, so you should take it alongside your conventional therapy.

What is it?

Family: Herbal medicine of the Onagraceae family
Scientific name: Oenothera biennis
Other names: Tree primrose, fever plant, night willowherb, King’s-cure-all, scabish, scurvish, sun drop, suncups

EPO is a biennial plant native to North American but which is now found all over the world. The medicinal product is produced from the plant’s seeds. EPO capsules (500–1,300 mg) or oil (150 ml) are available from high-street retailers.

How does it work?

EPO contains 2–15% gamma-linolenic acid (GLA) and 70% linolenic acid (LA, which your body makes into GLA), which are types of polyunsaturated omega-6 essential fatty acids. GLA is important for maintaining a joint’s cell structure and function. Your body makes it into hormone-like substances called prostaglandins, which regulate your immune system and fight joint inflammation. GLA might also suppress inflammatory responses by directly acting on some inflammatory cells.

Several factors can interfere with your body’s production of GLA from LA, including: 

  • ageing
  • dietary deficiencies
  • viral infections
  • some diseases.

Sunflower oil and other oils generally used in normal diet contain only LA. EPO is one of the richest sources of pure GLA.

Is it safe?

No recommended safe doses have been found for the use in musculoskeletal conditions, but trials have used doses of 6 g (540 mg GLA) a day. If taken in the correct dose, EPO has no major safety problems.

Common side-effects include:

  • nausea
  • diarrhoea
  • rashes.

If you have epilepsy or seizure disorder you shouldn’t take EPO because it can cause seizures.
Interactions haven’t been well studied, but you should be cautious about using EPO if you take anti-inflammatory drugs (for example cortisone) and anticoagulants because interactions are possible.


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