Blood doping is know as an illicit because it improves performance by synthetically boosting the blood's ability to bring more oxygen to the working muscles. Sports performers chose to inject themselves with blood doping because blood doping increases the amount of haemoglobin in the bloodstream; haemoglobin is an oxygen carrying protein in the blood. So, by increasing haemoglobin in the bloodstream it allows higher amounts of oxygen to reach and fuel a sports performer's muscles, this then improves the performers stamina and performance, particularly in long distance events, such as athletics and cycling. The side effects that can occur after using this drug is it can increase blood viscosity which can lead the blood becoming really thick,
