Onagraceae
Oenothera biennis
Evening primrose
- Part used
- seedoil
- Native range
- Eastern North America; naturalised widely across Europe and elsewhere
- Morphology
- A biennial to two metres forming a rosette in the first year, then a tall spike of large yellow four-petalled flowers that open at dusk within minutes, visibly, and are pollinated by moths.
What is in it
Evidence
One of the most decisive negative results in this collection. A Cochrane review of evening primrose oil for eczema found no benefit and concluded further trials were not justified. UK licences for eczema products were withdrawn in 2002 when the regulator found the evidence did not support them. Premenstrual and menopausal claims are similarly unsupported.
Safety
Generally well tolerated; gastrointestinal upset and headache are commonest. Case reports associate it with lowered seizure threshold, and caution is advised in epilepsy. Antiplatelet activity at higher doses.
Interactions: Additive with anticoagulants; May lower seizure threshold; caution with anticonvulsants
Regulatory: Permitted as a listed ingredient. UK product licences for eczema were withdrawn in 2002.
Historical use
Used by Cherokee and other eastern peoples as food and for skin complaints. Its modern use dates entirely from the 1980s, when gamma-linolenic acid was proposed as a treatment for eczema and premenstrual syndrome.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
Evening primrose oil is the clearest case here of a product surviving the withdrawal of its own licence.
It was licensed in the United Kingdom as a medicine for eczema. In 2002 the regulator reviewed the accumulated evidence, concluded it did not support the indication, and withdrew the licences. Cochrane's later review was blunter still: no benefit, and no case for further trials.
It remains one of the best-selling supplements in the English-speaking world, sold for the same conditions, because losing a medicine licence does not prevent something being sold as a supplement. The regulatory categories are separate, and a product that has failed as a medicine simply moves across.
The flowers are worth watching regardless. They open at dusk over a minute or two, fast enough to see it happen.
Nomenclature verified against GBIF backbone taxonomy.