This combination is a complex one. Citalopram, as an SSRI, is often taken in combination with gabapentin (Neurontin), and atenolol. However, oxycodone (and Ambien) possess abuse potential, and should be discussed specifically and carefully with your prescribing physician.
If you think you or someone you know has taken too much atenelol, call your poison control center immediately or take them to the emergency room.
It's bad to drink alcohol with medication, or any type of drug for that matter. Certain chemicals don't mix.
With any drug you should always use precaution when mixing for the first time. Atenelol and Ativan can interact but it is highly unlikely. I am currently prescribed both and have not encountered a problem.