Benefits
Skin moisture in healthy adults (one trial)
In one 12-week placebo-controlled trial in healthy adults (Efamol brand, 3 g/day), skin moisture improved by 12.9%, transepidermal water loss by 7.7% and roughness by 21.7%, and these measures, along with elasticity and firmness, were significantly better than placebo at week 12; redness did not differ, and there was no difference at week 4. It is a single trial by one author and has not been independently repeated. For eczema the answer is no: a 2013 Cochrane review covering 19 EPO trials found it no better than placebo.
Menopausal hot flashes: mixed, weak evidence
Results are mixed. In a 6-month placebo-controlled trial (56 women, 4 g/day), EPO did no better than placebo for hot flushes (Chenoy 1994). A 6-week trial of 1 g/day in 56 women found hot flashes became less severe than on placebo, but their frequency and duration did not differ significantly from placebo (Farzaneh 2013). An 8-week single-blind trial of 2 g/day found no benefit for hot flashes but fewer night sweats (Kazemi 2021). Two meta-analyses disagree on which measure, if any, improves, and a 2024 meta-analysis judged the evidence insufficient to draw firm conclusions. For PMS and cyclical breast pain, controlled trials and meta-analyses found EPO no better than placebo, including a 555-woman trial of the former prescription product Efamast.
Nerve function: small trials in a medical condition
Two placebo-controlled trials in people with diabetic nerve damage (22 patients in 1990 and 111 patients in 1993) reported better nerve-conduction and sensory measures with 360 to 480 mg/day of GLA. Since then, a 4-week trial in 66 patients (2025) reported less nerve pain on 1 to 2 g/day of EPO than on placebo, and a 2020 trial found GLA similar to alpha-lipoic acid, with no placebo-only group. No trial as large or as long as the 1993 study has been done since. This is research in a medical condition that needs a doctor's care, not evidence that EPO protects nerves in healthy people.
Joint stiffness and pain: small, mixed trials
EPO's own trials in rheumatoid arthritis are small and mixed. In a 12-month trial (49 patients across three arms, 540 mg GLA/day from EPO in one arm), patients on EPO reported feeling better and cut back their anti-inflammatory painkillers (NSAIDs), but the authors found no evidence that it changed the disease (Belch 1988). A 40-patient trial of 6 g/day found less morning stiffness at 3 months, while the olive-oil comparison group improved on pain and joint scores at 6 months, and an 18-patient trial of about 20 ml of oil a day found no benefit. A 2011 Cochrane review found that GLA oils as a group relieved some pain, but that pooled result came only from borage and blackcurrant seed oil trials at 1.4 to 2.8 g of GLA a day, several times what a typical EPO dose supplies; none of the EPO trials contributed to it.
Mechanism of action
Delta-6-desaturase bypass and DGLA production
Dietary linoleic acid must be converted to GLA by the enzyme delta-6-desaturase, a slow step. Impaired conversion has been shown in diabetic animals and has been inferred, but not directly established, in people with eczema and diabetes. GLA from EPO skips this step and is converted to DGLA, the precursor of prostaglandin E1. This theory drove decades of eczema research, but placebo-controlled trials in eczema found no clinical benefit.
Prostaglandin E1 and 15-HETrE production
DGLA made from GLA is converted by cyclooxygenase enzymes to prostaglandin E1 and by 15-lipoxygenase to 15-HETrE, which dampen inflammation and platelet clumping in laboratory studies. A small part of DGLA can also become arachidonic acid, the precursor of pro-inflammatory eicosanoids. In people, an anti-inflammatory effect has not been shown convincingly: in one small rheumatoid arthritis trial, plasma prostaglandins moved the same way on EPO as on olive oil, and neither group improved.
Skin lipids and water loss
GLA and its product DGLA are built into skin phospholipids. In one trial in healthy adults, transepidermal water loss was significantly lower after 12 weeks of oral EPO than after placebo (reported as a 7.7% improvement). In eczema, where this effect was expected to matter most, placebo-controlled trials found no clinical benefit.
Clinical trials
Cochrane systematic review and meta-analysis of randomized, placebo-controlled trials of oral evening primrose oil or borage oil for eczema (Bamford et al., Cochrane Database Syst Rev 2013; literature searched to August 2012).
27 randomized trials with 1,596 children and adults with atopic eczema; 19 of the trials tested EPO.
EPO did not improve global eczema symptoms compared with placebo, whether rated by patients (7 trials, 176 participants; mean difference -2.22 on a 0 to 100 scale, 95% CI -10.48 to 6.04) or by doctors (8 trials, 289 participants; mean difference -3.26, 95% CI -6.96 to 0.45). The authors concluded that oral EPO and borage oil are not effective treatments for eczema and that further trials would be hard to justify. Side effects were mild, mainly digestive, and similar to placebo. Separately, the UK had already withdrawn the prescription licences of Epogam (eczema) and Efamast (breast pain) in October 2002, because the evidence did not meet the efficacy standard required of a medicine.
Randomized, double-blind, placebo-controlled trial at seven centres: GLA 480 mg/day vs placebo for 1 year. Outcomes: motor nerve conduction, nerve action potentials, hot and cold thresholds, sensation, tendon reflexes and muscle strength (Keen et al., Diabetes Care 1993).
111 adults with mild diabetic neuropathy, a medical condition; not a general or healthy population. 1-year intervention.
All 16 measures changed more favourably on GLA than on placebo, and 13 of the differences were statistically significant. The benefit was larger in patients whose diabetes was well controlled. An earlier 22-patient trial (Jamal 1990) reported similar results. No trial of this size or length has been done since: a 2025 trial in 66 patients lasted 4 weeks, and a 2020 trial compared GLA with alpha-lipoic acid with no placebo-only group. This is disease research, not evidence for healthy people, and diabetic nerve damage needs medical care.