Treatment with APAP will be stopped in healthy volunteers if ALT and/or AST reached three times the ULN. In patients with NAFLD, treatment will be stopped if: ALT or AST reach ≥ three times the upper limit of entry value or ≥ 5 times the ULN; or if there is ALT or AST >3 times ULN and TBili >2xULN or INR >1.5; or if there is ALT or AST >3 times ULN with the appearance of fatigue, nausea, vomiting, right upper quadrant pain or tenderness, fever, rash, and/or eosinophilia (>5%). We follow a conservative approach derived from the FDA guidelines for stopping medications expected to cause drug induced liver injury (DILI). Indeed, the FDA allows continuation of the medication until ALT or AST are >8x ULN in the absence of elevated Tbili or INR. Patients who have hepatotoxicity will have close monitoring of their liver enzymes until they normalize. Taking acetaminophen up to 3g daily has been shown to be safe and acceptable. We have followed very strict criteria for monitoring and stopping rules however in the usually cases of toxicity the patient will be admitted for monitoring.