How long does the anti anxiety effects of alprazolam last for?

On the order of. About 5 hours. But remember everyone's physiology is slightly different and it's effects may last longer or shorter for you depending on how you metabolize the drug.
6 to 8 hrs. The recommended directions are 1 tab every 8 hrs. Strength(?mg) depends on clinical conditions and response of pt.
Depends... It usually takes about 11 hours for half of the amount of alprazolam to be reduced in your body. However, it is considered a short acting anti anxiety medication so the effects may be gone after a few hours( 6). If you have taken it for a long time you may develop tolerance and the dose might need to be adjusted. However, this med can cause overdose and needs to adjusted by your doctor.