How horrible is dropping 4 mg of xanax (alprazolam) on the liver at one time?

Not hepatotoxic: Xanax (alprazolam) is metabolized in the liver to another active compound, and 4 mg is certainly a significant dose. The drug itself is not damaging to the liver, unless it causes low blood pressure, respiratory failure, coma, and death (in which case it should be obvious that the liver wouldn't fare too well). Xanax is unlike tylenol (acetaminophen) or alcohol which ARE directly toxic to the liver

Not usually toxic: A one time dose at that level is not usually toxic, unless there are other factors involved (other meds, prior liver disease, etc.). It might be very sedating, especially if combined with other drugs or alcohol, or if the person taking it isn't used to Xanax, (alprazolam) because that is a high dose, generally. This could be dangerous.

The liver has little: to do with this. The brain, on the other hand, is going to get very drunk, particularly if the individual is not tolerant to sedatives. If this is prescribed, it is TOO MUCH. If it is not prescribed, it is dangerous. Benzos, and Xanax (alprazolam) in particular, can cause a great deal of central nervous system depression with cessation of breathing particularly if combined with alcohol or opiates.