Xanax XR 3 mg tablets treat only generalized anxiety disorder and panic disorder. This tablet is a short-term treatment and temporary symptom. Xanax XR 3 tablet doctors recommended doses range from 3 mg to 6 mg once daily. Xanax maintains levels 5 to 11 hours after dosing this tablet in the morning. These tablets are used for a minimum of eight weeks. Xanax XR 3 tablet is very fast-acting. A person may take it before bed to help them fall asleep. Xanax tablets are illegal to take without a prescription from a doctor. Xanax tablets take one pill 1 hour before surgery.