Evening primrose oil for PMDD: does it work?

No trial has tested evening primrose oil (EPO) in women or girls with a confirmed PMDD diagnosis, the kind made with daily symptom ratings over at least two cycles. Every trial on EPO and premenstrual symptoms has studied PMS instead, a different and far more common pattern.

For PMS, the evidence is mixed rather than clearly positive. The best-designed studies identified by a 1996 review of EPO trials for PMS [3], and a separate 1990 Australian crossover trial [4], found no real difference between EPO and placebo. Two more recent Iranian trials found the opposite, with EPO beating placebo by a wide margin [7] [8].

The honest summary is that EPO has no PMDD-specific evidence, and the PMS evidence leans more often toward no benefit over placebo than toward a real effect.

The clearest picture comes from comparing trial quality. A 1996 review [3] pooled every placebo-controlled EPO trial available at the time and found only two solid enough to trust; both showed no benefit for PMS.

A 1990 Australian trial gave 38 women EPO and placebo across six cycles. Symptom scores fell in both groups, and the authors concluded the improvement was a placebo effect [4].

Two Iranian trials, run at the same university, found EPO did better than placebo. An 80-student trial in 2018 found scores drop from roughly 61 to 21 points with EPO, against a rise in the placebo group [8]. A 120-student trial in 2019 found EPO outperformed both placebo and vitamin B6 [7]. Neither trial used a DSM-5 PMDD diagnosis.

A 2024 systematic review of EPO across inflammatory conditions, including PMS, concluded it hasn't demonstrated effectiveness there [1].

Trials on EPO for premenstrual symptoms measured results after two to six menstrual cycles, not after a few days. A review of EPO research for women's health conditions says not to expect an immediate response, and recommends regular use for 4 to 6 months before judging the effect [6].

In the trials, doses ranged from 1,000 mg taken twice daily (2,000 mg total) for PMS [7] [8], up to 3,000 mg daily for cyclical breast pain, measured over six months [5]. The 1990 Australian trial found some symptom improvement appeared within the first cycle, but it didn't separate from the placebo effect over six cycles of use [4].

If you're trying EPO, give it a full cycle or two before deciding, and track your symptoms daily so you can see a real pattern rather than guessing from memory. Our guide to how long evening primrose oil takes to work and dosage page go through the specifics.

Evening primrose oil was generally well tolerated across the trials reviewed here. The 2018 Iranian trial specifically noted few side effects in the EPO group [8], and a 2024 systematic review across several conditions didn't flag major safety concerns, even though it didn't find a PMS benefit [1].

Reported side effects in EPO research, across conditions, are typically mild:

• Headache
• Nausea or an upset stomach
• Soft stools

These tend to ease when you take EPO with food. None of the trials covered here reported serious adverse effects, though the trials were small and side effects weren't always tracked in detail.

Our evening primrose oil side effects page covers what's been reported in more depth, including effects on mood.

If you're pregnant, breastfeeding, or trying to conceive, evening primrose oil hasn't been well studied for you outside of late pregnancy.

A 2018 trial gave EPO to women at 40 weeks of pregnancy to see if it affected labor, and found no difference in labor length, delivery outcomes, or newborn health compared with placebo [2]. That trial was done under medical supervision, close to delivery; EPO hasn't been studied the same way earlier in pregnancy.

These situations call for extra caution too:

• Take other medication regularly
• Have a bleeding disorder or are due for surgery
• Have reacted to evening primrose oil or similar supplements before

A doctor can weigh EPO against what you're already taking and decide if it fits.

Evening primrose oil isn't a first-line treatment for PMDD. Guidelines point to options with stronger evidence instead: SSRIs, which some people take only in the two weeks before their period, certain hormonal contraceptives, and cognitive behavioral therapy (CBT). A doctor decides which combination fits your history and symptoms.

If you're not sure whether what you're feeling fits PMS or PMDD, our guide to PMDD walks through how the diagnosis is made and what's different about it. For a fuller rundown of what actually has evidence behind it, see PMDD treatment: what actually helps and PMS supplements: what actually helps.

Daily tracking matters here. Whatever you try, note your mood and physical symptoms every day for at least two cycles so you, and your doctor, can see if a real pattern shows up, rather than guessing from a single week before your period.

Evening primrose oil, if it works at all, works slowly over months. It won't help with a hard moment happening right now. For that, you need something faster.

1. Leave the room if you're mid-argument, and say you'll come back in 20 minutes.
2. Breathe out for six counts, longer than you breathe in, for a minute or two.
3. Write down exactly what happened, in your own words, before you respond to anyone.
4. Wait before you send a message or make a decision you can't take back.

If you want somewhere to put the fight before you answer, Niyora is a PMS and PMDD support app. Its Moon feature lets you write down what happened, see it from another side, and draft a reply you can hold onto for 20 minutes before you decide whether to send it.