Paracetamol overdose is common in developed countries but less than 10% involve large ingestions exceeding 30g or 500mg/kg. High dose acetylcysteine (NAC) has been proposed in patients taking large paracetamol overdoses based on reports of hepatotoxicity despite early initiation of NAC treatment with the commonly used 300 mg/kg intravenous acetylcysteine regimen. The evidence from cohorts of patients treated with the standard NAC regimen after large paracetamol overdoses shows that it is effective in most patients. Small studies in patients whose paracetamol concentration are above the 300mg/L nomogram line show that modification of the standard NAC regimen to provide a total of 400-500 mg/kg NAC over 21-22h may reduce the risk of hepatotoxicity (peak ALT>1000 IU/L) but the impact on development of hepatic failure, liver transplantation and mortality with this approach is presently unknown. Better risk stratification of patients taking paracetamol overdose may allow higher dose NAC and adjunctive treatments such as CYP2E1 inhibition and extracorporeal removal of paracetamol to be targeted to those patients at the highest risk of hepatotoxicity after a large paracetamol overdose.