GLA (gamma-linolenic acid) is an omega-6 fatty acid sold as a supplement, most commonly in the form of evening primrose oil or borage oil. It’s marketed for skin conditions, joint inflammation, and hormonal balance. Your body can make GLA on its own from linoleic acid (a fat found in many cooking oils), but certain health conditions and aging can slow that conversion, which is the basic rationale behind supplementation.
What GLA Is and Where It Comes From
GLA is a polyunsaturated fatty acid in the omega-6 family. Despite sharing the omega-6 label with fats often associated with inflammation, GLA behaves differently in the body. It’s found naturally in a handful of plant seed oils. Borage oil is the richest source, containing 20 to 23% GLA by weight. Evening primrose oil, the more popular supplement form, contains about 8 to 10%. Black currant seed oil falls somewhere in between.
Most GLA supplements come as soft gel capsules of one of these oils. Because borage oil is more concentrated, you need fewer capsules to reach the same dose compared to evening primrose oil. The typical supplemental range is 320 to 480 mg of GLA per day, and doses up to 2.8 grams daily have been used for up to a year without major safety concerns.
How GLA Works in the Body
Once you swallow a GLA supplement, your body converts it into a compound called DGLA. From there, DGLA can follow several paths. The one that interests researchers most involves an enzyme that turns DGLA into a type of prostaglandin (PGE1) with anti-inflammatory effects. A second pathway produces another anti-inflammatory compound called 15-OH-DGLA.
There is a catch. DGLA can also convert into arachidonic acid, which fuels inflammation rather than calming it. This is why the balance matters, and why simply loading up on GLA doesn’t guarantee a purely anti-inflammatory outcome. Interestingly, skin cells lack the enzyme needed to push DGLA toward arachidonic acid, which is part of why GLA has attracted so much attention for skin conditions specifically.
Why Some People May Be Low in GLA
Your body normally produces GLA from linoleic acid using an enzyme called delta-6 desaturase. This enzyme handles the rate-limiting first step in the conversion process. Several factors can slow it down: aging, diabetes, high alcohol intake, and certain nutritional deficiencies (particularly zinc and magnesium). When this enzyme underperforms, linoleic acid builds up without being converted, and your tissues end up with less GLA and DGLA than they need.
People with atopic dermatitis (eczema) tend to have higher blood levels of linoleic acid and lower levels of GLA and DGLA compared to people without the condition. This pattern suggests their conversion enzyme isn’t working efficiently. The severity of their eczema correlates with the size of that gap, which led researchers to hypothesize that supplementing GLA directly could bypass the bottleneck and improve symptoms.
The Evidence for Skin Conditions
The logic behind GLA for eczema sounds compelling: people with eczema appear to have impaired GLA production, their skin barrier function suffers as a result, and supplementing GLA should theoretically restore what’s missing. The problem is that clinical trials haven’t backed this up.
A Cochrane systematic review, the gold standard for evaluating medical evidence, found no meaningful benefit from either evening primrose oil or borage oil for eczema. A meta-analysis of seven evening primrose oil studies showed no significant improvement in global eczema symptoms compared to placebo. Borage oil fared no better. Improvements that did occur in the supplement groups were matched by similar improvements in the placebo groups. Both the supplements and placebos produced only mild, temporary side effects, mostly digestive.
This doesn’t mean GLA has zero effect on skin biology. It means that in controlled trials, any effect was too small to distinguish from placebo. If you’ve seen anecdotal reports of GLA clearing up someone’s skin, keep in mind that eczema naturally waxes and wanes, and placebo response rates in skin studies tend to be high.
The Evidence for Joint Inflammation
GLA supplementation has shown more promising (though still limited) results for rheumatoid arthritis. Clinical studies have found that GLA treatment is associated with improvements in morning stiffness duration, joint pain and swelling, and the ability to reduce other medications. However, the research base has significant inconsistencies. Studies vary in duration, GLA dose, placebo design, and evaluation criteria, making it difficult to draw firm conclusions about how well it works or what dose is optimal.
The anti-inflammatory pathway from GLA to DGLA to PGE1 provides a plausible biological explanation for these effects. But “plausible mechanism plus mixed results” is a common pattern in supplement research, and it means the jury is still out.
Side Effects and Safety Concerns
GLA supplements are generally well tolerated. The most common side effects are mild digestive issues: upset stomach, loose stools, and occasional headaches. These tend to be temporary.
There are a few important exceptions. If you have epilepsy or schizophrenia, evening primrose oil may lower your seizure threshold. The same risk applies if you take phenothiazine medications for serious mental health conditions. GLA supplements can also interact with blood thinners and anti-platelet medications by increasing the risk of bleeding, so combining them is not recommended without medical guidance.
One additional note for long-term use: there are warnings that taking evening primrose oil for more than a year may carry a potential risk of inflammation, blood clotting issues, and immune suppression due to gradual accumulation in tissues. This is worth considering if you’re planning open-ended supplementation.
Choosing Between Supplement Forms
The three main GLA supplement options are evening primrose oil, borage oil, and black currant seed oil. The practical differences come down to concentration and cost:
- Borage oil delivers the most GLA per capsule (20 to 23% of the oil), so you need fewer pills to hit a target dose.
- Evening primrose oil is the most studied form (8 to 10% GLA), meaning most safety and efficacy data comes from trials using it.
- Black currant seed oil provides a mix of both omega-6 GLA and omega-3 fatty acids, which some people prefer for that reason.
If you’re trying to match doses used in clinical research, check the supplement facts panel for actual GLA content per capsule rather than total oil content. A 1,000 mg evening primrose oil capsule contains roughly 80 to 100 mg of GLA, so you’d need several capsules daily to reach the 320 to 480 mg range commonly studied. A borage oil capsule of the same size would deliver roughly double that amount of GLA.