You can also mention the side effects drugs have on the body, such as:
Skeletal abnormalities, joint and muscle problems,diabetes, heart disease, aggression,nausea,dehydration,headaches and possible death.
thats just a few examples,
You can mention that having Drug testing in sport can minimise the risk as drug testing can act as a detterent to some athletes that are thinking about taking drugs.
oh well... hope it helps..