A seed oil containing roughly 8–10% gamma-linolenic acid, an omega-6 fatty acid. Borage and blackcurrant seed oils are alternative GLA sources with different profiles.
Evening primrose oil has been trialled extensively for eczema, breast pain and menopausal symptoms, and the pattern is consistently disappointing. A Cochrane review of eczema trials found no meaningful benefit; UK regulators withdrew the licences of two evening primrose oil eczema medicines in 2002 because the evidence did not support them. It remains one of the best-selling supplements in the category.
Sold as
Softgel capsule, Liquid oil, Topical preparation
Standardised to
Usually stated as GLA content per capsule, commonly 40–100 mg — a product without this marker may not resemble what was studied.
Also known as
EPO, Gamma-linolenic acid, GLA, Oenothera oil
Regulation: UK medicines licences for evening primrose oil in atopic eczema were withdrawn in 2002 after review found the evidence of efficacy insufficient. It continues to be sold as a supplement.
What the research used
The amounts, forms and durations published trials of Evening primrose oil actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Pooled trials at these doses found no meaningful improvement in eczema severity, which is why the medicine licences were withdrawn. The doses are recorded here because they are what was tested, not because they worked.
Studied for Cyclical breast pain and menopausal symptoms
1–4 g
Limited
Softgel capsules, divided doses · 6 weeks to 6 months
Trials are small and mostly negative or equivocal; where positive results appear they are frequently in combination with vitamin E or other agents.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🍽️With food
Limited
A fat-soluble oil taken with meals for absorption and to reduce nausea. Sensible pharmacology, but not compared in a trial.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Limited
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Pooled trials in atopic eczema found no meaningful improvement in symptoms compared with placebo, and regulators withdrew medicine licences on that basis. Marketing for skin continues regardless.
Limited evidence. Early human work, or mostly lab and animal research.
Evidence is limited for evening primrose oil and hot flushes. Trials are small and results inconsistent, with the better-controlled ones showing no difference from placebo.
Not enough evidence. Not enough human research to say anything useful yet.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Interaction
Seizure threshold with phenothiazines and anaesthesia
Interacts withPhenothiazines, anaesthetic agents
Seizures have been reported in people taking evening primrose oil with phenothiazine antipsychotics, and anaesthetists advise stopping it two weeks before surgery because of seizure and bleeding concerns.
Worth knowing
Borage oil is not an equivalent substitute
Borage seed oil is often sold as a higher-GLA alternative, but borage contains pyrrolizidine alkaloids, which cause hepatic veno-occlusive disease. Only certified alkaloid-free borage oil avoids that risk, and the same alkaloid family is why comfrey and coltsfoot are not taken internally.
Interaction
Bleeding risk
Interacts withWarfarin, direct oral anticoagulants, aspirin
Gamma-linolenic acid affects platelet aggregation, so caution applies with warfarin, direct oral anticoagulants and aspirin.
Worth knowing
Pregnancy and labour
Evening primrose oil is used by some to prepare for labour; observational data have raised questions about prolonged labour and complications, and it is not established as safe in pregnancy.
Worth knowing
Oxidation and digestive upset
Polyunsaturated seed oils oxidise readily; rancid capsules taste unpleasant and are best discarded. Nausea, loose stools and headache are the commonly reported effects.