Sigrid,

Not everyone wants (or cares about) squeaky clean. If your book description mentions that some of the characters are drug addicts, most people can figure out that both language and situations might be rough. People who are looking for lighter or more "pristine" fare probably won't pick up your book at all.

I'm writing about my past experience with cancer. It's not a pretty picture, and I hope no one would expect it to be. Just write the best book you can.