How long will the over-the-counter diet pill fastin (phentermine) test positive in you urine?

Good luck! I show the generic (phentermine) still as a prescription-only medication. So, whatever is in the over-the-counter version is not likely its true namesake, or potentially in a very reduced strength--either of these may not give you the results you are hoping for, and toxicity risk. Phentermine can show in urine drug screen for 10-14 days per internet resources.