Women with PMS have been shown to have impaired conversion of linoleic acid (an essential fatty acid) to gamma linolenic acid (GLA).¹ Because a deficiency of GLA might, in theory, be a factor in PMS and because evening primrose oil (EPO) contains significant amounts of GLA, researchers have studied EPO as a potential way to reduce symptoms of PMS. In several double-blind trials, EPO was found to be beneficial,^2,3,4,5 whereas in other trials it was no more effective than placebo.^6,7

Despite these conflicting results, some doctors consider EPO to be worth a try; the amount usually recommended is 3–4 grams per day. EPO may work best when used over several menstrual cycles and may be more helpful in women with PMS who also experience breast tenderness or fibrocystic breast disease.⁸

In double-blind research, evening primrose oil (EPO) has reduced symptoms of FBD,^9,10 though only slightly.¹¹ One group of researchers reported that EPO normalizes blood levels of fatty acids in women with FBD.¹² However, even these scientists had difficulty linking the improvement in lab tests with an actual reduction in symptoms. Nonetheless, most reports continue to show at least some reduction in symptoms resulting from EPO supplementation.^13,14 Based on this research, many doctors recommend a trial of 3 grams per day of EPO for at least six months to alleviate symptoms of FBD.

Women with PMS have been shown to have impaired conversion of linoleic acid (an essential fatty acid) to gamma linolenic acid (GLA).¹⁵ Because a deficiency of GLA might, in theory, be a factor in PMS and because evening primrose oil (EPO) contains significant amounts of GLA, researchers have studied EPO as a potential way to reduce symptoms of PMS. In several double-blind trials, EPO was found to be beneficial,^16,17,18,19 whereas in other trials it was no more effective than placebo.^20,21

Despite these conflicting results, some doctors consider EPO to be worth a try; the amount usually recommended is 3–4 grams per day. EPO may work best when used over several menstrual cycles and may be more helpful in women with PMS who also experience breast tenderness or fibrocystic breast disease.²²

A preliminary trial found that elderly women with osteoporosis who were given 4 grams of fish oil per day for four months had improved calcium absorption and evidence of new bone formation.²³ Fish oil combined with evening primrose oil (EPO) may confer added benefits. In a controlled trial, women received 6 grams of a combination of EPO and fish oil, or a matching placebo, plus 600 mg of calcium per day for three years.²⁴ The EPO/fish oil group experienced no spinal bone loss in the first 18 months and a significant 3.1% increase in spinal bone mineral density during the last 18 months.

Researchers have reported that people with eczema do not have the normal ability to process fatty acids, which can result in a deficiency of gamma-linolenic acid (GLA).²⁵ GLA is found in evening primrose oil (EPO), borage oil, and black currant seed oil. Some,^26,27,28 but not all,^29,30,31,32 double-blind trials have shown that EPO is useful in the treatment of eczema. An analysis of nine trials reported that the effects for reduced itching were most striking.³³ Much of the research uses 12 pills per day; each pill contains 500 mg of EPO, of which 45 mg is GLA. Smaller amounts have been shown to lack efficacy.³⁴

A preliminary report suggested that evening primrose oil improves blood flow to the legs and heals or reduces the size of venous leg ulcers.³⁵ No controlled research has further investigated this claim.

Oils containing the omega-6 fatty acid gamma linolenic acid (GLA)—borage oil,^36,37,38 black currant seed oil,³⁹ and evening primrose oil (EPO)^40,41—have been reported to be effective in the treatment for people with RA. Although the best effects have been reported with use of borage oil, that may be because more GLA was used in borage oil trials (1.1–2.8 grams per day) compared with trials using black currant seed oil or EPO. The results with EPO have been mixed and confusing, possibly because the placebo used in those trials (olive oil) may have anti-inflammatory activity. In a double-blind trial, positive results were seen when EPO was used in combination with fish oil.⁴² GLA appears to be effective because it is converted in part to prostaglandin E1, a hormone-like substance known to have anti-inflammatory activity.

Though low levels (2 grams per day) of evening primrose oil appear to be without action,⁴³ 3–4 grams per day have lowered cholesterol in double-blind research.⁴⁴ Lowering cholesterol levels should in turn reduce the risk of atherosclerosis.

Preliminary research shows that chondroitin sulfate may prevent atherosclerosis in animals and humans and may also prevent heart attacks in people who already have atherosclerosis.^45,46 However, further research is needed to determine the value of chondroitin sulfate supplements for preventing or treating atherosclerosis.

Caution: One study showed a slightly increased risk of vascular surgery among people with intermittent claudication who took beta-carotene supplements.⁴⁷ Until more is known, people with intermittent claudication wishing to use beta-carotene supplements should first consult with their doctor.

A greater intake of the omega-3 fatty acids found in fish oils has been linked to reduced risk of COPD,⁴⁸ though research has yet to investigate whether fish oil supplements would help people with COPD. In a double-blind trial, people with COPD received a fatty acid supplement (providing daily 760 mg of GLA [gamma-linolenic acid], 1,200 mg of ALA [alpha-linolenic acid], 700 mg of EPA [eicosapentaenoic acid], and 340 mg of DHA [docosahexaenoic acid]) or a placebo (80% palm oil and 20% sunflower oil) during an eight-week rehabilitation program. Compared with the placebo, the fatty acid supplement significantly improved exercise capacity.⁴⁹ While two of the fatty acids supplied in this supplement (EPA and DHA acid) are found in fish oil, it is not known which components of the supplement were most responsible for the improvement. Gamma-linolenic acid is found in evening primrose oil, black currant seed oil, and borage oil; alpha-linolenic acid is found in flaxseed oil and other oils.

Fatty acids in evening primrose oil (EPO) inhibit the formation of biochemical messengers (prostaglandins) that promote blood vessel constriction. A double-blind trial of 21 people with Raynaud’s disease found that, compared with placebo, supplementation with EPO reduced the number and severity of attacks despite the fact that blood flow did not appear to increase.⁵⁰ Researchers have used 3,000–6,000 mg of EPO per day.

A deficiency of several essential fatty acids has been observed in some children with ADHD compared with unaffected children.^59,60 One study gave children with ADHD evening primrose oil supplements in an attempt to correct the problem.⁶¹ Although a degree of benefit was seen, results were not pronounced. In a 12-week double-blind study, children with ADHD were given either a placebo or a fatty-acid supplement providing daily: 186 mg of eicosapentaenoic acid (EPA), 480 mg of docosahexaenoic acid (DHA), 96 mg of gamma-linolenic acid (GLA), 864 mg of linoleic acid, and 42 mg of arachidonic acid. Compared with the placebo, the fatty-acid supplement produced significant improvements in both cognitive function and behavioral problems.⁶² No adverse effects were seen. In a preliminary trial, supplementation with approximately 400 mg of flaxseed oil and 25 mg of vitamin C, each twice a day for three months, was associated with an improvement of symptoms in children with ADHD.⁶³

In one trial, women with IBS who experienced worsening symptoms before and during their menstrual period were helped by taking enough evening primrose oil (EPO) to provide 360–400 mg of gamma linolenic acid (GLA) per day.⁶⁴ In that trial more than half reported improvement with EPO, but none was helped in the placebo group. The effects of EPO in other groups of IBS sufferers have not been explored.