How often is it appropriate to take evening primrose oil?

Don't know. A problem with anything not prescribed by a dr. Is that we have no idea what is in the substance you are taking.Please read the very small print on the bottle that states "this is not to be used for the treatment or diagnosis of any disease".Why is that statement there?Because the fda, the oversight of drug safety in the usa, hasn't even looked at the product you are taking.Be an informed user.