According to MedLinePlus, there are potential adverse interactions between Metoprolol and Panex ginseng (red ginseng). "Panax ginseng might decrease how quickly the liver breaks down some medications. Taking Panax ginseng along with some medications that are changed by the liver can increase the effects and side effects of your medication." (http://www.nlm.nih.gov/medlineplus/druginfo/natural/1000.html)
I'd highly recommend talking to your doctor if you are still considering taking ginseng.