Is it illegal to buy medicine if you live in the usa from overseas?

I am looking to buy my medication from overseas, since its a fraction of the cost, but I am confused if its illegal? The drug I need is not a narcotic/pain reliever. Is it illegal to have some one mail me my medication? I would not be buying it through a web site but a family member would purchase it for me and send it by mail. I do have a valid prescription. Thank you.