Evening primrose is a plant with yellow flowers. Evening primrose oil comes from the plant's seeds.

People take evening primrose oil as a dietary supplement. It most often comes in capsules to take by mouth. The supplement has omega-6 fatty acids, including gamma-linolenic acid, also called GLA.

People take evening primrose to treat many conditions.

Most research on the use of evening primrose offers little to no help for these conditions:

• Atopic dermatitis, also called eczema.
• Breast pain.
• Diabetic neuropathy, a type of nerve damage that can be caused by diabetes.
• Premenstrual syndrome, also called PMS.

When taken by mouth in typical amounts for a short time, evening primrose oil is most likely safe.

But taking evening primrose oil can cause:

• Upset stomach.
• Loose stools.
• Headache.

Don't take evening primrose if you have a bleeding condition. Taking the supplement may raise the bleeding risk. If you're having surgery, stop taking evening primrose two weeks before the surgery.

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

Evening primrose oil might raise the risk of pregnancy complications. Some types of evening primrose may act like estrogen. So people with hormone-sensitive cancers also shouldn't take it. It also may raise blood pressure.

Possible interactions include:

• Anticoagulants and anti-platelet medicines, herbs and supplements. These types of medicines, herbs and supplements keep blood from clotting. Taking evening primrose while also taking these medicines may raise the risk of bleeding.
• Cytochrome P450 3A4 substrates, also called CYP3A4 substrates. Use evening primrose with care if you take a medicine affected by these enzymes. One such medicine is the cholesterol-lowering lovastatin (Altoprev).
• Lopinavir-ritonavir (Kaletra). This medicine treats the infection caused by human immunodeficiency virus, also called HIV. Evening primrose oil might slow how quickly the body breaks down this medicine.
• Phenothiazines. These medicines treat serious mental health conditions. Taking evening primrose oil with phenothiazines may raise the risk of seizures in some people.