Evening Primrose

Fever plant, king’s cure all, night willow-herb, Oenothera biennis, rock-rose, sand lily, scabish, sun-drop

Evening primrose oil is extracted from the seeds of Oenothera biennis. It contains the amino acid tryptophan and a high concentration of essential fatty acids, in particular cislinoleic acid (CLA) and gamma-linoleic acid (GLA). The variety of evening primrose grown for commercial purposes produces oil with 72% CLA and 9% GLA. These fatty acids are prostaglandin precursors.

Conversion of the prostaglandin precursors into prostaglandins is the basis for using this oil to stimulate cervical ripening, prevent heart disease, and reduce symptoms of rheumatoid arthritis. Its efficacy in other clinical conditions may result from its supply of fatty acids. Evening primrose is available as capsules, liquid, oil, and tablets (evening primrose complex), in products such as Mega Primrose Oil, Original Primrose for Women, and Royal Brittany Evening Primrose Oil.

Reported uses

Used by midwives to stimulate cervical ripening during pregnancy at or near term and to ease childbirth. Also used to manage cyclic mastitis, premenstrual syndrome, and neurodermatitis. Used as a dietary stimulant. Used to treat eczema and diabetic neuropathy in Europe, although recent evidence doesn’t support its use for these conditions. Also used to treat hypercholesterolemia, rheumatoid arthritis, inflammatory bowel disease, Raynaud’s disease, Sjogren’s syndrome, chronic fatigue syndrome, endometriosis, obesity, prostate disease, hyperactivity in children, and asthma.


  • Oral use: Based on GLA content; typically, 1 to 2 capsules (0.5 to 1 g) three times a day
  • Cyclic mastitis: 3 g by mouth every day in 2 or 3 divided doses
  • Diabetic neuropathy: 4 to 6 g by mouth every day
  • Eczema in children: 2 to 4 g by mouth every day
  • Rheumatoid arthritis: 5 to 10 g every day.


Adverse reactions may include headache, nausea, diarrhea, bloating, vomiting, flatulence, and allergic reactions. When given with drugs that lower the seizure threshold such as tricyclic antidepressants, phenothiazines, and other epileptogenic drugs, there is an increased risk of seizures.

Those with an allergy to evening primrose oil and pregnant and breast-feeding patients should avoid use. Those with a history of epilepsy and those taking a tricyclic antidepressant, phenothiazine, or another drug that lowers the seizure threshold should also avoid use.

Clinical considerations

  • Monitor patient for allergic reaction.
  • The fatty oil, extracted from the seeds of the evening primrose plant by a cold extraction process, is available standardized for fatty acid content.
  • Drug effects may be delayed: patients with cyclic mastitis and premenstrual syndrome may not see improvement for 4 to 6 weeks, with maximum benefit in 4 to 8 months; those with eczema may experience decreased pruritus in 3 to 4 months; and patients with diabetic neuropathy may see improvement in 3 to 6 months.
  • Vitamin E may be given with evening primrose oil to prevent the formation of toxic metabolites.
  • Tell patient to discontinue the herb if they have signs or symptoms of an allergic reaction, such as trouble breathing, hives, itchy or swollen skin, or rash.
  • Advise patient to consult with her health care provider before using evening primrose oil during pregnancy or while breast-feeding.
  • Advise patient to take herb with food to minimize adverse GI reactions.
  • Tell patient to remind pharmacist of any herbal or dietary supplement that he’s taking when obtaining a new prescription.
  • Advise patient to consult his health care provider before using an herbal preparation because a conventional treatment with proven efficacy may be available.

Safety Risk The oil may unmask previously undiagnosed epilepsy, especially when taken with a drug that treats depression or schizophrenia.

Research summary

The concepts behind the use of evening primrose oil and the claims made regarding its effects haven’t yet been validated scientifically.

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