Evening Primrose Oil

General Information

Common Name:
Evening Primrose Oil (abbreviated EPO)

Latin Name:

Oenothera biennis L.



Other Names:

King’s Cure-All

Indications & Historical Uses

For centuries, native American tribes have used evening primrose both as a food and a remedy for a variety of ailments. In the seventeenth century, the plant was imported from North America and naturalized in Europe. For the last three centuries, folk healers have used evening primrose to treat myriad ailments. Infusions made from the entire evening primrose plant were used as an astringent for the skin and as a treatment for anxiety, stomach and intestinal disorders, asthma and whooping cough. Poultices made from the evening primrose plant were used externally to encourage wound healing.

The healing properties of the evening primrose plant are still recognized today; however, research has revealed that it is the small, reddish seed of the evening primrose that endows the plant with its biological activity. Modern-day herbalists and health-care practitioners recommend the oil extracted from the small, reddish seeds of the evening primrose plant for use in therapeutic herbal preparations. Evening primrose oil (EPO) is currently recognized as being beneficial for use in:

  • Treatment of rheumatoid arthritis – –studies show that EPO may help reduce or eliminate requirement for non-steroidal anti-inflammatory medications.
  • Treatment of inflammatory skin diseases (e.g. eczema,psoriasis) – research indicates that ingestion of EPO and/or topical use of EPO (i.e. application of contents of capsule to the skin) can relieve itching and eliminate the need for use of anti-inflammatory steroidal medications; safe for use in children and adults.
  • Treatment and prevention of heart disease and stroke; helps to reduce blood pressure – EPO has been shown to reduce blood cholesterol levels by an average of 31.5% and it additionally helps to reduce platelet aggregation (i.e. prevents blood clot formation)
  • Treatment and prevention of PMS symptoms such as bloating, breast tenderness, depression, irritability, headaches, etc.
  • Improves skin condition – helps to produce and maintain healthy condition of skin
  • Helps to reverse neurologic damage of advanced diabetes and aids in the normalization of certain lipid metabolic factors involved in the disease process of diabetes
  • Treatment of ulcerative colitis
  • Treatment of symptoms of multiple sclerosis – EPO has been shown to help treat the symptoms of MS; many trials are currently underway to help quantify its usefulness for patients suffering from MS
  • Treatment of breast pain, for example, in conditions such as fibrocystic breast disease
  • Helps to reduce symptoms of alcohol withdrawal and to increase speed of liver healing following liver damage due to chronic use of alcohol or medications
  • Helps to kill tumor cells in test tube and live animal studies – studies are currently underway to identify which human cancers are most susceptible to the effects of EPO
  • Helps to reduce and retard hair loss (seen in alopecia and male pattern baldness)
  • Treatment of infertility, especially in men
  • Helps to strengthen immune system function
  • Raynaud’s phenomenon
  • Sjogren’s syndrome
  • Menopausal flushing spells

Contraindications & Precautions

None known. See Caution.

None. See Caution.

Adverse Side Effects:
None known. Numerous toxicity studies have shown that EPO is a very safe herbal medication with a sound safety profile. See Caution.

Drug Interactions:
No significant interactions preclude the use of EPO. However, black currant and borage oils are known to have similar effects to EPO, so it is important to adjust the dosage of EPO if taking these herbal medications simultaneously. Also, EPO is known to reduce blood clotting activity, so it is best to consult a physician before taking EPO in conjunction with other anticoagulants(blood thinning medications). Rare possibility of seizures in patient’s with schizophrenia treated with phenothiazine drugs and evening primrose oil. See Caution.

Dosage Information

How Supplied:

  • Capsule (liquid filled) (Bionutrix formulation is a liquid-filled capsule.);
  • Liquid;
  • Oil;
  • Tablet.


The recommended dosage is 500mg taken up to three times per day. The disorder one wishes to treat or prevent may lead to some variation in the recommended dose or dosing schedule. Instructions for common ailments or conditions are as follows:

For PMS:
A dosage of 500 mg EPO taken up to three times per day is recommended; should be taken 2 to 3 days before the expected onset of symptoms (i.e. usually 10 days before the onset of menstruation).

For cardiovascular or inflammatory disorders:
A daily dosage of 500mg to 1000mg per day of EPO (containing between 1g to 2g of GLA) is recommended.

For eczema:
For atopic eczema, a smaller daily dosage of 250mg to500mg per day of EPO (approximately equivalent to 250mg to 500mg of GLA) is recommended.


The seeds of the evening primrose plant are comprised of about 14% of a particular oil (evening primrose oil, EPO) which has a fixed composition. Evening primrose oil contains a high concentration of essential fatty acids (EFAs), the most important of which are the essential polyunsaturated fatty acids known as gamma-linoleic acid (GLA) and cis-linoleic acid. EPO contains about 7 to 10% GLA and 50 to 70% cis-linoleic acid. When ingested, gamma-linoleic acid is converted to a precursor form of the hormones known as prostaglandins. These hormones serve a variety of biological functions, ranging from mediating inflammatory processes to moderating pain sensations and influencing blood clotting processes. The myriad functions of prostaglandins and the involvement of EPO in prostaglandin metabolism confer a wide variety of therapeutic properties upon the evening primrose seed. See Indications and Historical Uses (above) for a comprehensive list of uses for EPO. Essential fatty acids, and GLA in particular, are required to maintain a healthy heart, as well as healthy skin, blood vessels, joints and various other healthy organs. The human body cannot manufacture essential fatty acids from any other compounds; therefore, EFAs must be obtained from dietary sources or supplements which contain ready-made EFAs. EPO capsules are one such source of EFAs. Gamma-linoleic acid is one of the most biologically important EFAs, and most people usually manufacture it as needed from ingested cis-linoleic acid. However, GLA itself is not available in significant quantity in any particular food, and it is for this reason that evening primrose oil is recommended as a supplement for people who would benefit from larger, therapeutic quantities of GLA and for people who have a metabolic defect which prevents them from converting cis-linoleic acid into GLA(e.g. in patients with atopic eczema). Factors such as stress, aging, high cholesterol, alcohol, diabetes, PMS, viral infections, and other conditions may interfere with the normal conversion of linolenic acid into GLA. In these conditions the patients would benefit from larger therapeutic doses of evening primrose oil-a rich source of GLA. Many studies have verified the effectiveness of EPO as a medicinal herb. EPO has the added advantage of being a very safe preparation – toxicity studies have shown that it has a solid safety profile when used at recommended therapeutic dosages. However, it is important to purchase EPO from a reliable manufacturer of herbal preparations, since a 1991 study has shown that most North American preparations contain no evening primrose oil at all, being comprised instead of pure safflower oil. It is therefore imperative to verify that the manufacturer has dose-standardized the EPO preparation and can guarantee that all capsules contain at least the minimum therapeutic dose of gamma-linoleic acid and/or evening primrose oil.

Active Ingredients:

The evening primrose seed contains 14% evening primrose oil, of which 7 to 10% is gamma-linoleic acid (GLA) and 50-70% is cis-linoleic acid. Both GLA and cis-linoleic acid are essential fatty acids (EFAs). Evening primrose oil also contains other EFAs, which further contribute to its biological activity. The human body cannot manufacture EFAs, and these must therefore be obtained from the diet or from supplements such as EPO capsules. EFAs are required to maintain a healthy heart, as well as healthy skin, blood vessels, joints and various organs.

Enhancing Agents:

None known.


The evening primrose is a wildflower native to eastern North America. Despite its common name, it is not a true primrose. It is, however, a member of the primrose family, Onagraceae. This hardy plant grows in dry, sandy or stony soil and is commonly found in waste sites, on sandy dunes and near railway embankments. The plant grows to a height of about three to four feet, with lance-shaped, hairy leaves and large, attractive, four-petal lemon yellow flowers which bloom along the length of a branched reddish stem ending in a spike at the apical tip. The plant derives its name from the odd behaviour of the flowers, which open only at night. The flower blooms from mid-to late summer, at which point the blooms fall off. The blooms are then replaced by tubular, pointed seed pods which house small, reddish seeds containing an oil rich in a number of essential fatty acids (EFA’s), most notably gamma-linoleic acid (GLA) and and cis-linoleic acid. It is the properties of the EFA’s which give the evening primrose its biological activity; therefore, the seeds of the plant are used to produce the medicinal herbal extract


The small, reddish seeds of the evening primrose plant are harvested from the tubular, pointed seed pods of the mature plant in the mid- to late summer, when they contain a peak concentration of EFA’s. The large, pale yellow flowers fall off of the plant during the summer, and they are then followed by the tubular, pointed seed pods. Bionutrix harvests the seeds from the tubular pods of special, organically-grown wild evening primrose plants in late summer, when they are of peak potency. The seeds are carefully-extracted and crushed and then subjected to extraction in a special, organically-derived safflower oil-based medium designed to extract and dissolve all of the EFA’s which give the plant its therapeutic properties. This EFA-rich liquid is then spectrographically-analyzed to determine the concentration, which is then standardized for GLA. The precisely-standardized oil-based formulation is then encapsulated in a non-reactive gelatin capsule in 250mg doses of EPO. Bionutrix produces the most reliably dose-standardized, purest and most potent organic extract of evening primrose oil and encapsulates it in an easy-to-swallow, soft gelatin capsule. All Bionutrix capsules are guaranteed to contain a precisely-standardized therapeutic dose of EPO in a hypo-allergenic medium of organic safflower oil.

Scientific References

American Pharmaceutical Association. Handbook of Nonprescription Drugs. 11th ed. Washington,D.C.: American Pharmaceutical Association.

Belch, J.J., et al. Annals of the Rheumatic Diseases, 47(2)(1988):96-104.

Berth-Jones, J. and Graham-Brown, R.A. The Lancet, 341(8860)(1993):1557-60.

Biagi, P.L., et al. Drugs Under Experimental and Clinical Research, 14(4)(1988):285-90.

Field, E.F. The Lancet, 1(1978):780.

Gately, C.F., and Mansel, R.E. British Medical Bulletin, 47(1991):284.

Ghayor, T., and Horrobin, D.F. IRCS Medical Science, 9(1981):582.

Glen, I., et al. Alcoholism, Clinical and Experimental Research, 11(1987):37-41.

Greenfield, S.M., et al. Alimentary Pharmacology and Therapeutics, 7(2)(1993):159-66.

Horrobin, D.F. Journal of Reproductive Medicine, 28(7)(1983):465-68.

Horrobin, D.F. Medical Hypotheses, 5(1979):365.

Horrobin, D.F., and Manku, M.S. Paper presented at the annual meeting of the Intl. Conference on Oils, Fats and Waxes. Auckland, 1983.

Jamal, G.A. The Lancet, 1(1986):1098.

Joe, L.A. and Hart, L.L. Annals of Pharmacotherapy, 27(12)(1993):1475-77.

Kerscher, J.J., and Korting, H.C. Clinical Investigator, 70(2)(1992):167-71.

Lawrence Review of Natural Products. St.Louis: Facts and Comparisons, November 1993.

Leung, A.Y., and S.Foster. Encyclopedia of Common Natural Ingredients Used in Food, Drugs, andCosmetics. 2nd ed. New York: John Wiley & Sons, 1996.

Leventhal, L.J., et al. Annals of InternalMedicine, 119(9)(1993):867-73.

Mindell, E. Earl Mindell’s Herb Bible. New York: Simon and Schuster/Fireside, 1992.

Poulaka, J., et al. Journal of Reproductive Medicine. 30(1985):149

Ramesh, G., et al. Nutrition, 8(5)(1992):343-47.

Stewart, A. Journal of Reproductive Medicine, 32(6)(1987):435-41.

Takahashi, R., et al. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 49(2)(1993):569-71.

Traitler, H., et al. Lipids, 19(12)(1984):923-28

Trease, G.E., and W.C. Evans. Trease and Evans’ Pharmacognosy. 13th ed. Philadelphia: BailliereTindall, 1989.

Tyler, V.E. Herbs of Choice: The Therapeutic Use of Phytomedicinals. Binghampton, N.Y.:Haworth Press/Pharmaceutical Products Press, 1994.

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Wright, S. Acta Dermato-Venereologica. Supplementum, 114(1985):143-45.


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