because if you were to take a high dose of effexor rather than tapering it up slowly you would experience severe anxiety and heart palpitations and the shakes and difficulty sleeping etc etc etc. basically... a worsening of your symptoms.

effexor is always started and stopped very gradually indeed.

also: a 'theraputic' dose for one might be sub-theraputic for another and a theraputic dose for another might be an overdose for someone else. everyone is different and wherever possible less is more.