one way to start off an essay correctly is to state what the problems are about the topic.
the work you way to the positive affects of the drugs.
a second way is to start with a reason as to why you are writing an essay, ((this is correct, but teachers hate it this way))
last is to ask the question back to yourself. "why are drugs good/bad" ---> "drugs are good because they affect the host and enable new possibilities, but drugs are bad because they damage the body and cause sever and possibly fatal problems."