Food Supplements and Vitamins. Evening primrose oil (Oenothera biennis L.)



Evening primrose oil (EPO) contains an omega-6 essential fatty acid, gamma-linolenic acid (GLA), which is believed to be the active ingredient. EPO has been studied in a wide variety of disorders, particularly those affected by metabolic products of essential fatty acids. However, high-quality evidence for its use in most conditions is still lacking.


NB! The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (18 years and older)

Studies in the treatment of eczema have used doses of 4 to 8 grams of evening primrose oil (EPO) daily, taken by mouth, divided into several smaller doses throughout the day. Studies treating breast pain have used doses of 3 grams EPO daily, taken by mouth, divided into several smaller doses throughout the day.

Children (younger than 18 years)

Studies in children treated for skin conditions have used 3 grams of evening primrose oil daily, taken by mouth, divided into several smaller doses throughout the day. It is reported that the maximum dose should not be greater than 0.5 gram per kilogram of body weight daily. Medical supervision is required.


NB!  There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.


Allergy or hypersensitivity to evening primrose oil has not been widely reported. Individuals with allergy or adverse reactions to plants in the Onagraceae family, gamma-linolenic acid, or other ingredients in evening primrose oil should avoid its use. Contact dermatitis (skin rash) is possible.

Side Effects and Warnings

Several reports describe seizures in individuals taking evening primrose oil (EPO). Some of these seizures developed in people with a previous seizure disorder, or in individuals taking EPO in combination with anesthetics. Based on these reports, people with seizure disorders should not take EPO. EPO should be used cautiously with drugs used to treat mental illness such as chlorpromazine (Thorazine®), thioridazine (Mellaril®), trifluoperazine (Stelazine®), or fluphenazine (Prolixin®), due to an increased risk of seizure. Patients who plan to undergo surgery requiring anesthesia should stop taking EPO two weeks ahead of time because of the possibility of seizure.

Other reports describe occasional headache, abdominal pain, nausea, and loose stools in people taking EPO. In animal studies, gamma-linolenic acid (an ingredient of evening primrose oil) is reported to decrease blood pressure. Early results in human studies do not show consistent changes in blood pressure.

Pregnancy and Breastfeeding

There is not enough information to recommend the safe use of evening primrose oil during pregnancy or breastfeeding.



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