Inception is a tricky movie when it comes to violence. A lot of people are killed: Cobb and Eames are basically running around shooting them like fish in a barrel. The thing is, though, they're not real people; they're just projections.
In fact, there is very little real violence even within the dream world. A few characters are shot (and feel pain) while dreaming, but only once do we see blood and it isn't very much.
However, it's worth noting that Inception doesn't have to be covered in gore to be intense. There are two stabbings (although we see neither) and a real and dream suicide (neither of which we see the conclusion of).
It may be PG-13, but that doesn't mean it won't make you jump. Oh, and as far as sex and drugs and everything else goes, unless you think dream sharing is a gateway to more hardcore intravenous substances, we don't think there's too much to worry about.