which antidepressant ??

There are many antidepressants and it is sometimes a trial and error.  There is not a one-size-fits-all. You might want to look for a doctor/psychiatrist who specializes in psycho-pharmacology.  I took an SSRI (serotonin selective re-uptake inhibitor) for a short time, then switched to St. John's Wort, which was perfect for me.  It's usually used (in Germany where they've done clinical studies and give it by prescription) for 8 weeks. I took it longer, for about 4 months and should have stopped sooner, it started giving me heart palpitations, but that stopped as soon as I stopped it.

     More recently I was given amitriptyline (Elavil) which is for chronic pain and sleep at small doses (5 - 10 - 20 mg) and an antidepressant at higher doses.  You need to have your liver checked at higher doses.   I found it helpful for a while and still use it occasionally but it can cause people who are bipolar to switch from up to down or vice versa.  I'm not bipolar but supposedly "cyclothymic" which is a low version of mood switches, and I've had a harder time taking it - it tends to depress me, not help that much now. 

    Elavil is one of the older "tricyclic antidepressant"s.  Cyclobenzaprine, which is a muscle relaxer with a quicker 8-hr time frame (less or no hangover) is related but not considered antidepressant.  I still find it helpful sometimes for sleep & muscle spasms/tension.

     If this is for you or someone you know, the person involve needs to work with a clinical social worker, doctor or some kind of therapist with prescribing ability to find the best match.  It's not always obvious because diagnoses are tricky.  I read that fMRI scans of the brain gave better matches to prescribing than patient's descriptions of what they were going through, but I don't think that's commonly done - maybe just when all else fails. 

     That said, Prozac still seems to  be very popular, as is Paxil.  I have heard that Paxil can be very hard to get off of. I was only on it for a couple of weeks and felt it was just a little more than I needed.  But it got me up and running FAST, when I couldn't get myself going and I was very angry and depressed about certain events/people in my life and didn't know what to do, felt trapped.  It's some of that stress that may have triggered my RA.... it was actually while taking Paxil that I first felt some kind of 'congestion' in my wrists and ankles, the body parts that have taken the major brunt of my RA. I don't blame it on the drug, it's what was happening to me at the time...