You're almost there! You have your topic and position that recreational drugs are worse than performance enhancing drugs, and now all you have to do is state "why" in your thesis.
Recreational drugs are worse than performing enhancing drugs because . . .
Finish the thesis with the reasons why. You can list the reasons why or come up with a more general statement as to why they are worse.
Recreational drugs are worse than performance enhancing drugs because of A, B, and C or . . . because of X.
For example, if you were writing an essay on The Adventures of Huckleberry Finn, you might write,
The Adventures of Huckleberry Finn is a great novel because of its characterization, plot, and symbolism.
The Adventures of Huckleberry Finn is a great novel because of Twain's use of literary devices to portray a thematic message.
"Literary devices" is a general statement that tells the reader what you are going to write about. Your reader will know that you are going to discuss some literary devices like characterization, plot, and symbolism in your body paragraphs without listing them in your thesis.
In your case, you might argue that because recreational drugs are statistically used in more dangerous, less sanitary environments, they tend to be more dangerous than performance enhancing drugs. It will be important to find research and statistics to back up your claims—and to recognize the dangers that both kinds of drugs present to the human body.