The medicinal parts are the fatty oil extracted from the ripe seeds and the fresh plant gathered at the beginning of the flowering season.
Flower and Fruit
The fragrant flowers are 2 to 3 cm long and are solitary in the leaf axils. The open ones are lower than the buds. The sepals are lanceolate, acuminate, turned down, thin, pale green and smooth on the outside with a few scattered hairs. The petals are obovate. The ovary is inferior. The style has a 4-sectioned stigma. The fruit is a linear-oblong, quadrangular, downy-villous capsule up to 3 cm long. The seeds are 1.5 mm long, dark gray to black with irregular sharp edges.
Leaves, Stem, and Root
This biennial grows up to 1 m and has a spindle-shaped, fleshy, turniplike root, which produces leaf rosettes in the first year. The stem is erect, unbranched, or branched higher up and angular. The ovary is a capsule covered in short glandular hairs, with simple, light hairs on the purple papilla. The cauline leaves are short-petioled or sessile, often hanging, oblong-lanceolate, pointed, irregular, and finely dentate.
The flowers are fragrant and open in the evening.
Originally indigenous to North America, it is now naturalized throughout most of Europe and parts of Asia.
Evening Primrose oil is the fatty seed oil of Oenothera biennis. The oil is extracted by means of a cold-extraction process, which involves hexane in steel or glass-lined tanks. The extract is washed and the solvent removed using low pressure.
Fever Plant, King's Cureall, Night Willow-herb, Scabish, Sun Drop
Actions & Pharmacology
Fatty oil: chief fatty acids linoleic acid (65-80%), gamma-linolenic acid (8-14%), oleic acid (6-11%), palmitic acid (7-10%)
Evening Primrose oil (EPO) is an omega 6 fatty acid that contains approximately 8.9% gamma-linolenic acid (GLA). GLA is converted to dihomo-gamma-linolenic acid and then to prostaglandin E1 (PGE1) in vivo by the enzyme delta-6-desaturase. PGE1 has anti-inflammatory and cell membrane stabilizer activity in the body. Evening Primrose oil supplements provide increased levels of dihomo-gamma-linolenic acid in the blood of people with a deficiency of the enzyme delta-6-desaturase (Newall, 1996; Kershcer & Korting, 1992; Manku et al, 1982). GLA is also a component in breast milk, but is not added to infant formulas. It has been postulated that GLA may be beneficial to neural development in breast-fed infants (Newall, 1996; Makrides et al, 1995). Evening Primrose oil extracts exhibited antioxidant activity in a laboratory analysis (Birch et al, 2001). The oil has also shown positive action against diabetic neuropathy, hypercholesterolemia, hypertension, and irritable bowel syndrome (Keen et al, 1993; Guivernau et al, 1994; Viikari & Lehtonen, 1986; Leeds et al, 1990; Cotterell et al, 1990). Data is lacking, but Evening Primrose oil may prove effective in relieving the physical and psychological symptoms of PMS.
GLA may be a useful adjunct to primary tamoxifen treatment in endocrine-sensitive breast cancer; however, larger trials are needed to fully determine its role. Evening Primrose oil proved ineffective in the treatment of hepatic carcinoma (van der Merwe et al, 1990).
Positive effects of Evening Primrose oil on arthritis are not statistically evident.
Cervical Ripening Effects
Oral Evening Primrose oil was ineffective in reducing incidence of adverse labor outcomes and decreasing overall length of labor in low-risk nulliparous females (Dove D and Johnson P, 1999).
Evening Primrose oil can be considered a first-line treatment for cyclical breast pain. Since the response can be slow, treatment should be continued for several months before it is determined whether or not treatment is successful. As a second-line treatment, it does not appear useful (Steinbrunn et al, 1997; Holland & Gateley, 1994).
Evidence suggests that prostaglandins may have a role in pre-eclampsia. Although one trial indicates the usefulness of Evening Primrose oil to prevent pre-eclampsia, a second trial indicates it is not effective in decreasing existing pre-eclampsia (D'Almeida et al, 1992; Moodley & Norman, 1989).
A high dose of Evening Primrose oil and long-term treatment are necessary for anti-inflammatory results to occur in the skin. Evening Primrose oil may supply the appropriate essential fatty acids necessary to maintain cell membranes, as well as act as a precursor to prostaglandins.
Evening Primrose oil reduced platelet aggregation, thromboxane production, and increased bleeding time in 12 hyperlipidemic males (Guivernau et al, 1994).
Many studies investigating the efficacy of EPO in various diseases lack statistical significance yet report beneficial effects. It is unclear if the lack of statistical significance is due to a true lack of efficacy or an inadequate dose and/or time trial of a particular study.
Evening Primrose oil was able to decrease the use of nonsteroidal anti-inflammatory drugs (NSAIDs) in patients with rheumatoid arthritis. In this double-blind, placebo-controlled trial, 49 patients received either 12 capsules per day of Evening Primrose oil (540 mg of GLA), 12 capsules per day of a combination of Evening Primrose oil and fish oil (450 mg GLA and 240 mg eicosapentaenoic acid), or 12 placebo capsules per day (liquid paraffin). Treatment lasted for 12 months and was followed by three months of placebo for all patients. After three months of treatment, patients were asked to decrease their use of NSAIDs but to maintain their level from 12 to 15 months. There was a significant reduction in the dose of NSAIDS used by both the Evening Primrose oil group (p<0.003) and the Evening Primrose oil plus fish oil group (p<0.002). No significant changes were seen in clinical or laboratory measurements in the study. The subjective improvement was also higher in the two treatment groups compared to placebo (Belch et al, 1988).
Thirty-eight females with locally advanced or metastatic breast cancer receiving 2.8 g of GLA daily in addition to tamoxifen 20 mg once daily experienced significantly (p=0.016) quicker initial tumor response at 6 weeks of treatment when compared to patients taking only tamoxifen 20 mg once daily. Change in tumor size, estrogen receptor (ER), and bcl-2 protein expression were used to determine tumor response. Follow-up for the study was not long enough to determine if addition of GLA conferred a longer duration of tumor response to treatment (Kenny et al, 2000).
Evening Primrose oil improved neurophysiological and neurological measures in patients with diabetic polyneuropathy. A one-year, multicenter, randomized, double-blind, placebo-controlled parallel study was conducted with 111 patients who had mild diabetic neuropathy. Patients were randomized to receive 12 capsules daily of Evening Primrose oil, providing 480 mg of GLA per day, or matched placebo capsules of liquid paraffin. Patients were evaluated at baseline and at 3, 6 and 12 months. Evening Primrose oil significantly (p<0.05) improved motor nerve conduction velocity, sensory nerve action potential, compound muscle action potential, tendon reflexes, and sensation in both the arm and leg compared to placebo (Keen et al, 1993).
In a randomized double-blind crossover study supplementation with Evening Primrose oil daily significantly altered fasting lipid profiles in 12 hyperlipidemic males. A significant reduction in mean serum triglycerides, total cholesterol, and LDL with a significant increase in mean HDL was reported following four months of Evening Primrose oil treatment (Guivernau et al, 1994).
In another study, Evening Primrose oil was not successful in changing serum cholesterol, HDL cholesterol or triglyceride levels in hyperlipidemic patients. (Viikari & Lehtonen, 1986). Supplementation with Evening Primrose oil did not affect serum lipoproteins or platelet function in hypertriglyceridemic patients (Boberg et al, 1986).
Irritable Bowel Syndrome
Fifty three percent of subjects showed improvements in irritable bowel symptoms with Evening Primrose oil. Subjects were given either eight 500 mg capsules of EPO daily (as Efamol®) or eight 500 mg capsules of olive oil as a placebo for 3 menstrual cycles in a placebo-controlled, double-blind, crossover study. Nineteen of 36 patients demonstrated an improvement on Efamol and none improved with placebo. Most subjects demonstrated improvement in the second month of treatment. The irritable bowel syndrome group had significantly lower levels of omega-6 fatty acids and also showed reduced docosapentanoic acid concentrations (Cotterell et al, 1990).
Fifty females with moderate to severe breast pain were given either Evening Primrose oil (OEP) or a topical non-steroidal anti-inflammatory (NSAID) gel in a one-year, randomized, and open comparative study to determine the relative safety, effectiveness, rapidity of response, cost-effectiveness, and acceptability of each regimen. While 64% of the 25 participants treated with OEP had a clinically significant response following 3 months of treatment, 92% of the 25 participants treated with topical NSAIDs had a clinically significant response. One patient taking OEP reported side effects, in contrast to none with topical NSAIDs. Acceptability rates for OEP and NSAIDs were 68% and 96%, respectively (Qureshi & Sultan, 2005).
More favorable results for Evening Primrose were obtained in a retrospective study covering seven years, in which 556 women with cyclical breast pain (mastalgia) were tracked. Most women were initially treated with Vitamin B-6 (pyridoxine HCL) 100 mg daily for a 3-month period. Those who did not respond were given 3 g of Evening Primrose Oil daily for 1 month followed by 2 g daily for an additional 2 months. Other participants were given the Evening Primrose oil regimen as first-line treatment; 58% of the Vitamin B6/EPO treatment group (71 patients) reported pain relief and 59% of the EPO first-line group (99 patients) reported relief. The author concluded that good responses can be obtained from products devoid of significant side effects, such as EPO and Vitamin B-6 as a first line treatment (McFayden, et al, 1992).
In an older review article, a clinician reported satisfactory treatment of mild mastalgia using three 500-mg doses of Evening Primrose oil twice daily for 1 month. Treatment that was considered successful after this time was continued 1 to 2 months longer. Patients were reported to have long-lasting effects even after the treatment period ended (Steinbrunn et al, 1997). The authors of a review on drug therapy in mastalgia recommended GLA 240 mg to 320 mg daily as a first-line therapy (Holland & Gateley, 1994).
Menopausal Hot Flushes
The effectiveness and safety of one versus two daily doses of a compound containing isoflavones (60 mg), Evening Primrose oil (440 mg), and vitamin E (10 mg) were assessed in an open, multi-center, randomized and group-comparative trial of 1,080 postmenopausal women with moderate to severe hot flushes. At 3 and 6 months, the two study dosages were equally effective in reducing hot flushes, with symptom reduction most significant for both groups in the first 3 months. The authors conclude that higher doses of the blend do not confer better results (Hidalgo et al, 2006).
Premenstrual Syndrome (PMS)
This review of four European studies concluded that Evening Primrose oil is effective in reducing the symptoms of PMS. One study involved 68 women who failed previous treatment for PMS. These women were treated with four Evening Primrose oil capsules daily starting in the luteal phase of the menstrual cycle and increasing to eight capsules daily. Sixty-one percent of these women experienced complete remission of symptoms, both physical and psychological. A second double-blind, placebo controlled study involved 42 patients given Evening Primrose oil for 3 months (dose not indicated). Participants in this study showed improvement in eight categories. The third study was double-blind, placebo controlled, and crossover in design (dose not indicated). Participants had 60% improvement of symptoms with Evening Primrose oil. The fourth study, which is unpublished, determined the value of treatment consisting of four daily capsules of Evening Primrose oil during the luteal phase of the cycle. With this low dose, patients had an improvement in five symptoms (Horrobin, 1983).
In one small study, however, Evening Primrose oil was shown to be ineffective in reducing PMS symptoms. Thirty-eight women took either 8 capsules of Evening Primrose oil or liquid paraffin as placebo on day one of their menstrual cycle through the end of their third cycle. At this time treatment was crossed-over for three more cycles. No differences were seen between the two treatment groups when rated on fluid retention, breast pain or swelling, and mood changes (Khoo et al, 1990).
A meta-analysis of nine controlled trials showed oral Evening Primrose oil provided significant (p<0.0001) improvement for patients with atopic eczema. All trials were randomized, double-blind, and placebo-controlled. At the first assessment time, Evening Primrose oil gave a significant (p<0.03) improvement from baseline on all three scores, while placebo gave significant improvement in none of the categories. At the last assessment time, Evening Primrose oil was still significant (p<0.0001) in all three categories and placebo showed significant (p=0.0001) improvement only in the clinical global score. The most striking improvement associated with GPO was in relieving itching. The degree of improvement correlated to the dose received, with 12 capsules per day giving the best results (Morse et al, 1989).
A recent, comprehensive follow-up of this meta-analysis concluded that Evening Primrose oil is safe and has a beneficial effect on itching, crusting, redness, and edema. The herb's benefits were shown to be apparent 4 to 8 weeks after the start of treatment. Increased steroid use reduces the magnitude of its beneficial effects, however. The investigators concluded that more research is needed to better comprehend the physiology and potential benefit of fatty acids such as Evening Primrose oil for atopic eczema (Morse & Clough, 2006).
In one older study involving 99 patients, 39 of which were children limited improvement in symptoms of atopic dermatitis with Evening Primrose oil use was demonstrated (Wright & Burton, 1982).
Indications & Usage
Evening Primrose oil is used for neurodermatitis, PMS, and as a dietary aid. EPO is also used to treat hyperactivity in children, high cholesterol levels, perimenopausal hot flashes, and cyclic mastalgia. Other common indications include hypertension, rheumatoid arthritis, thrombosis, autoimmune disease such as Multiple Sclerosis, and Raynaud's phenomenon. Capsules containing 500 mg of Evening Primrose oil have been approved for use in Germany, in the treatment of and to relieve the symptoms of atopic eczema.
Evening Primrose oil is contraindicated in patients with epilepsy.
Precautions & Adverse Reactions
Evening Primrose oil may cause mild gastrointestinal effects such as nausea, vomiting, diarrhea, flatulence, and bloating. There are case reports of seizures in schizophrenic patients that were being treated with Evening Primrose oil along with phenothiazine medications. Practitioners should be aware that Evening Primrose oil may lower the seizure threshold in patients with seizure disorders or in those being treated with drugs that lower the seizure threshold. In schizophrenic patients and those receiving epileptogenic drugs, Evening Primrose oil may have the potential to manifest temporal lobe epilepsy (Newall, 1996). Evening Primrose oil may potentiate temporal lobe epilepsy.
A study of 12 hyperlipidemic men taking 3 g Evening Primrose oil daily reported a significant mean 40% increase in bleeding time. A significant reduction in platelet aggregation response stimulated by low concentrations of ADP, adrenaline or collagen was also observed (Guivernau et al, 1993). A probable mechanism of action is inhibition of platelet thromboxane B2 production and increased vascular prostacyclin production leading to a reduction in platelet aggregation response (Guivernau et al, 1994).
It has been suggested that mothers of children with atopic eczema have an abnormal lipid content of their breast milk. Both studies suggest that supplementation of GLA via Evening Primrose oil can normalize the lipid content of breast milk and thus treat the child's atopic eczema. It seems that there is a greater proportion of linoleic acid and a smaller proportion of dihomo-GLA in total breast milk lipid content of these mothers compared to healthy controls (Melnik & Plewig, 1989; Wright, 1982).
Anticoagulants, Antiplatelet Agents, Low Molecular Weight Heparins, and Thrombolytic Agents
Concomitant use of Evening Primrose oil and these medications may increase the risk of bleeding. Clinical Management: Caution is advised if Evening Primrose oil and anticoagulants, antiplatelet agents, low molecular weight heparins, or thrombolytic agents are used concomitantly. Monitor for signs and symptoms of excessive bleeding.
Theoretically, Evening Primrose oil may reduce the effectiveness of anticonvulsants by lowering the seizure threshold. Clinical Management: Avoid concomitant use of Evening Primrose oil with anticonvulsants.
Evening Primrose oil may reduce the seizure threshold when taken with phenothiazines. Clinical Management: Avoid concomitant use of Evening Primrose oil with phenothiazines.
Mode of Administration
Evening Primrose oil is available in capsules for oral administration.
- Capsules–500 mg, 1300 mg.
- Most commercial products (capsules) are standardized for gamma linolenic acid content of 9%.
Treatment with Evening Primrose oil may require up to 3 months duration before positive results are attained for all indications listed below (Newall, 1996).
Adult–4 to 8 g daily in divided doses
Pediatric–2 to 4 g daily in divided doses
Mastalgia (breast pain)
3 to 4 g daily in divided doses
Evening Primrose oil is rinsed in nitrogen and stored in cooled tanks lined with polyethylene. Commercial products should be stored at room temperature in an area that is dry and not in direct sunlight.