I've taken 100mg seroquel (quetiapine) for a month and have begun tapering off by 12.5mg how long will the drug stay in my system after i stop taking it fully?

Quickly: Seroquel (quetiapine) would be out of the blood steam approximately 35 hours after the last dose.

1.5 days: Half-life of seroquel (quetiapine) is 7 hours. It takes approximately 6 half lives for a drug to be eliminated from your system. 5*7/24= aprox. 1.5 days. Tapering down by 12.5 every 3 days is the safest way to discontinue any psychotropic medication. Take care.