Evening primrose oil is derived from the seeds of Oenothera biennis and other species.
Evening primrose oil contains gamma-linolenic acid (GLA) and linoleic acid. Starflower oil (borage oil) and blackcurrant oil are also used as sources of GLA in dietary supplements. Evening primrose oil contains 8–11% GLA. Starflower oil contains 20–25% GLA, but the biological activity of starflower oil may be no greater than that of evening primrose oil, i.e. on a weight-for-weight basis, starflower oil has not been proved to be twice as active as evening primrose oil. Blackcurrant oil contains 15–25% GLA.
GLA is not an essential dietary component. It is normally synthesised in the body by the action of delta-6-desaturase on linoleic acid (obtained in the diet from vegetable and seed oils, e.g. sunflower oil).
GLA is a precursor of dihomogamma-linolenic acid (DGLA) and the series 1 prostaglandins (PG), and also of arachidonic acid (see Figure 1). Most of the DGLA formed from GLA is metabolised to PG1s; conversion of DGLA to arachidonic acid is very slow. Arachidonic acid is normally obtained from meat in the diet.
Supplementation with GLA increases the ratio of DGLA to arachidonic acid. DGLA levels are elevated to a greater extent by the administration of GLA than by the administration of linoleic acid (for reasons that are not entirely clear).
Prostaglandin PGE1 (produced from DGLA) inhibits platelet aggregation and is also a vasodilator; it has less potent inflammatory effects than prostaglandins of the PG2 series, thromboxane A2 and series 4 leukotrienes (produced from arachidonic acid).
The efficacy of GLA is thus thought to be due, in part, to the increased production of PG1 series prostaglandins at the expense of PG2 series prostaglandins, thromboxane A2 and series 4 leukotrienes.
Patients with diabetes mellitus or eczema may be at risk of GLA deficiency. Despite some claims, there is little evidence that foods rich in saturated fat and sugar, drinking alcohol, stress, pollution, high blood cholesterol, ageing, viral infections and hormone imbalances lead to GLA deficiency.
Evening primrose oil is used widely as a dietary supplement for various disorders, including PMS, hypertension, asthma and angina. It is claimed to reduce blood cholesterol levels and to act as a slimming aid.
Disorders for which evening primrose oil has been tested in controlled clinical trials include atopic dermatitis, diabetic neuropathy, mastalgia and breast cysts, menopausal flushing, Reynaud’s phenomenon, rheumatoid arthritis, schizophrenia, Sjogren’s syndrome, ulcerative colitis and various cancers. Evening primrose oil is being investigated in a range of other disorders including multiple sclerosis and hyperactivity in children.
The efficacy of evening primrose oil in inflam-matory skin conditions such as eczema is difficult to judge, because several trials have shown improvements in both the treatment and placebo groups. However, results indicate that for efficacy, high doses and long-term treatment are necessary. Evening primrose oil may work in these conditions not only by supplying precursors of prostaglandins but also by supplying the essential fatty acids to maintain cell membranes.
A double-blind crossover study involving 99 patients showed improvement in symptoms of eczema with doses of 4–6 g daily of evening primrose oil in adults and 2 g daily in children.1 Another trial involving 25 patients showed that evening primrose oil (45 mg gamma-linolenic acid per capsule) improved symptoms of eczema. Although there was also an improvement in the placebo group, this was not as great as in the evening primrose oil group.2 A further double-blind crossover study showed no clinical benefit in the use of evening primrose oil for atopic eczema in a mixed group of adults and children.3 Adult doses in this study were 12 or 16 500-mg capsules each day. Another study in patients with chronic dermatitis of the hands3 showed no difference between the effects of evening primrose oil (12 500-mg capsules each day) or placebo (sunflower oil capsules). Similarly conflicting results have been found in studies in children.4, 5
A double-blind RCT investigated the possible preventive effect of GLA supplementation on the development of atopic dermatitis in infants at risk. One hundred and eighteen formula-fed infants with a maternal history of atopic disease received borage oil supplement (100 mg GLA) or sunflower oil supplement for the first 6 months of life. The intention-to-treat analysis showed a favourable trend for severity of atopic dermatitis associated with GLA supplementation, but no significant effects in the other atopic outcomes, including serum immunoglobulin E (IgE). The authors concluded that early supplementation with GLA in children at high familial risk does not prevent the expression of atopy, but it tends to alleviate the severity of atopic dermatitis in later infancy in these children.6
Premenstrual syndrome and the menopause
Evening primrose oil has been studied for its effect on the physical and psychological symptoms of PMS in some women. However, few good studies have been carried out. A review of four studies7 concluded that evening primrose oil is effective for the treatment of PMS. However, another study in 38 women8 showed no differences between the effect of placebo and evening primrose oil on symptoms such as fluid retention, breast pain or swelling or mood changes.
Some trials with evening primrose oil in cyclical mastalgia and breast tenderness have shown positive results.9, 10 However, the response can be slow, and it can take several months to decide whether or not treatment is successful. A recent study in 555 women with moderate to severe mastalgia found that GLA (Efamast) efficacy did not differ from that of placebo fatty acids and the presence or absence of antioxidant vitamins made no difference.11
Trial data on the effects of evening primrose oil during the menopause are conflicting. In one of the most recent studies,12 involving 56 post-menopausal women suffering hot flushes, gamma-linolenic acid offered no benefit over placebo.
Results from trials with evening primrose oil in rheumatoid arthritis have been mixed. In one study of 20 patients, treatment with non-steroidal anti-inflammatory drugs (NSAIDs) was stopped and administration of evening primrose oil resulted in no significant changes in symptoms of arthritis.13 In another study involving 49 patients,14 treatment with evening primrose oil (equivalent to 540 mg GLA daily) or a combination of evening primrose oil and fish oil (450 mg GLA plus 240 mg eicosapen-taenoic acid) allowed for a significant reduction in dose of NSAIDs. However, another study in 20 patients15 who received either evening primrose oil or olive oil twice daily for 12 weeks, showed no significant differences in terms of prostaglandin levels, therapeutic response or laboratory parameters. However, those individuals whose pro-inflammatory prostaglandin and thromboxane levels were reduced tended to have better therapeutic responses.
Encouraging findings have been reported with trials of evening primrose oil in diabetic neuropathy,16, 17 but not in asthma,18,19
hypercholesterolaemia,20 , 21 or obesity.22 Recent studies have also been conducted into the potential benefit of GLA in dry eye syndrome and periodontal disease. A preliminary study in 26 patients found that GLA, or linoleic acid, or tear substitutes reduced ocular surface inflammation and improved dry eye syndrome.23 In a small study involving 30 adults with periodontitis, GLA was found to have beneficial effects, which were more impressive than those for omega-3 fatty acids and lower doses of the two supplements in combination.24 Further studies will be necessary to more fully assess the potential of GLA in these conditions.
Evening primrose oil should be avoided in patients with epilepsy and in those taking epileptogenic drugs, e.g. phenothiazines. There is some evidence that GLA may increase the risk of seizures in these patients.25
Pregnancy and breast-feeding
Caution should be used in pregnancy (because of possible hormonal effects). No problems have been reported in breast-feeding.
Toxicity appears to be low. The only adverse effects reported are nausea, diarrhoea and headache. However, one report26 has warned of a potential risk of inflammation, thrombosis and immunosuppression due to slow accumulation of tissue arachidonic acid after prolonged use of GLA for more than 1 year.
Phenothiazines: increased risk (small) of epileptic fits.
Evening primrose oil and other supplements containing GLA are generally available in the form of capsules.
Symptomatic relief of eczema: 320–480 mg (as GLA) daily; child 1–12 years, 160–320 mg daily.
Symptomatic relief of cyclical and non-cyclical mastalgia: 240–320 mg (as GLA) daily for 12 weeks (then stopped if no improvement).
Dietary supplements provide 40–300 mg (as GLA) per daily dose.
Note: doses are given in terms of GLA; evening primrose oil supplements are not iden-tical; they provide different amounts of GLA.
Results of clinical studies with gamma-linolenic acid (GLA) in skin conditions, including atopic dermatitis, as well as PMS and rheumatoid arthritis, have produced conflicting results. However, some individuals with these conditions do appear to benefit. Preliminary research indicates that GLA may be beneficial in diabetic neuropathy.
Wright S, Burton JL. Oral evening primrose seed oil improves atopic eczema. Lancet 1982; 2: 1120– 1122.
Schalin-Karrila M, Mattila L, Jansen CT. Evening primrose oil in the treatment of atopic eczema: effect on clinical status, plasma phospholipid fatty acids and circulating blood prostaglandins. Br J Dermatol 1987; 117: 11–19.
Bamford JT, Gibson RW, Renier CM. Atopic eczema unresponsive to evening primrose oil. J Am Acad Dermatol 1985; 13: 959–965.
Biagi PL, Bordoni A, Masi M. A long-term study on the use of evening primrose oil (Efamol) in atopic children. Drugs Exp Clin Res 1988; 14: 285–290.
Hederos CA, Berg A. Epogam evening primrose oil treatment in atopic dermatitis and asthma. Arch Dis Child 1996; 75: 494–497.
van Gool CJ, Thijs C, Henquet CJ, et al. Gamma-linolenic acid supplementation for prophylaxis of atopic dermatitis – a randomized controlled trial in infants at high familial risk. Am J Clin Nutr 2003; 77: 943–951.
Horrobin DF. The role of essential fatty acids and prostaglandins in the premenstrual syndrome. J Reprod Med 1983; 28: 465–468.
Khoo SK, Munro C, Battistutta D. Evening primrose oil and treatment of pre-menstrual syndrome. Med J Austr 1990; 153: 189–192.
McFayden IJ, Forrest AP, Chetty U. Cyclical breast pain – some observations and the difficulties in treatment. Br J Gen Pract 1992; 46: 161–164.
Steinbrunn BS, Zera RT, Rodriguez JL. Mastalgia – tailoring treatment to type of breast pain. Postgrad Med 1997; 102: 183–188.
Goyal A, Mansel RE, on behalf of the Efamast Study Group. A randomized multicenter study of gamolenic acid (Efamast) with and without antioxidant vitamins and minerals in the manage-ment of mastalgia. Breast J 2005; 11: 41–47.
`Chenoy S, Hussain S, Tayob Y, et al. Effect of oral gamolenic acid from evening primrose oil on menopausal flushing. BMJ 1994; 308: 501–503.
- Belch JJ, Ansell D, Madhock R, et al. The effects of altering dietary essential fatty acids on requirements for non-steroidal anti-inflammatory drugs in patients with rheumatoid arthritis. Ann Rheum Dis 1988; 47: 96–104.
- Hansen TM, Lerche A, Kassis V, et al. Treatment of rheumatoid arthritis with prostaglandin E1 pre-cursors cis-linoleic acid and gamma-linolenic acid. Scand J Rheumatol 1983; 12: 85–88.
- Janntti J, Seppala E, Vapaatalo H. Evening primrose oil and olive oil in the treatment of rheumatoid arthritis. Clin Rheumatol 1989; 8: 238–244.
- 16. Gamma-Linolenic Acid Multicenter Trial Group. Treatment of diabetic neuropathy with gamma-linolenic acid. Diabetes Care 1993; 16: 8–15.
- Jamal GA, Carmichael H. The effect of gamma-linolenic acid on human diabetic peripheral neuropa-thy: a double-blind placebo-controlled trial. Diabetic Med 1990; 7: 319–323.
- Ebden P, Bevan C, Banks J. A study of evening primrose seed oil in atopic asthma. Prostaglandins Leukot Essent Fatty Acids 1989; 35: 69–72.
- Stenius-Aarniala B, Aro A, Hakulinen A. Evening primrose and fish oil are ineffective as supplementary treatment of bronchial asthma. Ann Allergy 1989;
- Viikari J, Lehtonen A. Effect of evening primrose oil on serum lipids and blood pressure in hyperlipidemic subjects. Int J Clin Pharmacol Ther Toxicol 1986;
- Boberg M, Vessby B, Selenius I. Effects of dietary supplementation with n-6 and n-3 long-chain polyunsaturated fatty acids on serum lipopro-teins and platelet function in hypertriglyceridaemic patients. Acta Med Scand 1986; 220: 153–160.
- Haslett C, Douglas JG, Chalmers SR. A double-blind evaluation of evening primrose oil as an anti-obesity agent. Int J Obesity 1983; 7: 549–553.
- Barabino S, Rolando M, Camicione P, et al. Systemic linoleic acid and gamma-linolenic acid therapy in dry eye syndrome with an inflammatory component. Cornea 2003; 22: 77–101.
- Rosenstein ED, Kushner LJ, Kramer N, Kazandi-jan G. Pilot study of dietary fatty acid supple-mentation in the treatment of adult periodontitis. Prostaglandins Leukot Essent Fatty Acids 2003; 68: 213–218.
- Miller LG. Herbal medicines. Selected clinical con-siderations focusing on known or potential drug-herb interactions. Arch Intern Med 1998; 158: 2200–2211.
- Phinney S. Potential risk of prolonged gamma-linolenic acid use. Ann Intern Med 1994; 120, 692.