How long does phentermine stay in your system?

I realize this answer is very, very late ... but may be useful for someone else in future.

Phentermine has a variable elimination half life, which can be anywhere between 16 to 31 hours.

It take 5.5 x elimination half lifes for a medicine to be cleared.

Therefore phentermine may be in your system for up to 170.5 hours (5.5 x 31 hours).

Many factors influence how long a drug remains in your system. Body metabolism, physical condition, state of hydration, age, frequency and method of usage and tolerance will all affect your result. If you know you are going to have a drug test the best thing you can do is stop taking the drug. You could also take your own drug test.

In general Phentermine could last in your system between 1 and 4 days.