Gamma-Linolenic acid (GLA) is an Ω-6 essential fatty acid found primarily in vegetable oils.

Chemically, Gamma-Linolenic acid is a carboxylic acid with an 18-carbon chain and three cis double bonds; the first double bond is located at the sixth carbon from the Ω end. It is also sometimes called gamolenic acid and is an isomer of alpha-linolenic acid, which is the Ω-3 fatty acid found in flax seed.

Gamma-Linolenic acid is sometimes prescribed in the belief that it has anti-inflammatory properties lacking some of the common side effects of other anti-inflammatory drugs. Herbal medicine advocates recommend Gamma-Linolenic acid for autoimmune disorders, arthritis, eczema and PMS with noticeable results not expected for months. Research is ongoing, investigating Gamma-Linolenic acid as a potential anticancer agent. Gamma-Linolenic acid is unique among the Ω-6 polyunsaturated fatty acids (linoleic acid, GLA and Arachidonic acid) in its potential to suppress tumor growth and metastasis.

Gamma-Linolenic acid can also form a lithium salt, increasing its solubility in water. The resulting compound is Li-GLA, also called lithium gammalinolenate. Li-GLA is currently in phase II clinical trials to determine whether it is useful in the treatment of HIV infections, since it has the ability to destroy HIV-infected T cells in vitro. It has a number of side-effects, including a reduction in hemoglobin, hematuria, gastrointestinal disturbance, fatigue and headache.