To determine how long Effexor stays in your system, it is necessary to understand the metabolite of its active ingredient – Venlafaxine. Venlafaxine has an elimination half-life of approximately 5 hours (+/- 2 hours) which is extremely short compared to other popular antidepressants. This means that the Venlafaxine should be fully cleared from your system in about 1.15 days (just over a day). However, when accounting for the +/- 2 hour variability of its half-life, some people may excrete the drug in just 16.5 hours, while others may take nearly 2 days (1.6 days) to completely excrete it.