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Application of Oenothera species
Scientific Name: Evening Primrose
Other Names: Fever Plant, OEP, Oenothera species, Sun Drop
Who is this for?
Oil pressed from the seeds of evening primrose plants contains large amounts of polyunsaturated omega-6 fatty acids. These are among the essential fatty acids (EFAs) needed by the body to regulate activities such as heart function, insulin utilization, and mood balance. The body cannot produce EFAs, so they must be eaten in the diet or taken as supplements. Estimates are that between 65% and 80% of evening primrose oil is composed of the EFA linoleic acid and between 2% and 15% is another EFA, gamma-linolenic acid (GLA). Linoleic acid may play a role in the ways that the body utilizes insulin, maintains weight, and resists cancer and heart disease. Linoleic acid is converted into GLA when it is digested in the body. GLA is believed to interrupt the body's production of chemicals that initiate and maintain inflammation. Therefore, evening primrose oil is often used to treat inflammatory conditions such as rheumatoid arthritis (RA) and asthma. In multiple animal and human studies, taking evening primrose oil reduced inflammation, joint damage, and pain from RA. However, relief took up to 6 months to reach full effectiveness for some individual study participants. Results from other studies were inconclusive, with many finding little or no effectiveness for evening primrose oil in asthma and other inflammatory conditions. Some very early findings from other studies suggest that evening primrose oil may be useful in treating chronic fatigue syndrome, but more research is needed before evening primrose oil can be recommended for that condition.
In animal studies, oral doses of evening primrose oil have shown some promise for the treatment of high blood pressure, heart diseases, and high cholesterol. In animal studies of linoleic acid and in both animal and human studies of GLA supplementation, general decreases in blood pressure were seen. Evening primrose oil has been shown to reduce the clumping of blood components called platelets. As a result, atherosclerosis (hardening of the arteries) may be delayed or prevented. Results for the cholesterol studies are not as clear in some studies, only triglycerides were reduced while other studies showed overall reductions in cholesterol. It is believed that several processes, including the possible relaxation of blood vessel walls, are involved in the potential use of evening primrose oil for these conditions. More studies are needed, though, before evening primrose oil can be recommended for preventing heart diseases or high cholesterol.
Chemicals called isoflavones, which belong to a larger class of plant chemicals known as phyto (plant-derived) estrogens, are contained in evening primrose oil. Because isoflavones are similar in shape to the female hormone, estrogen, they may attach to estrogen receptors potentially displacing some of the natural estrogens in a womans body. Therefore, isoflavones may possibly prevent or relieve estrogen-related symptoms, such as breast pain, that are associated with premenstrual syndrome (PMS). Additionally, women who have PMS may also have a decreased ability to convert linoleic acid into GLA. Some evidence shows that symptoms of PMS and menopause may be worsened by deficiencies of EFAs. Therefore, both its isoflavones and its EFAs may give evening primrose oil some ability to relieve PMS, as well as symptoms of menopause. Because it may induce contractions of the uterus, evening primrose oil has been used by midwives to start labor for pregnant women. However, no reliable studies support this use of evening primrose oil, prescription medications are more effective, and labor should only be initiated by a healthcare professional who is familiar with the procedure.
Both oral and topical forms of evening primrose oil have also been studied for treating acne, eczema, psoriasis, and other skin conditions. Although its effectiveness has not been proven, evening primrose oil continues to be studied for these uses. When it is applied to the skin, evening primrose oil has moisturizing and softening effects, so it is often included in cosmetics such as face cream.
When should I be careful taking it?
Evening primrose oil has been used by midwives to start labor or to shorten the length of time that women are in labor during the delivery of a baby. If it is taken during pregnancy, it may increase the risk of miscarriage or complications; therefore, evening primrose oil should not be taken during pregnancy and only a health professional should use it to start labor.
It is thought that taking evening primrose oil may lower the seizure threshold meaning that it may make individuals with epilepsy more likely to have seizures. Therefore, individuals who take medications to prevent seizures and individuals who have ever had a seizure should avoid taking evening primrose oil.
What side effects should I watch for?
Taking evening primrose oil may result in bloating, indigestion, or soft stools. Some individuals have also reported headaches from taking it. If large doses of evening primrose oil are ingested, oil may leak from the gastrointestinal tract.
What interactions should I watch for?
In studies and case reports, GLA has been shown to increase the time blood needs to clot. Due to the high percentage of GLA in evening primrose oil, blood-thinning effects may be increased if evening primrose oil is taken at the same time as an antiplatelet or anticoagulant drug, possibly resulting in uncontrolled bleeding.
Reportedly, seizures have been attributed to taking evening primrose oil at the same time as some drugs for treating schizophrenia. Avoid using evening primrose oil while taking drugs such as:
Although no cases have been reported in scientific literature, it is possible that evening primrose oil may interfere with the effects of medications to treat epilepsy. Avoiding oral evening primrose oil is recommended for individuals who take anti-epileptic drugs that include:
The GLA in evening primrose oil may affect the ability of blood to clot after an injury. Aspirin can also delay clotting, so evening primrose oil should not be taken orally at the same time as aspirin.
Some non-prescription products such as dexchlorpheniramine (an antihistamine) and pseudoephedrine (a decongestant) possibly may make seizures more likely to recur. Although the risk is thought to be slight, taking evening primrose oil may also increase the possibility of seizures for individuals who have had seizures previously, so taking evening primrose oil at the same time as non-prescription antihistamines or decongestants is not recommended.
Theoretically, if evening primrose oil is used with other herbs that affect blood clotting, bleeding may occur. Some of the most common herbal products that might inhibit blood clotting are:
Evening primrose oil may "lower the seizure threshold", which means it may make seizures more likely to recur in individuals who have had previous seizures. When evening primrose oil is taken with other herbal products that may also induce seizures, this risk increases. Some other herbals that may lower the seizure threshold include:
Some interactions between herbal products and medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals.
Should I take it?
Evening primrose is actually a weed. Originating in North America, it has spread to Europe and most other mild climate areas of the world, but it is cultivated mainly in Canada and the United States. Evening primrose plants may reach 3 to 8 feet tall. They are biennial, which means they take 2 years to reach maturity. During the first year, only a "rosette" or a cluster of large dark green leaves forms close to the ground. In the second spring, stems develop and the plant flowers. Evening primrose gets its name from the bright yellow rose-like flowers it produces. Blooming throughout the summer months, the flowers of evening primrose each last only one day opening as the sun goes down, remaining open to attract insects that are active during the night, and then dying away in sunlight. Seed pods that are about 2 inches long contain large numbers of small seeds that are harvested and pressed to produce the oil that is used in medicines and cosmetics.
Recently, prescription-only forms of evening primrose oil that were available in the United Kingdom but not in the United States were withdrawn from the market. While they are considered safe to use, their effectiveness is questionable. Non-prescription dietary supplements containing evening primrose oil are still sold in the U.K. even though studies have failed to prove them effective.
Dosage and Administration
Although it may be available as a liquid oil, evening primrose oil is most commonly taken in soft gelatin capsules. Different brands contain varying amounts of the oil and directions for use also vary. If you decide to use an evening primrose product, the instructions on the package should be carefully followed.
Some general daily dose ranges used in human studies are:
For topical use, evening primrose oil may be applied as often as needed.
Evening primrose oil supplies significant amounts of essential fatty acids notably linoleic acid and gamma linolenic acid, which may block inflammation. Rheumatoid arthritis, asthma, and other inflammatory diseases may be relieved by taking evening primrose oil. Because deficiencies of essential fatty acids are associated with symptoms of pre-menstrual syndrome and menopause, it is believed that evening primrose oil supplementation may help to relieve these conditions. Evening primrose oil is also used to treat skin conditions such as acne and psoriasis.
Because evening primrose oil may cause labor to start, it should not be taken by women who are pregnant. Individuals with epilepsy should also avoid evening primrose oil because it may make seizures more likely to occur.
Most side effects from taking evening primrose oil by mouth are mild. They may include headaches, indigestion, and soft stools.
Oral evening primrose oil may increase the blood-thinning effects of drug or herbal anticoagulants or antiplatelet agents. It may increase the risk of seizures when taken with certain prescription drugs for schizophrenia, non-prescription cough and cold products, or herbals. It may also interfere with anti-epileptic drugs.
Last Revised August 4, 2004
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(Note: The above information is not intended to replace the advice of your physician, pharmacist, or other healthcare professional. It is not meant to indicate that the use of the product is safe, appropriate, or effective for you.)