Evening primrose oil

What it is

Evening primrose oil is the oil from the seeds of the evening primrose plant, sold over the counter in capsules. Its constituents are omega-6 fatty acids, chiefly linoleic acid and gamma-linolenic acid, with vitamin E; a published capsule ingredient list also records gelatin and glycerol as the capsule material. Gamma-linolenic acid is a precursor to prostaglandins, which is the basis of the anti-inflammatory claims made for it. Borage oil is the other gamma-linolenic acid oil tested alongside it in trials.

What the research says

For the two uses with the most trial data, the answer is that it does not work. A Cochrane review of 27 randomised trials in 1,596 participants found oral evening primrose oil and borage oil had no effect on eczema, and the authors wrote that further studies would be hard to justify. A systematic review of 13 trials in 1,752 women with breast pain found evening primrose oil no different from placebo, topical NSAIDs, danazol or vitamin E. NCCIH's position is that there is not enough evidence to support its use for any health condition. One small 6-week randomised trial in 56 menopausal women did find hot flush severity improved more than on placebo, which is the main positive signal and rests on a single small short study. Side effects are mostly gastrointestinal and were as common on placebo as on the oil; the documented interaction signals are a case report of falling lithium levels and a warning about bleeding on warfarin.

Evidence grade: Not supported by the research.

What goes wrong

In the Cochrane eczema trials, evening primrose oil and borage oil caused the same fairly common mild transient adverse effects as their placebos, mainly gastrointestinal. (Source 1)

• Systematic review, Moderate certainty.
• Size: 27 studies, 1,596 participants.
• Who: people with eczema in short-term trials.
• How long: short-term.
• Result: no rates given; described as fairly common, mild and transient, mainly gastrointestinal, and equal to placebo.
• Funding: not stated in the abstract.

In these studies, along with the placebos, EPO and BO have the same, fairly common, mild, transient adverse effects, which are mainly gastrointestinal.

The Cochrane review flags that the trials were too short to assess long-term safety and cites a case report of inflammation, thrombosis and immunosuppression after prolonged use, plus a report of increased bleeding on warfarin. (Source 1)

• Systematic review, Very low certainty.
• Size: single case report and one further study cited within the review.
• Who: people taking evening primrose oil for more than one year; people on warfarin.
• How long: more than one year in the cited case report.
• Result: no rates given; described as a potential risk of inflammation, thrombosis and immunosuppression, and increased bleeding with warfarin.
• Funding: not stated in the abstract.

A case report warned that if EPO is taken for a prolonged period of time (more than one year), there is a potential risk of inflammation, thrombosis, and immunosuppression; another study found that EPO may increase bleeding for people on Coumadin® (warfarin) medication.

A case report describes serum lithium falling below the therapeutic range while a woman took evening primrose oil 500 mg daily, and recovering after it was stopped. (Source 2)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: a 38-year-old woman on lithium carbonate 800 mg daily with nortriptyline and thyroxine.
• How long: 5 months of evening primrose oil in total.
• Result: serum lithium 0.69 mmol/l at baseline, 0.37 mmol/l after 2 months, 0.23 mmol/l after 3 months, and 0.73 mmol/l six weeks after stopping, with no other medication change.
• Funding: not stated.

Yet, on regular 3-monthly check-up of lithium levels, after taking EPO for 2 months, a reduction in serum lithium level was noted (0.37 mmol/l).

The authors of that report say it is the first published account of an evening primrose oil and lithium interaction and that the timing points to a real interaction. (Source 3)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: a woman on long-term lithium augmentation.
• How long: 5 months.
• Result: lithium level fell during co-intake and recovered immediately after cessation, with no other change in medication, compliance or medical status.
• Funding: not stated.

In our patient, lithium levels dropped following co-intake of EPO. They improved immediately following EPO cessation.

The same letter records, as background, that evening primrose oil lowers the seizure threshold in patients taking phenothiazines. (Source 2)

• Case report, Very low certainty.
• Size: not applicable; a background statement in a case report letter.
• Who: patients taking phenothiazine antipsychotics.
• How long: not stated.
• Result: no rate or effect size given.
• Funding: not stated.

EPO decreases seizure threshold for patients taking phenothiazines; however, there are no reported interactions between EPO and lithium carbonate.

POSITION: NCCIH (November 2024) states evening primrose oil is probably safe for most adults orally, is generally well tolerated, and most commonly causes gastrointestinal symptoms. (Source 4)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: adults, with children flagged as less well studied.
• How long: not applicable.
• Result: no rates given; abdominal pain, nausea or diarrhoea named as the most common side effects.
• Funding: US government agency page.

Evening primrose oil is probably safe for most adults when taken orally. Less is known about its safety for children. Evening primrose oil is generally well tolerated. The most common side effects are gastrointestinal symptoms such as abdominal pain, nausea, or diarrhea.

What the evidence supports

The same review found evening primrose oil did not increase adverse events compared with placebo or other treatments. (Source 5)

• Systematic review, Low certainty.
• Size: 1,752 randomised patients across 13 trials.
• Who: women with mastalgia.
• How long: not stated in the abstract.
• Result: no increase in nausea, abdominal bloating, headache, giddiness, weight gain or altered taste.
• Funding: not stated in the abstract; risk of bias unclear or high for allocation concealment and blinding in several trials.

The EPO does not increase adverse events, such as nausea, abdominal bloating, headache or giddiness, increase weight gain, and altered taste compared to a placebo or other treatments.

A small randomised trial found hot flush severity, but not frequency or duration, improved more on evening primrose oil than on placebo. (Source 6)

• Randomized trial, Low certainty.
• Size: 56 menopausal women aged 45-59.
• Who: menopausal women with hot flushes.
• How long: 6 weeks.
• Result: improvement in hot flash frequency, severity and duration of 39%, 42% and 19% on evening primrose versus 32%, 32% and 18% on placebo; only severity significantly better (P < 0.05)
• Funding: not stated in the abstract; single centre, small sample, 6 weeks only.

Although all three characters of hot flash was ameliorated in evening primrose arm, only its severity was significantly better in this arm compared with placebo group (P < 0.05).

What the evidence does not support

A Cochrane review found oral evening primrose oil did not improve global eczema symptoms compared with placebo on either participant or doctor ratings. (Source 7)

• Systematic review, Moderate certainty.
• Size: 176 participants across 7 trials (participant-rated) and 289 participants across 8 trials (doctor-rated), within a review of 27 studies and 1,596 participants.
• Who: adults and children with eczema.
• How long: short-term trials; the review notes it cannot address long-term use.
• Result: participant-rated MD -2.22 (95% CI -10.48 to 6.04) on a 0-100 visual analogue scale; doctor-rated MD -3.26 (95% CI -6.96 to 0.45)
• Funding: not stated in the abstract; 67% of studies at low risk for sequence generation, 44% for allocation concealment, 59% for blinding.

EPO failed to significantly increase improvement in global eczema symptoms as reported by participants on a visual analogue scale of 0 to 100 (MD ‐2.22, 95% CI ‐10.48 to 6.04, 176 participants, 7 trials)

The Cochrane authors concluded that oral evening primrose oil and borage oil are not effective treatments for eczema. (Source 1)

• Systematic review, Moderate certainty.
• Size: 27 studies, 1,596 participants.
• Who: people with eczema.
• How long: short-term trials.
• Result: improvement similar to the placebos used in the trials.
• Funding: not stated in the abstract.

Oral borage oil and evening primrose oil lack effect on eczema; improvement was similar to respective placebos used in trials. Oral BO and EPO are not effective treatments for eczema.

A systematic review and meta-analysis of 13 trials found evening primrose oil no better than placebo or active comparators for breast pain. (Source 5)

• Systematic review, Low certainty.
• Size: 1,752 randomised patients across 13 trials.
• Who: women with mastalgia.
• How long: not stated in the abstract.
• Result: no difference in breast pain reduction versus topical NSAIDs, danazol or vitamin E; no difference in the number achieving pain relief versus placebo or other treatments.
• Funding: not stated in the abstract; eight trials lacked documented allocation concealment and most did not describe participant blinding.

The results showed that EPO has no difference to reduce breast pain compared to topical NSAIDS, danazol, or vitamin E. The number of patients who achieved pain relief was no different compared to the placebo or other treatments.

POSITION: NCCIH (page updated November 2024) states there is not enough evidence to support evening primrose oil for any health condition. (Source 8)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: general population.
• How long: not applicable.
• Result: no numbers given; the page names atopic dermatitis and breast pain as not helped, and rheumatoid arthritis, PMS and menopause symptoms as insufficiently studied.
• Funding: US government agency page.

There's not enough evidence to support the use of evening primrose oil for any health condition.

Where the research disagrees

Whether evening primrose oil helps menopausal hot flushes

• Farzaneh and colleagues, Archives of Gynecology and Obstetrics, 2013, single 6-week randomised trial in 56 menopausal women: Although all three characters of hot flash was ameliorated in evening primrose arm, only its severity was significantly better in this arm compared with placebo group (P < 0.05). (Source 6)
• NCCIH, page updated November 2024, agency evidence summary across the trial literature: There's insufficient evidence to show whether evening primrose oil is helpful for other conditions, such as rheumatoid arthritis, PMS, and menopause symptoms. (Source 8)

How much

• Reference intake: No health authority sets a reference intake for evening primrose oil or for gamma-linolenic acid; it is not an essential nutrient and has no RDA or AI. NCCIH (November 2024) states there is not enough evidence to support its use for any health condition. (Source 8)
• Upper limit: No tolerable upper intake level or acceptable daily intake has been set for evening primrose oil. NCCIH (November 2024) states only that it is probably safe for most adults taken orally and that less is known about its safety for children. (Source 4)
• Studied: A 6-week randomised trial in 56 menopausal women gave two 500 mg evening primrose capsules per day, 90 capsules in total. (Source 6)
• Studied: A published case report describes a woman taking evening primrose oil 500 mg daily capsules for five months alongside lithium carbonate 800 mg daily. (Source 2)

A common belief, and what the research shows

The belief: Evening primrose oil is a proven treatment for eczema.

What the research shows: The Cochrane review of 27 randomised trials in 1,596 participants concluded the opposite: "Oral borage oil and evening primrose oil lack effect on eczema; improvement was similar to respective placebos used in trials. Oral BO and EPO are not effective treatments for eczema." NCCIH states "Evening primrose oil, taken orally, has not been shown to be helpful for relieving symptoms of atopic dermatitis."

Questions and answers

What is it?

Evening primrose oil is the oil pressed from evening primrose seeds and sold over the counter in capsules. A published ingredient list for one capsule records omega-6 fatty acids including linoleic acid, natural vitamin E and D-alpha tocopherol, with gelatin and vegetable glycerol as capsule material. The constituent it is usually sold for is gamma-linolenic acid. (Source 9)

What does it do in the body?

The proposed mechanism is that gamma-linolenic acid, an omega-6 fatty acid, is a precursor to prostaglandins, which act as anti-inflammatory mediators. That is the rationale behind the inflammatory and hormonal claims made for the oil. It remains a mechanism rather than a demonstrated clinical effect, since the trials in eczema and breast pain were null. (Source 2)

Is it good or bad for you?

For the two best-studied uses it is neither: the trials are null. A Cochrane review of 27 randomised trials found no effect on eczema, and a review of 13 trials found no effect on breast pain beyond placebo. One small 6-week trial found hot flush severity improved. Tolerability is good, with side effects mainly gastrointestinal and no more common than on placebo, but long-term safety was never tested and there are case-level signals with lithium and warfarin. (Source 1)

How do you get more of it?

It is taken as capsules. The 6-week randomised trial in menopausal women gave two 500 mg evening primrose capsules a day, and the published lithium case report describes 500 mg daily capsules. These are descriptions of what studies and case reports used, not recommendations. (Source 6)

If it is harmful, what reduces it?

Stopping the capsules is what the literature records. In the published lithium case report, the serum lithium level returned to the therapeutic range six weeks after the evening primrose oil was discontinued, with no other medication change. There is no described way to clear it faster. (Source 10)

Why might someone be low in it or missing it?

The question does not apply in the usual sense: evening primrose oil is not an essential nutrient, there is no requirement for it, and no deficiency state has been described. Nobody is low in evening primrose oil. NCCIH's summary is that there is not enough evidence to support its use for any health condition at all. (Source 8)

We searched: Searched Cochrane, PMC and NCCIH for evening primrose oil or gamma-linolenic acid deficiency, requirement and status; no literature defines a deficiency of either.

Which whole foods contain it or feed it?

No everyday whole food supplies evening primrose oil; it is an extracted seed oil. The only comparable gamma-linolenic acid oil that appears in the trial literature alongside it is borage oil, which the same Cochrane review tested in 8 studies and also found ineffective for eczema. The sources we reached do not list whole foods providing it. (Source 7)

We searched: Searched PMC, Cochrane and NCCIH for whole food sources of evening primrose oil and gamma-linolenic acid; the reviews we reached name only the extracted seed oils, and the PMC review of evening primrose oil composition would not load past the reCAPTCHA gate.

What happens if you do not have it?

Nothing is known to happen, because nothing in the body depends on it. Not taking it means forgoing effects that the best trials did not find: NCCIH states it has not been shown to help atopic dermatitis, and the Cochrane review found no effect on eczema at all. (Source 8)

We searched: Searched Cochrane, PMC and NCCIH for consequences of not taking evening primrose oil; no study treats absence as an exposure, and no deficiency syndrome exists.

How can you test for it?

There is no validated clinical test for evening primrose oil intake or status. The only measurable marker recorded on the NCCIH page is that taking it while breastfeeding raises the concentration of gamma-linolenic acid in breast milk, which is a research observation rather than a diagnostic test. No blood test is offered or interpreted clinically. (Source 4)

We searched: Searched Cochrane, PMC and NCCIH for a gamma-linolenic acid or evening primrose oil biomarker or status test; only breast-milk GLA concentration appears, and no reference ranges are given.

References

1. Cochrane Database of Systematic Reviews. Oral evening primrose oil and borage oil for eczema - Abstract, Authors' conclusions. 2013. PMID 23633319, DOI 10.1002/14651858.CD004416.pub2. Read the source
2. Therapeutic Advances in Psychopharmacology. Evening primrose oil reducing serum lithium concentration - background and case presentation. 2016. PMID 27721973, DOI 10.1177/2045125316658617. Read the source
3. Therapeutic Advances in Psychopharmacology. Evening primrose oil reducing serum lithium concentration - authors' interpretation. 2016. PMID 27721973, DOI 10.1177/2045125316658617. Read the source
4. National Center for Complementary and Integrative Health (NCCIH), NIH. Evening Primrose Oil - Usefulness and Safety (what we know about safety). 2024. Read the source
5. International Journal of Environmental Research and Public Health. A Systematic Review and Meta-Analysis of the Efficacy of Evening Primrose Oil for Mastalgia Treatment. 2021. PMID 34200727, DOI 10.3390/ijerph18126295. Read the source
6. Archives of Gynecology and Obstetrics. The effect of oral evening primrose oil on menopausal hot flashes: a randomized clinical trial. 2013. PMID 23625331, DOI 10.1007/s00404-013-2852-6. Read the source
7. Cochrane Database of Systematic Reviews. Oral evening primrose oil and borage oil for eczema - Abstract, Main results. 2013. PMID 23633319, DOI 10.1002/14651858.CD004416.pub2. Read the source
8. National Center for Complementary and Integrative Health (NCCIH), NIH. Evening Primrose Oil - Usefulness and Safety (what we know about effectiveness). 2024. Read the source
9. Therapeutic Advances in Psychopharmacology. Evening primrose oil reducing serum lithium concentration - capsule ingredients and limitations. 2016. PMID 27721973, DOI 10.1177/2045125316658617. Read the source
10. Therapeutic Advances in Psychopharmacology. Evening primrose oil reducing serum lithium concentration - course after discontinuation. 2016. PMID 27721973, DOI 10.1177/2045125316658617. Read the source