--- title: Side effects of evening primrose oil, including mood description: Side effects of evening primrose oil are usually mild, like an upset stomach or headache. Here's what trials found about mood, weight, and stopping. url: https://niyora.com/treatments/evening-primrose-oil-side-effects/ --- - [Niyora](https://niyora.com/) - [Treatments](https://niyora.com/treatments/) - Evening primrose oil side effects, including mood Treatments # Evening primrose oil side effects, including mood The most common side effects of evening primrose oil are mild: stomach upset, headache, and occasional nausea. Trials don't show it causing weight gain or sedation, and for PMS mood symptoms it hasn't outperformed placebo. Serious problems are rare, and it's a mild blood thinner, so pregnancy, blood-thinning medication and seizure disorders are the main things to flag before you start. Updated 13 October 2026 Niyora editorial Limited evidence Strength of evidence Limited Only small or early studies so far. - None - Limited - Mixed - Moderate - Strong ## At a glance - Most trials report only mild side effects: an upset stomach, nausea, loose stools, or headache. - No trial has linked evening primrose oil to weight gain; PMS trials that tracked fluid retention found no difference from placebo. - For PMS mood and anxiety symptoms, evening primrose oil hasn't outperformed placebo in placebo-controlled trials. - It's a mild blood thinner, so pregnancy, blood-thinning medication and seizure disorders are the main things to flag before you start. - If you don't notice any benefit after four to six months, or side effects don't ease, it's reasonable to stop. ## Strength of evidence Limited evidence - None - Limited - Mixed - Moderate - Strong Most data comes from small, short trials tracking PMS symptom scores, not systematic side-effect reporting. Evening primrose oil looks about as well tolerated as placebo, with mild stomach upset or headache the main complaints, no link to weight gain or sedation, and benefit in only one trial, for breast pain. ## What are the side effects of evening primrose oil? Most people who take evening primrose oil notice only mild side effects, if any. Across clinical trials covering premenstrual syndrome, breast pain, eczema and other conditions, the complaints that come up most often are: - An upset stomach - Nausea - Loose stools - Occasional headache A 2024 systematic review in BMC Complementary Medicine and Therapies looked at evening primrose oil across several inflammatory conditions and found mixed evidence for benefit, and the review itself didn't report systematically on adverse events across the trials it covered. The review didn't set out to track side effects systematically, so this isn't a formal safety verdict. A separate review of evening primrose oil in women's health, covering PMS, mastalgia and menopausal symptoms, found it generally needs four to six months of regular use before any benefit shows, and and didn't address safety as a specific outcome in the studies it covered. That's the headline on safety. It doesn't mean the oil works for what you're taking it for, which is a separate question covered on our [evening primrose oil overview page](https://niyora.com/treatments/evening-primrose-oil/). ## Can evening primrose oil cause weight gain? There's no trial evidence that evening primrose oil causes weight gain. None of the placebo-controlled PMS trials report it as a side effect, and the ones that measured bloating and fluid retention as a symptom category found no real difference between evening primrose oil and placebo. A 1990 crossover trial in the Medical Journal of Australia tracked ten PMS symptoms, including fluid retention, in 38 women over six menstrual cycles. Scores improved on both the active treatment and the placebo, with no significant difference between them. That pattern, improvement that tracks with placebo rather than the active ingredient, shows up across most evening primrose oil trials for PMS. If you're thinking of the bloated, heavier feeling that shows up before a period, that's a separate issue, a premenstrual symptom, not a side effect of a supplement. Our page on [PMS treatment](https://niyora.com/treatments/pms-treatment/) covers what actually helps with that. ## Is evening primrose oil safe? For most healthy adults, evening primrose oil is considered low risk when taken at typical doses for a few months. The safety concerns that come up are specific rather than common. It's a mild blood thinner, so doctors usually advise stopping it before surgery, and the same caution applies if you're already on anticoagulant medication. People with a seizure disorder are often told to avoid it, since gamma-linolenic acid, its main active compound, has a theoretical link to a lowered seizure threshold. Pregnancy is also a reason for caution, since safety data is limited. One small trial gave evening primrose oil to women in the final week of pregnancy and found no difference in labor length or newborn outcomes compared to placebo, but that single short trial doesn't establish it as safe for routine use earlier in pregnancy. If you take prescription medication for a chronic condition, mention evening primrose oil to whoever prescribes it. It's about taking a supplement the same way you'd take anything else that affects your body, with a clear sense of what it does and who should check first. ## Can evening primrose oil affect your mood? Evening primrose oil hasn't been shown to reliably change mood in either direction. A 1988 trial in Human Psychopharmacology focused specifically on women with PMS-related anxiety and depression, the group most likely to notice a mood effect if there was one. Depression and anxiety scores improved over the two months of the trial, but they improved just as much on placebo as on evening primrose oil. Larger reviews of evening primrose oil for PMS land in the same place. A 1996 systematic review found the two best-controlled trials showed no benefit for psychological symptoms, and a 2022 literature review described the results as contradictory, with no consistent pattern of improvement. So evening primrose oil hasn't been shown to worsen mood, and it hasn't been shown to reliably improve it either, beyond what a placebo does. If what you're after is a way to manage the anger or sadness that shows up on a hard day, that's a different problem than finding the right supplement. Niyora is a PMS and PMDD support app. Its Moon feature lets you write down what happened, see it from another angle, calm down, and draft a reply you can hold onto for 20 minutes. ## How long do side effects last, and when should you stop? When side effects happen, they tend to show up early and stay mild, an upset stomach or headache in the first week or two, easing as your body adjusts or once you stop. There's no trial data suggesting side effects build up or get worse the longer you take it. Judging whether evening primrose oil is working is a separate timeline. A review of its use in women's health conditions found that an immediate response shouldn't be expected, and recommended regular use for four to six months before deciding whether it's helping. If you've reached that point with no real change in your symptoms, it's reasonable to stop. When to see a doctor If you notice unusual bruising or bleeding, a headache that's far worse than usual, or stomach pain that doesn't ease within a day or two, stop taking it and call your doctor. ## What are the alternatives? Evening primrose oil isn't the only option, and for premenstrual mood symptoms specifically, it isn't the one with the strongest evidence. Clinical guidelines for PMS and PMDD point to a short list of treatments with better trial support: SSRIs (which some people take only in the second half of the cycle), certain hormonal contraceptives, and cognitive behavioral therapy. A doctor decides what fits your situation and history. One pocket of evidence looks a little better: a six-month, placebo-controlled pilot trial of evening primrose oil for cyclical breast pain found an improvement in worst-pain scores within the EPO group over time, but the difference from placebo wasn't statistically significant on direct comparison. If breast tenderness before your period is your main complaint rather than mood or anger, that's worth knowing. If you want to try evening primrose oil anyway, our [dosage guide](https://niyora.com/treatments/evening-primrose-oil-dosage/) covers how much and when, and our page on [PMS supplements](https://niyora.com/techniques/supplements/) puts it alongside the other options the evidence actually supports. For a closer look at what it can and can't do, see our pages on [evening primrose oil for PMS](https://niyora.com/treatments/evening-primrose-oil-for-pms/) and [evening primrose oil for PMDD](https://niyora.com/treatments/evening-primrose-oil-for-pmdd/). Many people try a supplement for a few cycles, track what actually changes, and adjust from there. From the research library ## Research on evening primrose oil 38 studies in the library look at evening primrose oil in PMS and PMDD. They were published from 1983 to 2026, and each one is summarised in plain English. 38 studies, 1983 to 2026 How strong the studies are Strong study design 4 Moderate study design 18 Early or limited evidence 16 - [Systematic review, 2009Which herbs, vitamins and minerals help treat PMS?Only calcium has good evidence to work for PMS. Chasteberry and vitamin B6 may help, but most of the 62 products people try lack proper research.Strong study design](https://niyora.com/research/papers/herbs-vitamins-and-minerals-in-the-treatment-of-premenstrual-syndrome-a-2009/) - [Systematic review, 2007What treatments work for premenstrual syndrome?Many treatments have been studied for PMS, but researchers face a major challenge: there is no standard way to measure symptom severity, making it difficult to know which treatments truly work.Strong study design](https://niyora.com/research/papers/premenstrual-syndrome-2007/) - [Study, 2002Which PMS treatments have good scientific evidence?Calcium at 1200 mg daily and certain antidepressants have good evidence of working. Many popular treatments like vitamin B6, evening primrose oil, and birth control pills lack strong evidence. Some treatments like progesterone do not work.Strong study design](https://niyora.com/research/papers/premenstrual-syndrome-evidence-based-treatment-in-family-practice-2002/) - [Randomised trial, 2000Which dietary supplements help PMS?Only calcium has strong evidence from large rigorous trials. Magnesium, vitamin E, and carbohydrate supplements show limited promise but need more research. Vitamin B6 and evening primrose oil have mixed results.Strong study design](https://niyora.com/research/papers/the-potential-for-dietary-supplements-to-reduce-premenstrual-syndrome-pms-2000/) - [Study, 2024Does a combination of evening primrose oil, tocotrienol, and vitamin B6 reduce premenstrual symptoms?Yes. In women with PMS taking this combination for 3 months, premenstrual symptoms improved significantly. The overall PMS score dropped by 61.03%, menstrual pain dropped by 75.20%, and breast tenderness dropped by 82.54%.Moderate study design](https://niyora.com/research/papers/a-real-world-study-to-evaluate-the-effectiveness-of-evening-primrose-oil-in-2024/) - [Randomised trial, 2024Does a herbal soft gel capsule with three oils reduce PMS symptoms?The capsule reduced women's PMS symptoms when compared to their baseline, but was not significantly better than taking sunflower oil.Moderate study design](https://niyora.com/research/papers/effects-of-the-herbal-soft-gel-capsule-containing-pimpinella-anisum-oenothera-2024/) [See all 38 studies on evening primrose oil](https://niyora.com/research/topics/treatment-evening-primrose/) ## Questions people ask Is evening primrose oil safe to take every day? + Evening primrose oil is generally considered safe for most healthy adults when taken daily for a few months. It's a mild blood thinner, so people on anticoagulants, those with a seizure disorder, and anyone pregnant are usually advised to avoid it or use caution. Side effects, when they happen, are usually mild stomach upset or headache. Does evening primrose oil cause weight gain? + Evening primrose oil hasn't been shown to cause weight gain in clinical trials. Trials for PMS that tracked bloating and fluid retention found no real difference between evening primrose oil and placebo. If you're noticing weight changes, they're more likely tied to your cycle itself than to the supplement. Can evening primrose oil make you sleepy? + There's no trial evidence that evening primrose oil causes sleepiness. It isn't sedating the way some supplements or medications are, and the side effects reported in trials are mostly gastrointestinal, like an upset stomach, rather than effects on energy or alertness. If you feel unusually tired, look at other causes first. Who should not take evening primrose oil? + People on blood thinners, anyone with a seizure disorder, and those about to have surgery are usually told to avoid evening primrose oil. It's a mild blood thinner and may interact with anticonvulsant medication. Safety data for pregnancy is also limited, which is another reason for caution. How long does it take for evening primrose oil side effects to show up? + If evening primrose oil causes side effects, they usually show up in the first one to two weeks, as mild stomach upset or headache, and often ease as your body adjusts. Side effects don't typically build up over months of use. If they're getting worse instead of easing, mention that to a doctor. ## Sources - 1. [The effect of Oenothera biennis (Evening primrose) oil on inflammatory diseases: a systematic review of clinical trials](https://doi.org/10.1186/s12906-024-04378-5), BMC complementary medicine and therapies, 2024 - 2. [Evening primrose oil and labour, is it effective? A randomised clinical trial](https://doi.org/10.1080/01443615.2017.1386165), Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology, 2018 - 3. [Is evening primrose oil of value in the treatment of premenstrual syndrome?](https://doi.org/10.1016/0197-2456(95)00082-8), Controlled clinical trials, 1996 - 4. [Evening primrose oil and treatment of premenstrual syndrome](https://doi.org/10.5694/j.1326-5377.1990.tb136857.x), The Medical journal of Australia, 1990 - 5. [Vitamin E and evening primrose oil for management of cyclical mastalgia: a randomized pilot study](https://pubmed.ncbi.nlm.nih.gov/20359269/), Alternative medicine review : a journal of clinical therapeutic, 2010 - 6. [Evening Primrose ( Oenothera biennis ) Oil in Management of Female Ailments](https://doi.org/10.6118/jmm.18190), Journal of menopausal medicine, 2019 - 7. [A double‐blind trial of evening primrose oil in the premenstrual syndrome: Nervous symptom subgroup](https://doi.org/10.1002/hup.470030110), Human Psychopharmacology Clinical and Experimental, 1988 - 8. [Effect of evening primrose oil on the symptoms of premenstrual syndrome. Literature review](https://doi.org/10.51326/ec.5.4.2477363), Enfermería Cuidándote, 2022 Ask AI about this page Copy prompt ChatGPT ↗ Claude ↗ Perplexity ↗ Google AI Mode ↗ Grok ↗ On this page - [What are the side effects of evening primrose oil?](#what-are-the-side-effects-of-evening-primrose-oil) - [Can evening primrose oil cause weight gain?](#can-evening-primrose-oil-cause-weight-gain) - [Is evening primrose oil safe?](#is-evening-primrose-oil-safe) - [Can evening primrose oil affect your mood?](#can-evening-primrose-oil-affect-your-mood) - [How long do side effects last, and when should you stop?](#how-long-do-side-effects-last-and-when-should-you-stop) - [What are the alternatives?](#what-are-the-alternatives) - [Research](#research) - [Questions](#faq) Niyora PMS & PMDD support For the hard moment before your period. Private, no account. [Get it on iPhone](https://apps.apple.com/app/niyora-pms-emotions/id6764561688) ## Keep reading Treatment Evening primrose oil: what it is and whether it helps PMS Treatment Evening primrose oil for PMS: does it work? Treatment Evening primrose oil 1000 mg: dosage, timing, and benefits Treatment Evening primrose oil for perimenopause mood: does it work? Treatment PMS treatment: what actually helps Condition What is PMS? Premenstrual syndrome, explained