AD means antidepressant. A benzo is short for benzodiazepine, reffering to a class of drugs which has anxyolitic (works against anxiety), muscle relaxant and depressant action (meaning it slows down CNS (brain) activity. If one overdoses on an SSRI (which increases activity in certain areas) one can get what is called serotonin syndome. Among other things it's raises body temperature (in extreme cases this can lead to death). By taking a benzo one can stop (most of the time) or at least reduce effects from a number of drug overdoses.
I think the latter part was pretty coherent, but if it wasn't, it isn't important enough to try and find another way of telling it.