Evening Primrose Oil

Evening primrose is a member of the fuchsia and willow herb family. The common name of the plant is derived from the flower, which opens and releases its scent during the evening. The seeds contain oils that are used therapeutically.

Uses and Benefits:

Evening primrose oil (EPO), along with borage and black currant oils, are rich sources of gamma-linolenic acid (GLA). These plant oils are used for premenstrual syndrome and associated breast pain, eczema, and arthritis. EPO has also been recommended for diabetic peripheral neuropathy, chronic fatigue syndrome, hyperlipidemia, inflammatory bowel disease, schizophrenia, menopausal hot flushes, and many other ailments.Patients with these disorders are thought to be unable to sufficiently convert their dietary essential fatty acids to GLA, a precursor of anti-inflammatory eicosanoids ; thus, supplementation with GLA-rich plant oils is considered beneficial.

Pharmacology:

The key constituents of the seeds are fixed oils containing essential omega-6 fatty acids such as linoleic acid (LA), and especially its derivative gamma-linolenic acid (GLA). EPO contains 7-10% GLA, while borage seed oil contains 23%, and black currant oil contains 15-20%.

The metabolic pathway of GLA is well established in humans and other animals. Dietary linoleic acid, an essential fatty acid, is converted to GLA by a rate-limiting enzymatic step. GLA is then rapidly converted to dihomo-gammalinolenic acid (DGLA), which

GLA supplementation has been shown to attenuate the in vitro response by enriching cells with DGLA, the immediate prcursor of PGE1, without increasing corresponding amounts of AA. DGLA or another metabolite, 15-hydroxy-DGLA, appear to inhibit the AA pathway to its inflammatory byproducts, further in inflammation, and have direct immune modulating effects onT -lymphocytes. A variety of anti-inflammatory effects from GLA supplementation have been demonstrated.

Based on an increase in anti-inflammatory eicosanoids that ,effect platelet function, GLA should be expected to reduce latelet aggregation. Controlled studies in humans have reported varying results, however, with most studies reporting an increase or no change in aggregation. 1 Bleeding time data has not been evalluated.

Clinical Trials:

Numerous clinical trials have evaluated the use of EPO. Problems with several studies include inadequate conlrols (some used olive oil or other potentially active substances as the placebo) and trials that did not run long enough (based on some studies, it may take many months to ameliorate disease).

Atopic Dermatitis/Eczema-Dozens of trials have evaluated EPO for the treatment of eczema and related skin disorders. 2 ,1,g An early meta-analysis of nine mostly small trials that were ran­domized, double-blind, and placebo-controlled found a modest but significant benefit of EPO for the treatment of eczema in a total of 311 patients taking 2-6 g/day (160-480 mg/day GLA) for several months. Lmprovement was found in itching, scaling, in­flammation, dryness, and erythema.

Diabetic Peripheral Neuropathy-Positive animal and human experimental data initiated the clinical study of EPO for peripheral nerve damage related to diabetes. In one high-quality, double­blind RCT in diabetic patients, 6 g/day EPO (480 mg/day

Adverse Effects:

EPO and other GLA-containing plant oils are well tolerated in clinical trials lasting up to 1 year. A few cases of diarrhea or soft stools, belching, abdominal bloating, and headache have been reported.

Side Effects and Interactions:

There are no documented drug interactions.

Cautions:

In early studies of chronic schizophrenia, EPO was reported to worsen the psychosis of three patients, who on electroencephalography evaluation were subsequently found to have temporal lobe epilepsy.Based on this single report, EPO has since been considered to be able to "lower the seizure threshold" in patients with epilepsy. This effect has not been corroborated. There has been one additional report of seizures in a patient taking a combination herbal regimen that included EPO, black cohosh, and chaste tree. Although a cause-and-effect relationship is unlikely, caution is nonetheless warranted in patients with seizure disorders. There are no data on the use of EPO during pregnancy or lactation.

Preparations & Doses:

EPO contains about 8-9% GLA. Almost all the clinical trials have used brands such as Efamol, Epogam, and Efamast.Efamol (available in the U.S.) contains 500 mg of oil and 45 mg of GLA/capsule; Epogram (available in Europe) contains 40 mg GLA. Some products contain a combination of EPO with eicosapentanoic acid, also found in fish oils. The typical dosage of EPO used in most clinical trials is 6 g/day (12 capsules containing about 480-560 mg GLA) in adults, and half that dose in children, in divided doses. For some indications (e.g., cyclical mastalgia) 2-4 g/day of EPO has been used. Because these doses require large numbers of capsules, many patients cannot tolerate this amount or prefer using borage oil or black currant oil, which contain higher concentrations of GLA.

Summary Evaluation

EPa is a well-tolerated source of GLA, an omega-6 fatty acid that has shown promise in many experimental studies and has been used for a variety of clinical disorders. Positive results from well­designed controlled clinical trials have been documented for dia­betic peripheral neuropathy, rheumatoid arthritis, and eczema; however, efficacy is not well established due to mixed or limited trial results. Practical drawbacks to the use of EPa are the large number of capsules required daily, and the onset of action that may take many months.