What drugs do they test for pre-employment?

Each company can have different drugs they test for in a pre-employment screening. Especially with the decriminalization of marijuana in some states, that might make an employer skip that test. Similarly, because alcohol is legal and moderate use is very widespread, they might not care about that during a pre-employment test.

Now, being drunk on the job is totally different, and they may test for that if there's a concern, but having a glass of wine with dinner, in most situations, isn't going to prevent you from getting a new job.

You should note that some medications can create a positive drug test when you haven't been using any illegal substances. The hiring manager or a medical review officer should go through your drug test results and medications to see if this may be the situation.

That doesn't necessarily mean that you're "clear" for the job, but there is usually some leeway and understanding if you're on something like a pain medication that can create a positive result.