The HiSNAP Trial aims to test conventional (200mg/kg) versus higher (450mg/kg and 600mg/kg) doses of the drug N-Acetylcysteine (known as NAC) which is commonly used to treat the effects of paracetamol overdose. The breakdown of paracetamol will be primarily measured through serum concentrations of metabolites 12hrs after treatment starts, with other outcomes collected from urine samples, clinical bloods, symptoms questionnaires, and admissions data. Adults presenting to ED with larger overdoses (double the clinical cut-off for treatment) will be recruited over a period of two years – aiming for a total of 90 from both RIE and SJH sites.