One theory is that the relatively short half life of paroxetine and venlafaxine make these two drugs more problematic. This leads to a withdrawal strategy that advocates switching from paroxetine or other drugs to fluoxetine.The second is that paroxetine and venlafaxine are relatively more potent serotonin reuptake inhibitors and this theory leads to a switch to less potent serotonin reuptake inhibitors such as citalopram
see also -
http://www.clinical-depression.co.uk/half_life.htm
Seroxat/paroxetine half life = 21 to 26 hours,
Efexor/venlafaxine half life = 5 (5 to 11) hours
