How long do the effects of alprazolam 25 mg work last in system?

depends: First of all, i think you are talking about 0.25 mg. 25 mg is a totally different game. If your buddy was not exposed to Alprazolam ( you did not develop tolerance) then it might work for 4 to 6 hours. You are lucky if more. If your question is about how long can Alprazolam be detected in the urine drug screen – it is totally another story. At least 2 to 3 weeks. Even more, depending on the test.