The oil of oenothera biennis, the common evening primrose, is used medicinally to help treat a wide variety of ailments, earning the plant the historical name King’s cure-all. This herb is also called evening star, evening plant, fever plant and field primrose. The oil is used to treat the discomfort associated with premenstrual syndrome and premenstrual stress, breast ailments, migraines, asthma, eczema, inflammation, high cholesterol levels, heart disease, rheumatoid arthritis, diabetes and multiple sclerosis. A warm poultice made from oenothera biennis helps heal bruises, and Native Americans traditionally made a tea from the root for bowel discomfort. The plant’s shoots and roots have also been used as a food source.
The plant is classified as a biennial herb, and it can grow as tall as 6 feet (1.82 meters), but some individual plants reach just 2 feet (0.60 meters). The evening primrose’s 2-inch (5.08-centimeter) flowers are usually yellow and fragrant, with some people comparing the scent to lemons. The flowers bloom at night and remain open in the morning, and each flower’s four petals close up by the afternoon. Oenothera biennis does well in part shade to full sun, and it attracts hummingbirds. Other types of birds are drawn to the seeds, moths are drawn to the flowers, and the leaves and roots provide food for small mammals.
Evening primrose oil, made from oenothera biennis, is commonly available as a capsule or in oil form. The oil is a rich source of a fatty acid called gamma-linolenic acid, which the body converts to a substance that prompts blood vessel contraction. Some people benefit from this herb because their bodies do not have enough gamma-linolenic acid (GLA). A depletion of GLA can be caused by thyroid problems, radiation or alcohol. People who use evening primrose oil should combine it with food to maximize the rate of absorption. The oil’s anti-inflammatory properties are what helps such conditions as menstrual cramps, bloating and joint pain.
Some people experience minor side effects when taking oenothera biennis. These side effects include nausea, loose stools, stomach discomfort and headaches. Pregnant women should not use this herb because uterine contractions may result. These contractions are one reason oenothera biennis is said to help move labor along, although this has not been scientifically proven. Use of evening primrose for this purpose must be timed carefully, with pregnant women advised to refrain from taking it before their pregnancies have reached 34 weeks.