When you brainstorm about this topic, you may wish to examine how some over the counter medications in recent times have become non-over the counter now. Specifically, consider how pseudoephedrine [Sudafed] has been removed from the counters because it is used in the production of crystal-methamphetamine. And, recently on the news, a young man died from mixing cough medicine with something else....
The problem, of course, is that irresponsible people purchase these drugs. How far, then, must the government police people?
Any issue which has at least two sides is generally an acceptable topic for persuasive writing. In this case, the topic is quite relevant and important for today, making it just the kind of thing to research and write about at the AP level. Interesting idea!
The topic you describe can definitely be used as the topic for a persuasive essay in any high school class at any level. The important thing in writing a persuasive essay is to make sure that you spend time in advance brainstorming ideas both for and against the topic. Before you start writing your rough draft, make sure you have taken a stand one way or the other. The most common error I see in high school persuasive compositions is that the writer does not take one side or the other.