Herb & supplement monograph

Evening Primrose Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Evening Primrose interacts with medications. The heart of this page is the interaction list — every drug Evening Primrose is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Evening Primrose is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Evening Primrose Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Evening Primrose drug interaction appears low for most people. None of the listed interactions are rated major, and nearly all rest on theoretical concerns or isolated case reports rather than well-documented human studies.

Interactions deserving the most attention

The combinations most worth watching involve narrow-margin medicines. With blood thinners, including antiplatelet drugs, evening primrose oil may modestly raise bleeding risk because a fatty acid it contains can slow clotting. A single case report suggests it may lower lithium levels, which matters because lithium needs steady blood levels to work. There is also an older concern that it could lower the seizure threshold in people taking phenothiazines, and one case report of raised lopinavir levels in a patient on Kaletra.

What the rest of the list means

Evening primrose appears alongside a long roster of medications largely because lab research suggests it may affect an enzyme the body uses to clear certain drugs. That kind of finding is theoretical, and it has not been shown to cause meaningful changes in people. In short, a long list reflects caution in the data, not proof that each combination is harmful.

Check your medications against Evening Primrose

Based on HelloPharmacist’s Evening Primrose interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Evening Primrose

234 medications have a known interaction with Evening Primrose, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Evening Primrose using our pharmacist-reviewed interaction data.

AI summaries are generated from our Evening Primrose interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Evening Primrose combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Evening Primrose affects

Every type of medication (drug category) Evening Primrose is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 5 drug categories Evening Primrose interacts with

Anticoagulant/antiplatelet DrugsLithiumLopinavir/ritonavir (kaletra)PhenothiazinesCytochrome P450 2c9 (cyp2c9) Substrates

Anticoagulant/Antiplatelet Drugs

Theoretically, evening primrose oil may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Evening primrose oil contains gamma linolenic acid (GLA). There is preliminary clinical evidence that GLA can reduce platelet aggregation and prolong bleeding time.

Likelihood Possible Evidence D

Lithium

Theoretically, concomitant use of lithium with evening primrose oil might decrease lithium levels and effects.
In a case report, a patient on a stable dose of lithium for 10 years experienced a reduction in lithium levels after taking evening primrose oil 500 mg daily. Baseline levels were 0.69 mmol/L, which decreased to 0.37 mmol/L after 2 months and 0.23 mmol/L after 3 months of use. Lithium levels increased within 6 weeks of discontinuing evening primrose oil, to 0.73 mmol/L; no clinical effects were noted.

Likelihood Possible Evidence D

Lopinavir/Ritonavir (Kaletra)

Theoretically, evening primrose oil might increase the levels and effects of lopinavir.
In a case report, an HIV patient who took evening primrose oil (Efamol) along with lopinavir/ritonavir experienced an increase in serum levels of lopinavir to 15.2 mg/L. Six weeks after discontinuing evening primrose oil, levels of lopinavir returned to the normal range of 5-10 mg/L. When re-challenged with evening primrose oil for a week, the patient's lopinavir levels increased from 6.69 to 8.11 mg/L. It is suspected that evening primrose oil increases levels of lopinavir by inhibiting cytochrome P450 3A4 (CYP3A4), which metabolizes lopinavir. However, this effect has not been reported in other research.

Likelihood Possible Evidence D

Phenothiazines

Theoretically, taking evening primrose oil with phenothiazines might increase the risk of convulsions.
Evening primrose oil contains gamma-linolenic acid (GLA). There is some concern that taking supplements containing GLA might cause seizures, or lower the seizure threshold, when taken with phenothiazines. In one report, three patients with schizophrenia who had received phenothiazines developed EEG changes suggestive of temporal lobe epilepsy after starting treatment with GLA, although none experienced an actual seizure. In another report, two patients with schizophrenia who were stabilized on phenothiazines developed seizures when evening primrose oil 4 grams daily was added. One of these patients had a prior history of seizures. It is unclear whether evening primrose oil had any additive epileptogenic effects with the phenothiazines; there is no evidence that taking evening primrose oil alone causes seizures.

Likelihood Possible Evidence D

Cytochrome P450 2C9 (Cyp2C9) Substrates

Theoretically, evening primrose may increase the levels and clinical effects of CYP2C9 substrates.
In vitro research shows that linoleic acid, a constituent of evening primrose oil, inhibits CYP2C9.

Likelihood Possible Evidence D

Monograph

Evening Primrose: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Evening primrose oil is a seed oil rich in gamma-linolenic acid (GLA), an omega-6 fatty acid, that is popularly used for skin conditions, PMS, and breast pain. The evidence behind most of these uses is mixed or weak, and it is not proven to be a reliable treatment for any condition. It is generally well tolerated for short-term use, but talk to your pharmacist or doctor before starting it, especially if you are pregnant or have a bleeding disorder.

Scientific name: Oenothera biennis
Family: Onagraceae
Part used: Seed oil
Common forms: Capsules, softgels, oil, topical creams

People commonly use it for

Eczema and skin health
PMS symptoms
Breast pain (mastalgia)
Menopause symptoms
Inflammation
Diabetic nerve pain

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Generally well tolerated short-term, but quality evidence and long-term safety data are limited.

PregnancyPossibly Safe

When evening primrose oil is used orally and appropriately. In small studies of evening primrose oil for pre-eclampsia, 4 grams has been used orally d...

Read the full pregnancy detail

BreastfeedingPossibly Safe

When evening primrose oil is used orally. Supplementation with evening primrose oil during lactation results in the secretion of high levels of the co...

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Evening primrose (Oenothera biennis) is a plant native to North and Central America that is now found in many parts of the world. It has bright yellow flowers that tend to open in the evening, which is how it got its name.

The seeds of the plant are pressed to make evening primrose oil. This oil is rich in gamma-linolenic acid (GLA), an omega-6 fatty acid, along with linoleic acid. Evening primrose oil is most often sold as capsules or softgels, and it is sometimes used in creams applied to the skin.

People take it for a range of reasons, most commonly for skin conditions like eczema, for premenstrual syndrome (PMS), and for breast tenderness. Products are often standardized by their GLA and linoleic acid content.

How it works

The main active ingredient in evening primrose oil is gamma-linolenic acid (GLA), an omega-6 fatty acid. The body can convert GLA into substances that may affect inflammation and the way cells signal to one another.

The idea behind its use is that GLA may help balance certain inflammatory compounds and support healthy skin barrier function. However, much of this is based on laboratory and animal research or on theory, and it does not always translate into clear benefits in people.

Effectiveness

Does Evening Primrose work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 45 uses evaluated

2 Leans ineffective 43 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Possibly Ineffective Asthma