Evening Primrose Oil
Evidence Fact Sheet
GLA
Evening primrose oil (Oenothera biennis seed oil) is a dietary source of gamma-linolenic acid (GLA), an n-6 fatty acid studied for skin, menopause and inflammatory-response support. Pooled meta-analyses for eczema, hot flashes and mastalgia have largely been null; inflammatory evidence is heterogeneous. A DSHEA-legal supplement with no authorized health claims.
Also known as: Evening Primrose Oil · EPO · Oenothera biennis seed oil · GLA oil · Gamma-linolenic acid (GLA) source oil
Overview
Evening primrose oil (EPO) is the seed oil of Oenothera biennis, valued as a dietary source of preformed gamma-linolenic acid (GLA), which bypasses the rate-limiting delta-6-desaturase step of the n-6 fatty-acid pathway; GLA is elongated to dihomo-gamma-linolenic acid (DGLA), a precursor for series-1 prostaglandins studied in inflammatory signaling. The oil is also rich in linoleic acid plus minor tocopherols, phytosterols and phenolics. Typical research and marketed doses fall in the 1-4 g/day range (delivering roughly 80-320 mg GLA at 7-10% GLA content) over 4-12 weeks. It is generally well tolerated, with caution flags for seizure threshold and pre-surgical bleeding/antiplatelet interaction. Regulatory status: a DSHEA-legal dietary supplement in the US (structure/function claims only), a permitted EU food-supplement ingredient with zero EFSA-authorized health claims, a permitted ANVISA food-supplement ingredient in Brazil, and a national-standard edible oil (conventional food) in China. Educational information, not medical advice or a dosing recommendation.
Mechanism of Action
Supplies preformed gamma-linolenic acid (GLA), bypassing the rate-limiting delta-6-desaturase step in the n-6 fatty-acid pathway (research-context mechanism) · GLA is elongated to dihomo-gamma-linolenic acid (DGLA), a precursor for series-1 prostaglandins (e.g. PGE1) studied for their role in inflammatory signaling · Seed oil is also rich in linoleic acid (~70%) plus minor phenolics, tocopherols and phytosterols characterized in compositional reviews
Body systems: Skin & Connective Tissue · Immune System · Reproductive
Evidence-Based Benefits
Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Evening Primrose Oil is not characterized as a treatment for any disease.
Eczema / Atopic Dermatitis
Null / no benefit Meta-analysis supported- -2.22 (95% CI -10.48 to 6.04)mean diff · 0-100 VAS
- 27 studies1596 participants
- 19 studiesassessed EPO
In the Cochrane systematic review and meta-analysis, oral evening primrose oil did not significantly improve global eczema symptoms versus placebo; the pooled mean difference on a 0-100 visual analogue scale crossed zero. The authors concluded EPO lacks effect on eczema, with improvement similar to placebo. This is a prominent honest negative.
Reported effect: mean difference of -2.22 (95% CI -10.48 to 6.04) on a 0-100 visual analogue scale; 27 studies (1596 participants), 19 assessed EPO
“EPO failed to significantly increase improvement in global eczema symptoms as reported by participants, with a mean difference of -2.22 (95% CI -10.48 to 6.04) on a 0-100 visual analogue scale. Oral borage oil and evening primrose oil lack effect on eczema; improvement was similar to respective placebos used in trials.”
Source: PMID 23633319 · Bamford 2013 · Cochrane Database Syst Rev
Menopausal Hot Flashes
Null / no benefit Meta-analysis supported- -2.13 per dayhot flashes · not significant
- 6 RCTs450 women
- -0.19intensity · not significant
In this systematic review and meta-analysis of 6 RCTs (450 women), the EPO group showed a mean decrease of 2.13 hot flashes per day versus control, but the difference was not statistically significant; the reduction in intensity was also non-significant. A reduction in hot-flash duration was reported as significant, leaving the overall picture mixed and the headline frequency outcome null.
Reported effect: mean decrease of 2.13 hot flashes per day vs control (not statistically significant); 0.19 reduction in intensity (not significant); 6 RCTs, 450 women
“the women in the EPO group experienced a mean decrease of 2.13 in the number of hot flashes per day compared to the control group. Still, it was not statistically significant. ... The EPO group experienced a 0.19 reduction in hot flash intensity, but this reduction was not statistically significant.”
Source: PMID 41883983 · Larki 2025 · J Caring Sci
Mastalgia / Cyclical Breast Pain
Null / no benefit Meta-analysis supported- 13 trials1752 patients
- no differencepain relief vs placebo
This systematic review and meta-analysis of 13 trials (1,752 randomized patients) found EPO had similar efficacy for pain control compared with placebo, topical NSAIDs, danazol or vitamin E. The number of patients achieving pain relief was no different from placebo or other treatments, though EPO was characterized as safe. An honest null result.
Reported effect: no difference in pain relief vs placebo, topical NSAIDs, danazol or vitamin E; 13 trials, 1,752 randomized patients
“EPO is a safe medication with similar efficacy for pain control in women with mastalgia compared to a placebo, topical NSAIDS, danazol, or vitamin E. ... The number of patients who achieved pain relief was no different compared to the placebo or other treatments.”
Source: PMID 34200727 · Ahmad Adni 2021 · Int J Environ Res Public Health
Inflammatory Disorders
Emerging / indexedA systematic review noted some evidence for potential benefits of EPO in inflammatory disorders, but the contemporary literature was found to be highly heterogeneous and unable to support strong recommendations. The abstract describes a direction without reporting a pooled effect size, so no number is extracted (verified=false for the numeric claim).
Effect size: this study reports the direction of the finding but does not state a specific numeric effect size, so none is given here rather than estimated.
“Some evidence regarding the potential benefits of EPO in inflammatory disorders were reported however caution is due to the limitations of the current survey. ... contemporary literature is highly heterogeneous and fails to provide strong recommendations regarding the efficacy of EPO on inflammatory disorders.”
Source: PMID 38360611 · Sharifi 2024 · BMC Complement Med Ther
Dosage (research context · not a recommendation)
1-4 g/day of evening primrose oil (delivering roughly 80-320 mg GLA at 7-10% GLA content) over 4-12 weeks in clinical trials; 1-3 g/day is the common marketed range. Educational reference, not a dosing recommendation.
Regulatory Status · 4 Markets
- US · FDA
- DSHEA-legal dietary supplement ingredient (women's-health / skin category); marketed with structure/function claims only — no FDA-authorized health claim for EPO
- EU · EFSA
- Permitted food-supplement ingredient in the EU; ZERO EFSA-authorized health claims for evening primrose oil / GLA (only neutral compositional description permitted)
- CN · China
- Conventional food in China — evening primrose oil is a national-standard edible oil (GB/T 46116-2025); it is not listed in the SAMR health-food raw-material catalogue.
- BR · ANVISA
- Permitted food-supplement ingredient in Brazil under the RDC 243/2018 / IN 28/2018 framework; no standalone authorized functional claim
Safety
Generally well tolerated with a long history of dietary use; the most common adverse effects in trials are occasional headache and mild gastrointestinal upset. Caution flags: case reports suggest EPO may lower the seizure threshold, so individuals with epilepsy should use it cautiously; GLA-rich oils may add to bleeding/antiplatelet effects, so discontinue before surgery and use care with anticoagulants. Pregnancy/obstetric use (e.g. for cervical ripening) is a clinical, not supplement, context and not supported. Educational information, not medical advice.
Related
Goals: menopause-support · skin-beauty
Lifestyles: menopause
References
PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.
- PMID 23633319 · Bamford 2013 · Cochrane Database Syst Rev — Eczema / Atopic Dermatitis
- PMID 41883983 · Larki 2025 · J Caring Sci — Menopausal Hot Flashes
- PMID 34200727 · Ahmad Adni 2021 · Int J Environ Res Public Health — Mastalgia / Cyclical Breast Pain
- PMID 38360611 · Sharifi 2024 · BMC Complement Med Ther — Inflammatory Disorders
Frequently Asked Questions
1. Does evening primrose oil help eczema?
The strongest evidence does not support it. A Cochrane meta-analysis (Bamford 2013, 27 studies / 1596 participants, 19 assessing EPO) found oral evening primrose oil did not significantly improve global eczema symptoms versus placebo, with a mean difference of -2.22 (95% CI -10.48 to 6.04) on a 0-100 scale. This is reported here as a research finding, not treatment guidance.
2. Can evening primrose oil reduce menopausal hot flashes?
The evidence is mixed and largely null on frequency. A 2025 systematic review and meta-analysis of 6 RCTs (450 women) found the EPO group had a mean decrease of 2.13 hot flashes per day versus control, but this was not statistically significant, and the 0.19 reduction in intensity was also non-significant. A reduction in duration was reported as significant, leaving an inconsistent overall picture.
3. Is evening primrose oil effective for cyclical breast pain (mastalgia)?
Pooled data say no clear benefit. A meta-analysis of 13 trials (1,752 randomized patients) found EPO had similar efficacy for pain control compared with placebo, topical NSAIDs, danazol or vitamin E, with the number of patients achieving pain relief no different from placebo. EPO was, however, characterized as safe.
4. What is gamma-linolenic acid (GLA) and how much is in evening primrose oil?
GLA is an n-6 fatty acid that evening primrose oil supplies in preformed dietary form, bypassing the rate-limiting delta-6-desaturase step; it is then elongated to DGLA, a precursor for series-1 prostaglandins studied in inflammatory signaling. EPO is roughly 7-10% GLA, so the common research and marketed dose range of 1-4 g/day delivers roughly 80-320 mg GLA. This is educational reference, not a dosing recommendation.
Last evidence review: 2026-06-13