Seroxat is essentially an antidepressant drug.
It's trade name is Paroxetine (in the UK) and it is a selective serotonin reuptake inhibitor (like the famous Proxac). This means that it acts to increase the level of serotonin in the blood and thus counter depressive illness.
As far as side effects go, the most common ones are nausea and vomiting, heart burn, weight loss, a rash, swelling and bone and joint pain.
Despite these, it is a very effective drug but should always be prescribed within the context of other therapies, provided by a doctor or paramedically-trained professional.
Hope that helps,
Dive777