Of course, every toxin has a dosage, and just as a small amount of poison will not necessarily hurt you, the more you eat or drink, the higher the risk. Because blood is high in iron and the body has trouble excreting extra iron, any animal that takes blood on a regular basis is at danger of iron overload. The main problem with iron is that it is very reactive - it likes to bind to other molecules. For this reason, eating meat can be dangerous because most of the iron in the food is in the form of heme (a red pigment made up of carbon, hydrogen, and oxygen), which can cause problems for people who are anemic or have other issues with their blood. As for drinking blood, the only real danger is infection. Blood contains many things that bacteria love, so if you donate blood, you should follow strict guidelines to prevent infections. In conclusion, eating blood is not recommended because the iron in your body can end up in other parts of your body where it can do harm. Drinking blood is not recommended because it's a common way to get infected with diseases.