A little info I found
"Phentermine has an adult half-life of between 7 and 20 hours, and peaks in the bloodstream 8 hours following administration. Assuming a seven hour half-life, over 90% of the medication would theoretically be cleared from your system in 28 hours. Assuming a 20 hour half-life, it would take approximately 80 hours for most to clear."
Good Luck to you!!