Can Xanax (alprazolam) at a. 05 dose can cause permanent erectile dysfunction after you've stopped taking it?

No. And i think you mean 0.5 mg. There are no reports i can find of long-term erectile dysfunction after benzodiazepines are stopped. However, the anxiety for which you took the xanax (alprazolam) might have something to do with it. You need evaluation by a men's health specialist.