This makes a big difference because
Venlafaxine (Generic) has a very fast onset
of release which may excite anxiety in some people prone
to anxiety.
Effexor XR has a much slower release and avoids this spike with it's extended release properties. Venlafaxine also has a pretty short half life also, which is why Effexor was designed with this slow release effect. This effect eliminates the spikes and fast drops from the drug in Effexor XR which is Venlafaxine.