The liver is one of the only organs in the body that is able to replace damaged tissue with new cells rather than scar tissue. For example, an overdose of acetaminophen (Tylenol) can destroy half of a person's liver cells in less than a week. Barring complications, the liver can repair itself completely and, within a month, the patient will show no signs of damage.

However, sometimes the liver gets overwhelmed and can't repair itself completely, especially if it's still under attack from a virus, drug, or alcohol. Scar tissue develops, which becomes difficult to reverse, and can lead to cirrhosis.