At the moment, there are two drugs which have been making the news.
EPO is short for Epoietin alfa.
It is a drug which increases the amount of red blood cells in your body. These carry oxygen round your body. The more oxygen you have in your body, the easier it is to do exercise.
This is a type of steroid.
It increases the size of your muscles. It is hard to detect, because it can be made in the body naturally.
THG is short for tetrahydrogestrinone, another type of steroid drug.
It improves the body's ability to compete by reducing tiredness and building muscles.