Gamma-linolenic acid (GLA) is an omega-6 fatty acid found in certain plant oils, such as evening primrose oil, borage oil, and blackcurrant seed oil. Its use in the support and treatment of premenstrual syndrome (PMS) is primarily based on the hypothesis that women with PMS may have impaired conversion of linoleic acid to GLA, leading to altered prostaglandin synthesis and worsening symptoms. This biological rationale has led to the investigation of GLA supplementation as a possible therapy for PMS, aiming to improve symptoms like breast tenderness, mood swings, and bloating.

Several small clinical trials and reviews have evaluated GLA (primarily from evening primrose oil) for PMS. Some early studies reported modest benefits in reducing symptoms, but these studies often suffered from methodological limitations such as small sample sizes, lack of proper blinding, or inconsistent outcome measures. More recent and better-controlled trials have generally failed to demonstrate a clinically significant benefit of GLA over placebo. Systematic reviews and meta-analyses (e.g., Cochrane reviews) have concluded that there is insufficient and inconsistent evidence to support the efficacy of GLA for PMS.

In summary, while the use of GLA for PMS has a plausible biological rationale and modest historical support, the current scientific evidence is weak and inconsistent. As such, GLA is sometimes used, but its effectiveness for PMS is not strongly established by rigorous scientific studies.