© Udo Schröter · CC BY-SA 2.5 · Commons
Oenothera biennis
CautionGemeine Nachtkerze · (Oenothera biennis)
Evening primrose family (Onagraceae)
Description
Its yellow flowers open only in the evening, releasing a delicate scent that draws night-flying pollinators — a display that gives evening primrose its name. Mainly used are the seeds, ripening in autumn, which are pressed into an oil rich in gamma-linolenic acid (7–14%) and linoleic acid (65–80%). The root is also edible and was traditionally eaten as a vegetable or brewed as a tea for digestive complaints. Evening primrose oil is used in folk medicine both externally and internally for skin problems as well as menstrual and joint discomfort. Taken on an empty stomach it can occasionally cause headaches, nausea and diarrhoea. People with epilepsy should avoid high doses, since these may lower the seizure threshold; only quality-controlled preparations should be used.
Critical drug interactions with:
Phenothiazine (Antipsychotika)
The fleshy taproot of first-year plants (October to spring before flowering) is edible. Tastes peppery-spicy, similar to parsnip or salsify. Cooked or prepared like a vegetable. Once the plant flowers the root becomes woody and is no longer suitable for eating.
The small seeds contain 28 % fatty oil, rich in gamma-linolenic acid (GLA, 7–14 %) and linoleic acid (ca. 70 %). Cold-pressed evening primrose oil from the seeds is widely used as a dietary supplement.
Evening primrose oil (GLA-rich) is traditionally taken for atopic dermatitis. GLA promotes synthesis of anti-inflammatory prostaglandins (PGE1). Clinical studies show inconsistent results; the NCCIH finds no clear proof of efficacy.
In folk medicine, mashed roots were applied as a poultice to bruises, contusions, and haemorrhoids. Documented among North American indigenous peoples (Iroquois, Cherokee).
Tea from roots (first harvest, autumn) traditionally used for digestive complaints and obesity. Contains mucilage-like compounds that soothe the intestinal mucosa.
Sources: [5]
Evening primrose oil traditionally used for premenstrual syndrome (PMS), breast pain (mastalgia), and rheumatoid arthritis. The anti-inflammatory mechanism via GLA metabolites is discussed; clinical evidence remains limited.
Evening primrose oil can cause headaches, nausea, and diarrhoea on an empty stomach. High doses lower the seizure threshold in epilepsy. Use only quality-controlled preparations.
⏱ Max continuous use: 12 weeks
Evening primrose oil is sometimes used for labour induction; safety is not conclusively established. Medicinal use only after medical consultation.
Insufficient safety data during lactation. Avoid as a precaution.
Insufficient data for children under 12. Consult a physician.
Drug interactions
Antikoagulantien (z. B. Warfarin, Phenprocoumon)
GLA metabolites inhibit thromboxane A2 and may reduce platelet aggregation; additive effect on bleeding time possible.
Phenothiazine (Antipsychotika)
Combination with phenothiazines may increase risk of seizures.
Contraindications
- Epilepsy (lowers seizure threshold).
- Known hypersensitivity to plants of the evening primrose family (Onagraceae).
Harvested part: seeds (autumn, pressed for oil)
- Time of day:
- Any time of day, as root tissue does not vary by time of day.
- Drying:
- Harvest roots in the first year (rosette stage, October to March) before the plant flowers. Slice thinly and dry at max. 40 °C. Use fresh or store in the refrigerator for a few weeks.
- Storage:
- 6 months — Store dried roots cool, dry, and protected from light.
- Time of day:
- Wait for dry weather; seed capsules split open otherwise.
- Drying:
- Cut seed heads and allow to finish drying over a cloth so remaining seeds fall out. Store seeds cool and dry; press to oil promptly.
- Storage:
- 12 months — Store seed oil dark and cool (refrigerator); oxidises rapidly with light and heat exposure.
- Gamma-Linolensäure (GLA)OtherContent: 7-14 % (im Samenöl)Seed
Rare omega-6 fatty acid; precursor of anti-inflammatory prostaglandins (PGE1). Main active compound of evening primrose oil.
- LinolsäureOtherContent: 65-80 % (im Samenöl)Seed
Essential omega-6 fatty acid; major fatty acid in evening primrose oil.
- EllagsäurePhenolic acidAerial parts
Phenolic compound in herb and root; antioxidant properties.
- GallotannineTanninAerial parts
Tannins in leaves and bark; astringent effect, supporting the folk medicine use for diarrhoea.
- Oenothein A und BTanninAerial parts
Specific ellagitannins of evening primrose; antioxidant and immunomodulatory effects described in vitro.
- SalicylsäurePhenolic acidRoot
Anti-inflammatory phenolic acid; contributes to the folk medicine use for joint complaints.
- Quercetin-GlykosideFlavonoidAerial parts
Flavonoids in flowers and leaves; antioxidant and anti-inflammatory activity.
- [3]MonographEvening Primrose Oil: Usefulness and Safety — NCCIH (NIH)(accessed: 2026-05-22)
- [4]MonographGamma-Linolenic Acid Levels Correlate with Clinical Efficacy of Evening Primrose Oil in Patients with Atopic Dermatitis (Advances in Therapy, 2014)(accessed: 2026-05-22)
- [5]BookPlants For A Future — Oenothera biennis(accessed: 2026-05-22)
- [1]WikipediaGemeine Nachtkerze (Wikipedia DE)(accessed: 2026-05-22)
- [2]WikipediaOenothera biennis (Wikipedia EN)(accessed: 2026-05-22)