Are there differences between zoloft and effexor (venlafaxine)?

Yes: Zoloft is a selective serotonin reuptake inhibitor. Effexor (venlafaxine) is a serotonin and norepinephrine reuptake inhibitor. Your doctor may choose either one based on your symptoms of depression and which might help you the most.

Yes: Zoloft is serotonergic in nature. Effexor (venlafaxine) in low doses is also. At higher doses effexor's noradrenergic. Zoloft has fewer significant side effects - Effexor (venlafaxine) has more including at times severe withdrawal effects compared to zoloft. Studies show Effexor (venlafaxine) to be more effective in severe depression than other antidepressants. With its dual nature Effexor (venlafaxine) doesn't seem to lose effectiveness like zoloft.