In my experience, it can be as difficult a process as switching from an SSRI to a non-SSRI. I actually started on Paxil... it was my first drug... and it was initially prescribed for panic disorder. It ended up making my panic attacks more frequent, longer, and more severe. It just didn't work out for me. So we switched to Zoloft. It's weird how so many different drugs of the exact same class can affect the same one person so differently. But yeah, it can be relatively difficult because they can have such different effects.