It takes anywhere from five to 10 days for the body to eliminate approximately 99 percent of Remeron, also known as mirtazapine, after oral administration, states RxList. The variance in this number is attributable to gender, age and ethnicity, with women consistently taking longer to flush Remeron from their systems.
The half-life of Remeron after oral administration ranges from 20 to 40 hours, according to RxList. Six half-lives correspond to a reduction of Remeron concentration in blood plasma to 1.5625 percent of its original value, meaning that almost all of the Remeron has then been eliminated. Six half-lives equates to 120 to 240 hours, or five to 10 days.