Evening Primrose Oil (Oenothera biennis)
Evening primrose oil (Oenothera biennis seed oil) is a botanical oil whose distinguishing fraction is gamma-linolenic acid (GLA, 18:3 n-6) at 8–10% of total fatty acids. Sold in the UK as a food supplement at 500–3000 mg/day. NO UK food-supplement health claims are authorised for EPO or GLA. Two former UK- licensed EPO medicinal products (Efamast for cyclical mastalgia, Epogam for atopic eczema) were withdrawn by the MHRA in 2002 after efficacy reviews; the substance remained lawful as a food supplement but the medicinal-claim history means UK supplement copy must not invoke eczema or mastalgia treatment language. The Cochrane review on dietary supplements for eczema (Bamford 2013) found no improvement in atopic eczema. Anticoagulant and antipsychotic-class interactions are documented. Pregnancy third trimester: avoid.
Camden Medicals editorial · Last reviewed 4 May 2026 · Next review November 2026
- Cross-checked against
- NHS
- NICE
- BNF
- EFSA
- FSA
Camden's editorial team independently graded each health claim below on the strength of the published evidence — see the grade beside every condition.
- Class
- Fatty acid
- Top use evidence
- Limited
On this page
What it is
Evening primrose (Oenothera biennis) is a herbaceous biennial plant native to North America, now naturalised across Europe including the UK. The yellow flowers open in the evening, which is the source of the common name. Commercial evening primrose oil is cold-pressed from the plant''s seeds, then refined and deodorised before encapsulation. The oil is yellow, mild-tasting, and oxidation-prone — well-formulated commercial product incorporates an antioxidant carrier (typically vitamin E as mixed tocopherols or D-alpha tocopherol).
The compositional point of interest is the fatty-acid profile, specifically the gamma-linolenic acid (GLA, 18:3 n-6) fraction. GLA is an n-6 polyunsaturated fatty acid that the body normally synthesises from dietary linoleic acid via the delta-6-desaturase enzyme. The supplement rationale historically rested on the hypothesis that some individuals — older adults, people with diabetes, people with eczema, or others under metabolic stress — may have reduced delta-6-desaturase activity and benefit from pre-formed GLA in the diet. Borage seed oil and blackcurrant seed oil also contain GLA at higher percentages (borage 17–25%, blackcurrant 15–20%), but borage oil carries pyrrolizidine- alkaloid contamination concerns in some commercial preparations and is not a clean substitute for EPO.
UK regulatory history is load-bearing for editorial framing. Two licensed UK medicines incorporating EPO — Efamast (for cyclical mastalgia) and Epogam (for atopic eczema) — were withdrawn by the Medicines and Healthcare products Regulatory Agency (MHRA) in 2002 after evidence reviews concluded the efficacy data did not support continued licensing for those indications. The substance itself remained lawful as a food supplement; the withdrawal applied to the medicinal-claim licences, not to the underlying ingredient. This distinction is editorially load-bearing — UK supplement marketing for EPO must not reach back to those withdrawn indications, and the Cochrane systematic review on dietary supplements for atopic eczema (Bamford et al, 2013) explicitly concluded EPO does not improve eczema. There are NO EFSA-authorised UK food-supplement health claims under Regulation 1924/2006 (retained) for EPO or for gamma-linolenic acid as such.
At a glance
- A botanical seed oil from the Oenothera biennis plant. The chemistry of interest is the gamma-linolenic acid fraction (GLA, 18:3 n-6), typically 8–10% of total fatty acids, so a 1000 mg softgel delivers roughly 80–100 mg GLA. Bulk EPO milligrams are less informative than the GLA milligrams on the label.
- NO UK-authorised food-supplement health claims attach to evening primrose oil or to gamma-linolenic acid under Regulation 1924/2006 (retained). UK supplement copy must therefore stay descriptive.
- Important UK regulatory history: Efamast (for cyclical mastalgia) and Epogam (for atopic eczema) were licensed UK medicines containing EPO that were withdrawn by the MHRA in 2002 after evidence reviews concluded efficacy was insufficient. The substance remained lawful as a food supplement; the withdrawal applied to medicinal claims. UK supplement marketing must NOT invoke eczema treatment, mastalgia treatment, or any other former medicinal-indication claim.
- Cochrane review on dietary supplements for atopic eczema (Bamford et al, 2013) concluded EPO and borage oil do NOT improve atopic eczema in children or adults. NHS and NICE eczema guidance do not list EPO among recommended interventions. Eczema-positioning marketing on EPO is editorially unsafe and regulatorily prohibited.
- Anticoagulant interaction — GLA is metabolised to dihomo-gamma-linolenic acid (DGLA) and onward to series-1 prostaglandins, with a theoretical antiplatelet effect at supplement doses. Disclose use to your prescriber if you take warfarin, DOACs, aspirin, clopidogrel, or NSAIDs. Phenothiazine antipsychotic interaction (lowered seizure threshold) is a historical caution.
- Pregnancy and breastfeeding: avoid in the third trimester (theoretical cervical-priming / prostaglandin effect on labour). Earlier pregnancy and lactation: insufficient safety data, generally avoid pending specialist advice. Borage oil is NOT an interchangeable substitute — it carries pyrrolizidine-alkaloid contamination concerns of its own.
What people use it for
Adults exploring nutritional support for skin comfort or premenstrual symptom management
Evening primrose oil is one of several botanical-oil options some adults try for skin and women-cycle comfort, despite the limited clinical-outcome evidence base. UK supplement marketing must not invoke eczema treatment, mastalgia treatment, or PMS treatment claim language. Honest framing positions EPO as a GLA-bearing dietary oil with a long traditional-use history rather than as a treatment for any defined condition. [1]
Some evidenceLimitedAdults whose vitamin-E and B6 needs are not fully met by diet
Complex EPO formulas that include vitamin E (sunflower-derived D-alpha tocopherol) and vitamin B6 (pyridoxine hydrochloride) at meaningful doses can claim — for those nutrient components only — authorised wording around protection of cells from oxidative stress (vitamin E) and contribution to normal psychological function and reduction of tiredness and fatigue (B6). The EPO and GLA components themselves carry no authorised claim wording. [2]
Some evidenceLimited
How it works
Gamma-linolenic acid is metabolised to dihomo-gamma-linolenic acid (DGLA) and then to a mix of series-1 prostaglandins (PGE1, mechanistically anti-inflammatory and antiplatelet) and series-2 prostaglandins via further conversion to arachidonic acid. The supplement rationale rested on the idea that pre-formed GLA bypasses a potentially rate-limiting delta-6- desaturase step and so favours the DGLA / PGE1 axis over the arachidonic-acid / pro-inflammatory series-2 prostaglandins. The mechanistic story is plausible but the translation to consistent human clinical-outcome benefit has been the long- standing weak link — for atopic eczema the Cochrane review found no benefit; for cyclical mastalgia the MHRA evidence review found insufficient efficacy data; for premenstrual syndrome the evidence base remains modest. The vitamin-E component of well-formulated commercial EPO products serves primarily as an antioxidant carrier to protect the oil from oxidation rather than as a supplemental nutrient at material dose.
Common myths
Myth""Evening primrose oil is a natural eczema treatment.""
RealityIt isn't — and saying so is regulatorily prohibited in UK supplement copy. The Cochrane systematic review (Bamford 2013) concluded EPO does not improve atopic eczema in children or adults. The UK MHRA withdrew Epogam (a licensed EPO medicine for eczema) in 2002 on efficacy grounds. NHS and NICE eczema guidance do not recommend it. People with diagnosed eczema should follow their dermatology / GP-guided care pathway. [3,1]
Myth""EPO helps cyclical breast pain (mastalgia).""
RealityThe UK regulator's formal determination on this question was the 2002 withdrawal of Efamast — a licensed EPO medicine specifically indicated for cyclical mastalgia — after the evidence review concluded the data did not support continued licensing. RCOG and NICE breast-pain guidance do not list EPO among recommended interventions. UK supplement marketing cannot invoke mastalgia treatment claim language.
Myth""Higher milligrams of EPO is better.""
RealityWhat matters is the gamma-linolenic acid fraction, not bulk EPO milligrams. Typical commercial EPO is 8–10% GLA, so a 1000 mg softgel delivers ~80–100 mg GLA. The label should state the GLA content explicitly. A "high-strength 3000 mg EPO" without a GLA disclosure is a marketing-strength claim, not a chemistry-strength claim.
Myth""EPO and borage oil are interchangeable.""
RealityBoth are GLA sources but borage oil contains 17–25% GLA versus EPO's 8–10%. More importantly, borage seed oil from some commercial preparations carries pyrrolizidine-alkaloid contamination concerns; the purified UPA-free borage oil is the supplement-grade form. EPO does not have this contamination concern. The two are different supplement-grade ingredients with different quality-marker considerations.
Myth""It's safe in pregnancy because it's natural.""
RealityNaturalness-as-safety arguments are particularly weak in pregnancy. Third-trimester EPO is sometimes promoted for cervical priming or labour induction; the evidence base is thin and the precautionary stance is to avoid in the third trimester. Earlier pregnancy and lactation: insufficient safety data, avoid pending specialist advice. [4]
🔬 Camden’s evidence review
The research Camden reviewed, graded on its strength. This is our own appraisal — it sits beneath the official guidance above, never above it.
Atopic eczema
StrongEvidencestrongThe Cochrane systematic review on dietary supplements for atopic eczema (Bamford et al, 2013) included multiple randomised trials of evening primrose oil and borage oil and concluded these supplements do NOT improve eczema severity in adults or children. NHS atopic-eczema treatment guidance does not list EPO among recommended interventions. NICE does not recommend it. The 2002 UK MHRA withdrawal of Epogam (a licensed EPO medicine for atopic eczema) on efficacy grounds is the authoritative UK regulatory determination. Marketing in this category is editorially prohibited and regulatorily indefensible. [3,1,5]
Cyclical mastalgia (cyclical breast pain)
InsufficientEvidenceinsufficientEfamast was a licensed UK medicine containing EPO indicated for cyclical mastalgia. The MHRA withdrew the product licence in 2002 after evidence review concluded efficacy data was insufficient. RCOG and NICE breast-pain guidance do not list EPO among recommended interventions for cyclical mastalgia. UK supplement marketing in this category is editorially unsafe. [6,2]
Premenstrual syndrome (PMS) symptom management
InsufficientEvidenceinsufficientEPO is sometimes promoted for premenstrual symptoms; the clinical-outcome evidence is older, mixed, and modest. RCOG premenstrual syndrome guidance does not list EPO among recommended interventions. UK supplement marketing cannot invoke PMS treatment claim wording. [6]
Diabetic neuropathy
InsufficientEvidenceinsufficientOlder trials in the 1990s explored GLA at relatively high doses (480–600 mg GLA / day) for diabetic peripheral neuropathy with mixed results. NICE diabetic-neuropathy guidance (NG28 diabetes-in-adults) does not list EPO or GLA among recommended interventions. UK supplement marketing in this category is editorially unsafe. [7]
Rheumatoid arthritis symptom management
InsufficientEvidenceinsufficientLimited older trials at high GLA doses (1.4–2.8 g/day) suggested modest reduction in inflammatory-arthritis symptoms. NICE rheumatoid-arthritis guidance (NG100) does not list EPO. UK supplement marketing on this evidence is editorially unsafe; people with diagnosed rheumatoid arthritis must follow NICE-guided care. [8]
Safety
Pregnancy and breastfeeding
Avoid in the third trimester (theoretical cervical-priming and prostaglandin effect on labour onset). Earlier pregnancy: insufficient safety data; conservative avoidance pending specialist advice. The historical practice of late-pregnancy EPO use for labour induction is not evidence-supported and is not recommended on safety grounds.
Insufficient safety data on lactation exposure. Avoid pending specialist advice.
Talk to your GP, midwife, or pharmacist before starting any supplement during pregnancy or breastfeeding.
Contraindications
- Documented seizure disorder treated with phenothiazine antipsychotics (chlorpromazine, prochlorperazine, fluphenazine) — historical case reports of lowered seizure threshold; conservative avoidance.
- Use within 14 days of major surgery — antiplatelet potential of the GLA / DGLA / PGE1 pathway warrants peri-operative pause.
- Third-trimester pregnancy (theoretical cervical-priming / prostaglandin effect on labour).
Drug interactions
- Anticoagulants (warfarin, DOACs) and antiplatelets (aspirin, clopidogrel, ticagrelor, NSAIDs): GLA → DGLA → PGE1 pathway has antiplatelet activity at supplement doses. Disclose use to your anticoagulation team and avoid in the peri-operative window.
- Phenothiazine antipsychotics (chlorpromazine, prochlorperazine, fluphenazine, perphenazine): historical case reports of lowered seizure threshold with concurrent EPO use. Conservative avoidance.
- Anticonvulsants (sodium valproate, carbamazepine, phenytoin, lamotrigine): potential interaction not well characterised but the seizure-threshold concern with phenothiazines extends a conservative caution to other CNS-active drugs in seizure disorders. Discuss with neurology.
- NSAIDs (ibuprofen, naproxen, diclofenac): combined antiplatelet effect; not a contraindication but disclose at GP review.
This is not an exhaustive list. Always tell your prescriber and pharmacist about every supplement you take.
Common side effects
- Mild gastrointestinal upset (nausea, soft stool, abdominal discomfort) at higher per-day doses — typically resolves with dose reduction or food co-intake.
- Headache, particularly at the start of higher-dose regimens.
Rare side effects
- Allergic reaction (rash, urticaria) in individuals sensitive to Onagraceae-family plants.
- Increased bleeding tendency at higher per-day doses, especially when combined with antiplatelet medication.
- Lowered seizure threshold reported historically with concurrent phenothiazine antipsychotic use — uncertain mechanism; conservative avoidance.
How to take it
- Timing
- Take with food (the oil is fat-soluble; food co-intake supports absorption and reduces gastrointestinal upset). Splitting the dose across two meals if taking multiple softgels is reasonable. No specific time-of-day recommendation.
How to spot quality
Look for
- GLA percentage AND GLA milligrams declared on the label and CoA — not just bulk EPO milligrams. Typical cold-pressed EPO is 8–10% GLA; below 8% suggests low-quality material or oxidative degradation; above 12% is unusual for EPO and may signal a different botanical source (borage / blackcurrant).
- Cold-pressed and refined extraction route disclosed on the CoA. Solvent-extracted EPO is less common in supplement-grade material but should be disclosed when used (residual hexane testing required).
- Antioxidant carrier disclosed — vitamin E as mixed tocopherols or D-alpha tocopherol is the standard for protecting the oil from oxidation. A peroxide-value (PV) figure on the CoA is the gold-standard quality marker; PV below 5 mEq/kg is the typical specification for fresh oil.
- Capsule shell composition disclosed — gelatin softgels are not vegan; modified-starch + carrageenan softgels (the vegan softgel path) are vegan. Camden labels should make vegan / non-vegan status explicit per `format.dietary` declaration.
- Country of cultivation declared (UK / European / North American is typical; provenance affects pesticide-residue profile).
- Pesticide-residue and heavy-metal panel on the CoA — Oenothera biennis is a wild-and-cultivated plant; provenance affects contamination risk.
Red flags
- Generic "Evening Primrose Oil 1000 mg" without GLA percentage or GLA milligram declaration on the label.
- Atopic eczema, mastalgia, premenstrual syndrome, or "natural skin treatment" marketing language not authorised under UK Regulation 1924/2006 (none exist for EPO; the 2002 MHRA Epogam / Efamast withdrawals are the authoritative UK position).
- Per-day dose recommendations above 3000 mg EPO without explicit reference to the published trial range.
- Absence of antioxidant carrier (vitamin E or equivalent) or absence of peroxide-value figure on the CoA — fresh EPO must be antioxidant-protected.
- Substitution of borage seed oil for evening primrose oil under an "EPO" label — different botanical, different GLA content, different contamination considerations.
Commonly combined with
Other ingredients that share a biological pathway, cofactor relationship, or evidence-backed protocol with this one. Mechanisms below cite primary physiology — not folk pairing. Doses are literature ranges, not recommendations. Talk to your pharmacist or GP before changing your stack, especially if you take prescription medication.
Fish Oil (Long-Chain Omega-3 EPA / DHA, Marine Source)
Limited evidenceOmega-fatty-acid cluster — EPO GLA (n-6) + fish oil EPA / DHA (n-3). Mechanism complementary across n-6 / n-3 axes.
EPO GLA → DGLA → series-1 prostaglandins (anti-inflammatory) at n-6 axis; fish oil EPA → series-3 prostaglandins (anti-inflammatory) at n-3 axis. Different prostaglandin pathways.
Evidence: Both have UK regulatory tier; fish oil has authorised heart / brain / vision claims.
Doses studied: 1000-2000 mg EPO + 1000-2000 mg fish oil daily.
Flaxseed (Linum usitatissimum) — whole seed, oil, and lignans
Limited evidencePlant-omega cluster — EPO GLA + flaxseed ALA overlap on essential-fatty-acid framing.
EPO GLA n-6; flaxseed ALA n-3. Different essential fatty acids. Common co-formulation in UK plant-omega blends.
Evidence: Camden flaxseed + EPO entries cover cluster.
Doses studied: 1000-2000 mg EPO + 1000-2000 mg flaxseed oil daily.
Vitamin E (alpha-tocopherol)
Limited evidencePolyunsaturated-fatty-acid antioxidant pairing — vitamin E protects PUFA from peroxidation.
α-tocopherol scavenges lipid peroxyl radicals in PUFA-rich membranes. Co-formulation supports oxidative stability of EPO GLA + storage. UK Article 13.1 vitamin E cell-protection claim authorised.
Evidence: UK Article 13.1 vitamin E claim authorised. [2]
Doses studied: 1000-2000 mg EPO + 12 mg vitamin E daily.