Evening Primrose

Oenothera biennis

Family: Onagraceae Part used: Seeds (cold-pressed oil)

Key Compounds

• Gamma-linolenic acid (GLA)
• Linoleic acid
• Oleic acid
• Stearic acid
• Palmitic acid
• Tocopherols (vitamin E)
• Beta-sitosterol
• Campesterol
• Polyphenols

Traditional Use

• Atopic eczema — the application with most clinical trial support; 2003 Morse et al. Cochrane-style review of 26 RCTs; results varied but overall trend toward modest benefit for itching; GLA may normalise abnormal skin ceramide synthesis in atopic patients who have impaired delta-6-desaturase activity
• GLA supplementation — GLA (gamma-linolenic acid) is an omega-6 fatty acid found in few dietary sources; the metabolic pathway is: linoleic acid → (delta-6-desaturase enzyme) → GLA → dihomo-GLA (DGLA) → prostaglandin E1 (anti-inflammatory); many people have reduced delta-6-desaturase activity, particularly with ageing, diabetes, and alcohol use; EPO bypasses this conversion step by supplying GLA directly
• Premenstrual syndrome — traditional and clinical use for PMS-related breast tenderness (mastalgia) and mood symptoms; the GLA-prostaglandin E1 pathway may regulate prostaglandin balance in the premenstrual period; a 1981 Brush et al. study showed benefit for mastalgia specifically
• Rheumatoid arthritis — GLA at higher doses (2–3g/day) has shown anti-inflammatory effects in RA trials; the conversion of DGLA to 15-HETrE (anti-inflammatory) rather than arachidonic acid pathway prostaglandins is the proposed mechanism
• Diabetic neuropathy — several trials show benefit for peripheral neuropathy symptoms; GLA may normalise impaired essential fatty acid metabolism in diabetes; the 1993 Jamal and Carmichael RCT showed significant improvement in neuropathy scores
• Native American food and medicine — multiple Native American peoples of eastern North America used all parts of *Oenothera biennis*: seeds as food, roots cooked as vegetables, leaves as greens, and topically for wounds; the seed oil application is entirely modern

Evening primrose flowers open at dusk and are pollinated by moths.

The whole flower is designed for this. The pale yellow petals are visible to hawk moth eyes in low light. The sweet fragrance intensifies as the light fades. The flower opens rapidly — petals unfurling in minutes as the sun drops. The hawk moth arrives in the dusk, hovers, feeds, carries pollen to the next flower that opened twenty minutes ago. By morning, the flower has closed. In daylight, nothing happens.

The seed oil from this plant is one of the few plant sources of gamma-linolenic acid. The moth-targeted design and the unusual fatty acid are unrelated. Both are simply true.

Meet the plant

A biennial wildflower native to North America, now naturalised across Europe and beyond. Basal rosette in year one. Tall flowering stalk, 50–200 cm, in year two, bearing large pale-yellow four-petalled flowers. It grows in disturbed ground, roadsides, and open waste areas.

It arrived in Europe in approximately 1614 as a botanical curiosity. It naturalised within decades and became a European roadside weed. Three hundred years later, researchers began examining its seed oil.

The enzyme problem

The GLA story requires a brief metabolic explanation.

Omega-6 fatty acids include linoleic acid (LA) — common in plant oils, seed oils, and many foods. LA is converted in the body to GLA (gamma-linolenic acid) by an enzyme called delta-6-desaturase. GLA continues to DGLA (dihomo-gamma-linolenic acid), which then converts to prostaglandin E1 (PGE1) — an anti-inflammatory prostaglandin.

In healthy people, this pathway runs efficiently. Dietary linoleic acid is converted through GLA to PGE1 without supplementation. But delta-6-desaturase activity is impaired by: ageing, diabetes, alcohol consumption, viral infection, trans fat consumption, and nutritional deficiencies.

People with impaired delta-6-desaturase cannot efficiently make GLA from dietary LA. The anti-inflammatory prostaglandin pathway is effectively blocked at the first step.

Evening primrose oil supplies GLA directly. It bypasses the broken enzyme step and provides the intermediate the body needs. This is the pharmacological rationale for all GLA applications: supplementing the metabolic pathway downstream of the impaired enzyme.

The GLA content

Evening primrose seed oil contains approximately 8–10% GLA. This is high for a plant oil, though not the highest available:

• Borage oil (Borago officinalis): 20–25% GLA
• Blackcurrant seed oil: 15–18% GLA
• Evening primrose oil: 8–10% GLA

EPO has the largest clinical trial base. Borage oil provides more GLA per gram. Both are used for the same underlying rationale.

The rest of the oil is mostly linoleic acid (70–80%) with small amounts of oleic acid, stearic acid, palmitic acid, and tocopherols (vitamin E, which helps preserve the oil from oxidation).

What people actually do with it

Softgel capsules (standard preparation): 500–1000 mg per capsule; typical dose 1–3g daily. The oil is susceptible to oxidation — quality-controlled capsules with tocopherol antioxidant are preferable to bulk liquid.

For eczema: 2–4g daily, minimum 12 weeks to assess effect. The benefit, if present, takes weeks to months to appear — it is a fatty acid pathway intervention, not an acute treatment.

For PMS and mastalgia: Begin 2–3 weeks before anticipated symptoms; continue through the premenstrual period.

For diabetic neuropathy: Clinical trials used 6g/day — higher doses than typically sold in standard 500mg capsules.

Topical: EPO applied to skin is absorbed and contributes to skin barrier function. Used in moisturisers and eczema preparations.

Could you grow this yourself?

Easily. Evening primrose grows in poor, dry soil in full sun. It self-seeds prolifically and will colonise any disturbed ground. In Japan, it grows on roadsides and riverbanks throughout the country.

The seed oil extraction requires cold-pressing equipment. Growing the plant is simple; extracting the oil from the small seeds is not practical at home scale.

Evening primrose (月見草) in Japan

月見草 (tsukimisō — moon-viewing herb) is one of the more poetic plant names in Japanese, reflecting the evening bloom that was observed before the medicinal application was understood. The name connects the plant to the tradition of moon-viewing (お月見, o-tsukimi) — an autumn cultural practice in Japan. A plant that blooms at moonrise was naturally associated with the moon.

Evening primrose naturalised in Japan after European introduction and now grows as a common roadside plant throughout the country. Japanese consumers are familiar with evening primrose oil supplements, primarily for skin health (eczema support) and women’s health (PMS, breast tenderness). The GLA mechanism is understood in Japanese supplement marketing.

Things you’re probably wondering

Why does the flower open at night? Hawk moth pollination — large hovering moths that fly at dusk. The timing, scent, colour, and flower structure are all adaptations for this specific pollinator.

What is GLA? An omega-6 fatty acid that bypasses the delta-6-desaturase enzyme step. People with impaired enzyme activity (ageing, diabetes, alcohol) cannot efficiently make it from dietary linoleic acid; EPO supplies it directly.

Is the eczema evidence strong? Moderate. A review of 26 trials showed variable results; overall trend toward modest benefit, particularly for itch. More convincing for patients with demonstrated abnormal essential fatty acid metabolism.

How does it compare to borage oil? Borage oil has 20–25% GLA versus EPO’s 8–10% — more GLA per gram. EPO has a larger clinical trial base. Both are used for GLA supplementation.

Botanical details

The full fatty acid profile (EPO)

See Also

• Borage — higher GLA content (20–25%); same supplementation rationale
• Chamomile — topical anti-inflammatory for eczema; complementary application
• Calendula — topical skin-healing herb; often combined with EPO in eczema care

References

• Morse, P.F. & Horrobin, D.F. et al. (1989). Meta-analysis of placebo-controlled studies of evening primrose oil in atopic eczema. British Journal of Dermatology, 121(1), 75–90.
• Jamal, G.A. & Carmichael, H. (1990). The effect of gamma-linolenic acid on human diabetic peripheral neuropathy. Diabetic Medicine, 7(4), 319–323.
• Horrobin, D.F. (1993). Fatty acid metabolism in health and disease. American Journal of Clinical Nutrition, 57(5 Suppl), 732S–737S.
• Bamford, J.T. et al. (2013). Oral evening primrose oil and borage oil for eczema. Cochrane Database of Systematic Reviews, Issue 4.