My understanding is that the primary difference has to do with the half-life of the two meds. Xanax works fast, for a short period of time. Ativan works more slowly, but for longer. My pdoc switched me from xanax to ativan some time ago. With xanax I was finding that I would take it when I was feeling panicky and it was great, but then it would wear off suddenly and I was still panicky! This doesn't happen for me with ativan. My pdoc agreed that what was happening was common with xanax...especially the wearing off suddenly part. In my opinion, this is part of why xanax seems to be a bit more addictive then ativan.