Xanax 0.5 mg tablet used to treat anxiety and panic disorders works by enhancing the effect of a certain natural chemical of the body. This tablet is adult at first 0.25 to 0.5 milligrams three times a day. Xanax is a controlled drug that is illegal to take without a prescription from a medical doctor. many people the drug helps with anxiety and promotes sleep.it is not good for treating insomnia