Korean doctor Peter Yoon says he has not seen any severe toxic side effects with Somatomdin C. Dr. Yoon says that if too much velvet deer antler (Somatomedin C) is taken, mild upset stomach may occur, which disappears if use of the product is stopped. According to Dr. Koltun, people with circulation problems, congenital heart disease or angina (heart pain) should not take velvet deer antler.