It's your book so you can include whatever you like. There's no hard and fast rule that a work of young adult fiction cannot contain references to things such as drinking, drugs or sex; however, if you're familiar with the genre, you'd be in a position to know the general parameters for what's deemed acceptable, so if you're not sure what they might be, it would be a good idea to read as much as possible. Essentially, how far into the corners of the framework any given author might be able to get without being told to make major alterations to the finished product would depend on three things: #1) the agent's and/or publisher's confidence that the risque content isn't out of place and fits in with the rest of the story, thereby making it difficult or impossible to excise or change. #2) the agent's and/or publisher's confidence that the work itself is a solid piece of writing that has the potential to receive critical acclaim or to achieve some level of commercial success, in which case it's likely that anything blue will simply be overlooked or overshadowed by other things. Or, #3) the fact that the author has a track record of producing material that's generally well-received and can therefore throw his or her weight around a bit when shopping new material.
So, my advice would be to go out and read a number of young adult works of fiction. Let's say you manage to read ten novels in the next three months. Then you'll be in a position to measure how often drinking, drugs and sex were mentioned in those ten books combined and gauge whether or not your book exceeds the average.
You can also take pains to ensure that what you're including is necessary and relevant to the story. I'm not sure what your first-hand experience with drinking, drugs and sex might be and I'm certainly not going to advise you to drink, take drugs and have sex in order to write your book. But anyone who has been drinking before, taken drugs or had sex will know immediately if you don't know what you're on about if you include those things in your book and fail to present them realistically. A passing mention of drinking, drugs or sex would likely go under the radar, but spending a sizable chunk of time going into one or all of those topics would likely raise eyebrows for anybody who's looking to engage in some young adult content.