Google has published content guidelines for its AdWords program to indicate what ads will get accepted or rejected.

Google bans ads promoting spam services, miracles cures, alcohol and sexual content. These policies provide Google advertisers what is acceptable or not.

"Google is committed to providing an advertising service with fair and consistent policies that benefit our users, advertisers, partners, and Google. To achieve this goal, we maintain high standards for ads accepted into the AdWords program. The policies listed below complement our Terms and Conditions and describe Google's advertising policies with regards to products and services," Google states on its Web site.

Additional resources:

Google AdWords Content Policy