Hey. I have been on it for years.
For me, it is used to treat anxiety.
Side effects for me are increased anxiety, some lightheadedness, nausea and loss of appetite. This lasts 1-2 days for me after starting.
I can feel it kicking on within a week or so. By a few weeks I have no 'bad' side effects.
It doesn't make me put on weight and it doesn't seem to affect my appetite much. It does affect libido a bit.
SSRI's (which is what these meds are known as) are the most common to prescribe as generally they work well for people with smaller side effects.
If you want to know anything more specific please feel free to ask.
I only just started on mine again after ceasing due to MS (I'm currently pregnant) so the starting meds is fresh in my mind.