How long does it take for marijuana to get out your system to pass a mouth swab test?

Weeks to months: Thc is stored in body fat and slowly metabolized, so it builds up in the body with increased use. I'm not familiar with mouth swab testing, however for urine drug testing results depend on how much and how frequently a patient has used thc. A test will usually remain positive for 1 week after one-time or rare light use, 1 month after heavy use, or several months for habitual, heavy use.