Short answer: the evidence that evening primrose oil (EPO) meaningfully relieves hot flashes, night sweats, or other menopause symptoms is insufficient. A handful of small, mostly low-quality trials have produced mixed results, and no major medical body currently recommends it for menopausal hot flashes. It is usually well tolerated, but "natural" does not mean risk-free — it can interact with a few common medications. Here is what the science actually shows, claim by claim.

What evening primrose oil is

Evening primrose oil is pressed from the seeds of the Oenothera biennis plant. It is rich in omega-6 fatty acids, especially gamma-linolenic acid (GLA), which is the ingredient marketers usually point to. It is sold as a supplement for a long list of conditions — eczema, PMS, breast pain, rheumatoid arthritis, and menopause among them. Being widely sold is not the same as being proven to work.

What the science says, claim by claim

Claim: EPO reduces hot flashes and night sweats

This is the headline claim, and it is where the evidence is weakest. According to the U.S. National Center for Complementary and Integrative Health (NCCIH), "very little research has been done" on evening primrose oil for menopausal symptoms, "so no conclusions can be reached about their effectiveness." NCCIH's broader assessment is blunt: there is "not enough evidence to support the use of evening primrose oil for any health condition."

The individual studies bear this out. Most are small, short, and of low methodological quality, and their results conflict — some report a modest drop in how severe hot flashes feel, others find no meaningful difference from placebo. That pattern — a few small trials pulling in different directions — is exactly what a shaky evidence base looks like.

Claim: There's a strong "natural fatty acid" mechanism

The GLA story is plausible on paper, but the most rigorous test of GLA in humans is telling. A 2013 Cochrane systematic review pooled 27 trials of oral evening primrose oil and borage oil for eczema — the condition where EPO has been studied most — and found no meaningful benefit over placebo. If the fatty-acid mechanism doesn't hold up where it has been studied most, it is hard to lean on it for hot flashes, where it has barely been studied at all.

Claim: Leading guidelines back it

They don't. The Menopause Society's 2023 position statement on non-hormone therapies reviewed dietary supplements for hot flashes and does not recommend them for that purpose. The UK's NHS makes the same point about herbal and complementary products for menopause: there is "very little evidence to show how well they work, or how safe they are." For symptomatic relief with better evidence behind it, see our guide to non-hormonal menopause treatments and hormone replacement therapy.

Strength of evidence: Insufficient

Using a simple four-step scale — Strong, Moderate, Limited, Insufficient — the evidence that evening primrose oil relieves menopausal hot flashes rates Insufficient. That is not the same as "proven not to work"; it means the studies are too few, too small, and too inconsistent to say either way. EPO sits alongside several other popular herbs here — the same caveats apply to black cohosh and red clover, which also lack convincing evidence for hot flashes.

Safety and interactions

For most healthy adults, short-term use of evening primrose oil is generally well tolerated. The most common side effects are mild and digestive — stomach upset, nausea, headache, or loose stools. A few interactions are worth knowing about:

  • Blood thinners and antiplatelet drugs. EPO may slightly increase bleeding risk, so it is often flagged for people taking warfarin or similar medicines.
  • Surgery. Because of that same bleeding concern, it is commonly paused before planned procedures.
  • Seizure threshold. There is a long-standing caution about combining EPO with certain medications in people prone to seizures, though the evidence is thin.

"Natural" products are not quality-controlled the way medicines are, so purity and strength can vary between brands. None of this is a personalized recommendation — your own medications and health history matter.

The honest bottom line

Evening primrose oil is inexpensive and low-risk for most people, but the case that it eases hot flashes or other menopause symptoms rests on weak, inconsistent evidence — and no major guideline endorses it. If your symptoms are disrupting daily life, options with stronger support exist. You can map how you're feeling with our menopause symptom score, read up on what actually helps hot flashes and which supplements have the best evidence, and explore our full menopause hub. Before you start or stop any supplement or medication — especially if you take a blood thinner — talk to your clinician about what is right for you.