Evening primrose is a plant with yellow flowers.

Evening primrose oil extracted from plant seeds is usually sold in capsules. The supplement contains the fatty acid gamma-linolenic acid (GLA).

People take evening primrose oil orally to treat a wide variety of conditions.

Research on evening primrose use for specific conditions shows:

• Atopic dermatitis (eczema). Research on oral use of evening primrose oil to treat eczema has produced conflicting results. The most comprehensive evaluation is that evening primrose taken orally doesn't effectively relieve the signs and symptoms of eczema.
• Diabetic neuropathy. Research on the use of evening primrose oil to treat this type of nerve damage that can occur if you have diabetes has been inconclusive.
• Premenstrual syndrome (PMS). Research suggests no benefit for oral use of evening primrose oil to treat symptoms of PMS.

When taken in appropriate amounts short term, oral use of evening primrose oil is most likely safe.

Evening primrose oil can cause:

• Upset stomach
• Headache

Don't take evening primrose if you have a bleeding disorder. Oral use of the supplement might increase the risk of bleeding. If you're planning to have surgery, stop taking evening primrose two weeks beforehand.

Also, don't take evening primrose if you have epilepsy or schizophrenia. The supplement might increase your risk of seizures.

Evening primrose oil might increase the risk of pregnancy complications.

Possible interactions include:

• Anticoagulants and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. Combining oral use of evening primrose oil with them might increase the risk of bleeding.
• Cytochrome P450 3A4 (CYP3A4) substrates. Use evening primrose cautiously if you're taking a drug affected by these enzymes, such as lovastatin (Altoprev).
• Lopinavir and ritonavir (Kaletra). This combined medication is used in the treatment of the infection caused by the human immunodeficiency virus (HIV). Evening primrose oil might slow down how quickly this medication is broken down in the body.
• Phenothiazines. Taking evening primrose oil with these drugs used to treat serious mental and emotional disorders might increase risk of seizures in some people.