Bought what were sold as 2mg Xanax bars from a street source. They looked right — white, rectangular, "XANAX" imprint, scored into four pieces. I took a quarter thinking it would be 0.5mg alprazolam.
T+0:15 the onset was wrong. Alprazolam takes 20-40 minutes for me. This hit fast and hard. Instead of the clean anxiolytic feeling, I felt heavy, sedated, and dizzy. My coordination was severely impaired. This was not alprazolam.
I later got a reagent test kit and tested the remaining bars. No benzodiazepine reaction. I sent a sample to a mail-in drug checking service — it came back as flualprazolam, a designer benzodiazepine that's roughly 2-4x more potent than alprazolam with a longer duration and different safety profile.
Some pressed bars contain flualprazolam, etizolam, clonazolam (extremely potent and dangerous), or even fentanyl. You cannot tell by looking at them. The press quality means nothing — anyone can buy a pill press.
If you use benzodiazepines obtained outside a pharmacy: reagent test at minimum, mail-in drug checking if available, and always start with a quarter or less of any new batch. The assumption that a bar contains 2mg alprazolam could be a fatal miscalculation if it contains 0.5mg clonazolam instead.