There are few limits; of course, nothing overly-promotional or click bait stuff. In general though, no adult content, no promoting things like firearms, drugs, etc.
There's ways to write about such topics without promoting them that may be acceptable, depending on how you approach it. For example, I wrote about my religion's views on sex, but I didn't write anything explicit, it was more of a theological discussion on sex. So it was deemed acceptable.
Sometimes if they find a topic pushes boundaries they'll disable the ads, but still let you publish it.