Under normal circumstances and without further complications, the liver repairs itself in 30 days from a case such as a Tylenol overdose. This occurs even with 50 to 60 percent of liver cells being damaged, according to University of Iowa Health Care.
The liver is a unique organ in the body because it is the only one that can regenerate, explains University of Iowa Health Care. In all other organs, damaged tissues are replaced with scarring. This can also happen to the liver if regeneration is stunted or there is progressive development of scar tissue. Factors contributing to a liver not being able to repair itself are viruses and over-consumption of drugs or alcohol. Cirrhosis, which is severe scarring of liver tissues, indicates late stage liver disease and is usually followed by further complications.