Evening Primrose Oil
Also known as: EPO, Oenothera biennis seed oil, primrose oil, GLA oil
Evening primrose oil is pressed from the seeds of Oenothera biennis and is valued for its gamma-linolenic acid (GLA), an omega-6 fatty acid that usually makes up 8-10% of the oil, with linoleic acid as the bulk. It has been studied mainly in women's health contexts such as cyclical breast discomfort and menopausal hot flashes, and in skin conditions. Formulators dose it as milligrams of whole oil and commonly place it in women's hormone, skin, and PMS-positioned softgel products.
Research summary
GLA is converted to dihomo-gamma-linolenic acid, a precursor of series-1 prostaglandins, shifting the balance of eicosanoid production.
Dosage
Daily amounts, of compound.
| Lowest studied | Typical range | Highest studied | Upper limit |
|---|---|---|---|
| 500 mg | 500–1,300 mg | — | — |
Dosed as mg whole oil. Trials pooled in the mastalgia and menopause meta-analyses generally ran for several weeks to months; the pooled analyses report modest or inconsistent symptom effects and no excess of adverse events versus placebo. The highest dose used across those trials was not extractable from the abstracts and is left null. Usually taken in divided doses with meals; effects, where seen, take weeks.
Standardization: Declare GLA content (commonly 8-10% of oil, e.g. 40-50 mg GLA per 500 mg)
Source material: cold-pressed evening primrose seed
As supplied: About 80-100 mg GLA per 1,000 mg oil
Format suitability
- Capsule
- Powder
- Tablet
- Softgel
- Gummy
- Liquid
Oil-based; softgel or liquid only. 500 mg and 1,000 mg softgels are standard; 1,300 mg softgels are used for once-daily products.
Formulation notes
Historically cautioned with phenothiazines and in seizure disorders; note as a formulation-level caution. Often paired with vitamin E, which also protects the oil from oxidation.
- Notable drug interactions
Sources
- A Systematic Review and Meta-Analysis of the Efficacy of Evening Primrose Oil for Mastalgia Treatment. (Ahmad Adni 2021)PubMed
- Evening Primrose Oil for Menopause Hot Flashes: Systematic Review and Meta-Analysis. (Thevi 2024)PubMed
- Oral evening primrose oil and borage oil for eczema. (Bamford 2013)PubMed
Related ingredients
Flaxseed Oil
Fatty acidFlaxseed oil is cold-pressed from flax (Linum usitatissimum) seeds and is the richest common plant source of alpha-linolenic acid (ALA), a short-chain omega-3 that typically makes up 50-60% of the oil.
Typical: 1,000–3,000 mg
Sea Buckthorn Oil
BotanicalSea buckthorn oil is pressed or CO2-extracted from the berries and seeds of Hippophae rhamnoides, a hardy shrub native to Europe and Asia.
Typical: 500–2,000 mg
Borage Oil
Fatty acidBorage oil is pressed from the seeds of Borago officinalis and is the most concentrated common plant source of gamma-linolenic acid, typically around 20% GLA, roughly twice the level in evening primrose oil.
Typical: 500–1,000 mg
Fish Oil (EPA/DHA Concentrate)
Fatty acidFish oil concentrate is a refined marine oil enriched in the long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
Typical: 500–2,000 mg
Vitamin C (Ascorbic Acid)
VitaminAscorbic acid is the reference form of vitamin C and the most common form in supplements; NIH ODS notes its bioavailability equals that of vitamin C naturally present in food.
Typical: 250–1,000 mg