How can snri's such as cymbalta and effexor (venlafaxine) control anxiety if they work on norepinephrine..would not this increase anxiety?

Very right you are!: In my practice I never use these medications, also Wellburtrin and Pristiq, (desvenlafaxine) for anxiety treatment precisely for this reason . And it's not a hypothetical concern as time after time they worsen anxiety in my humble opinion. SSRI's are much more reliable save Paxil (too short acting leading to withdrawal effects). Take care.