Most common Xanax side effects:

The most common side effects of this anti anxiety medication include mild drowsiness during the first few days of therapy.  Weakness and confusion may occur, especially for seniors and others who may be sickly or otherwise physically compromised.  If these effects persist, you should contact your doctor immediately.

Less common Xanax side effects:

Some of the side effects experienced to a lesser degree among individuals taking this anti anxiety medication include depression, lethargy, disorientation, headache, inactivity, slurred speech, stupor, dizziness, tremors, constipation, dry mouth, nausea, inability to control urination, sexual difficulties, irregular menstrual cycle, changes in heart rhythm, low blood pressure, fluid retention, blurred or double vision, itching, rash, hiccups, nervousness, inability to fall asleep, and occasional liver dysfunction.  If you experience any of these Xanax side effects, you should stop taking the medication immediately and contact your doctor.

Rare Xanax side effects:

Medical experts report that rare side effects can occur in almost any part of the body when taking this anti anxiety medication.  You should contact your doctor immediately if you experience any side effects not listed above.

Drug interactions:

Xanax is a central nervous system depressant.  You should avoid alcohol and other tranquilizers, narcotics, barbiturates, monoamine oxidase inhibitors (MAOI’s), antihistamines and antidepressants while taking this medication.  If you're taking Xanax with these other medications, you may experience an excessive amount of depression, tiredness, sleepiness, breathing difficulties and related symptoms.

Smoking is believed to reduce the effectiveness of Xanax by increasing the rate at which it is broken down by the body.

The effects of Xanax may be prolonged when taken together with cimetidine, oral contraceptives, disulfiram, fluoxetine, itraconazole, ketoconazole, metoprolol, probenecid, propoxyphene, propranolol, rifampin, and valproic acid.Theophylline may reduce Xanax’s sedative effects.

If you take any antacids, you should separate them from your Xanax dose by at least one hour to keep them from interfering with the absorption of this anti anxiety medication into the bloodstream.Xanax may raise digoxin blood levels and the chances of digoxin toxicity.The effect of levodopa may be decreased if it is taken along with this anti anxiety medication.Combining Xanax with phenytoin may increase its blood concentrations in the chances of phenytoin toxicity.