Most people can use evening primrose oil without complications. But keep in mind that there have been reports of side effects such as:
Evening primrose oil may raise the risk of bleeding among people who take anticoagulant and antiplatelet medications. It may also raise the risk of seizures as well as serious nausea and vomiting for people taking a class of drugs known as phenothiazines. These drugs are used to treat schizophrenia and other psychotic disorders.
Headache
Stomach upset
Nausea
Dizziness
Rash