What does Evening Primrose Oil do?

The ingredient which makes Evening Primrose Oil such a winning choice as a supplement is its high content of polyunsaturated fatty acids; and specifically gamma-linoleic acid(10).

Interestingly evening primrose oil has a 74% content of linoleic acid and actually only 9% gamma-linoleic acid (GLA)- however the latter is considered the key active ingredient in the oil(11). This is due to the fact that it has one of the highest concentrations of this substance, whereas most herbs and plants do not contain any!

If you remember, polyunsaturated fatty acids (PUFAs) are fatty acids with a structure of double bonds, and this group includes both omega-3 and some
ga-6 compounds.

Omega 3 fatty acids are well known as fish oils and include compounds such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The health benefits of such fish oils are expansive and include reduction of cardiovascular disease risk factors, anti-inflammatory and anti-oxidant effects; reduction of depression; and disease modification in arthritis(12).

It is interesting then that evening primrose oil is so beneficial, even though it is predominantly made up of omega-6 fatty acids which generally are considered pro-inflammatory.

A lot of research has been undertaken to examine the effect of evening primrose oil (or its principle ingredient GLA) in rheumatoid arthritis (RA). This is a form of arthritis which is characterised by chronic joint inflammation secondary to overproduction of inflammatory chemicals and reduced oxidative joint defence mechanisms.

It has been shown that GLA-rich oils provide an effect which reduces not only inflammatory processes but also reduces antioxidant activity and reduces the growth of new blood vessels(13-14).

The activity of reactive oxygen species (free radicals) has been considered one of the provocative factors for autoimmune diseases such as RA. Consumption of evening primrose oil has been shown to be able to reduce inflammation and oxidative stress from free radicals; by increasing the amount and effectiveness of antioxidant enzymes, to the extent that disease activity in RA is reduced(14-15).

This would subsequently result in reduce symptoms (such as pain and stiffness) and better mobility and function in those suffering from RA.


Evening Primrose Oil –  Weight loss

The holy grail of supplements is weight loss aids. Anything we can consume which may assist the loss of body fat is likely to be often sold and used by the population!


However, once again despite people often singing the praises of evening primrose oil for this task, the benefits are not as clear and consistent as you may expect.

For example, a double-blind study on 100 significantly overweight women examined the benefit of evening primrose oil supplementation over 12-weeks and compared to a placebo supplement(19). This study showed no difference between groups, meaning evening primrose oil was only as effective as a placebo tablet. However, this trial was flawed methodologically by a 25% drop out rate which would substantially impact how legitimate and valid they results should be considered. This was also in a group of women who had failed to respond previously to other forms of treatment- leading them to be considered to have “refractory obesity”. Simply put this is a form of obesity which is considered to be resistant to treatment(20).

Another study (double blind randomised trial) examined whether evening primrose oil therapy may have an influence only on those who had a family history of obesity(21). These results indicated a significant loss of weight in those who did have a family history; particularly if both parents were obese. This perhaps indicates a true genetic component on the likely effectiveness of evening primrose oil on weight loss.

Considering the two sides of seemingly confusing results from this evidence, it is clear that more research is necessary to determine whether evening primrose oil is really useful for weight loss.


Evening Primrose Oil –  Migraines


A final area where evening primrose oil is often used as therapy is with headaches, and specifically with migraines.

Previously a different ingredient of evening primrose oil (phenylalanine) has been considered the most important factor in its proposed effects on migraines.

However, a study on 129 participants over a 6 month period examined the benefits of PUFA consumption(22).

Of the 129 participants evaluated, 86% experienced a reduction in both headache frequency and length of the attack.

22% of those studied actually became free of migraines altogether. A group of 14% only, showed minimal or no improvement to the therapy.