Paracetamol, also known as acetaminophen, is safe at normal doses but can cause severe liver damage in overdose. The antidote is N-acetylcysteine, often abbreviated as NAC, which helps prevent or reduce liver injury if given promptly.
What the antidote does
N-acetylcysteine works by restoring glutathione, a substance the liver uses to neutralize paracetamol’s toxic breakdown product, NAPQI. When glutathione is depleted after an overdose, toxic metabolites can damage liver cells; NAC helps stop that process .
When it is most effective
N-acetylcysteine works best when started within 8 hours of the overdose, and effectiveness falls after that window. Even so, treatment may still help later, so suspected overdose should be treated as an urgent medical emergency.
How it is given
In many hospitals, NAC is given intravenously using a weight-based infusion regimen. Australian guidance states that standard treatment is now a two-bag IV regimen over 20 hours, and the UK guidance also describes IV acetylcysteine as the antidote used in paracetamol overdose management.
When treatment is needed
Doctors decide on NAC using the amount taken, the time of ingestion, and a blood paracetamol level plotted on a treatment nomogram when the ingestion time is known. If the timing is unclear, or in staggered overdoses, NAC should be started without delay.
Important warning signs
Paracetamol overdose can be dangerous even before symptoms become obvious. Nausea, vomiting, right upper quadrant pain, confusion, jaundice, or worsening sleepiness after a suspected overdose need urgent medical assessment.
Medical takeaway
The key point is simple: N-acetylcysteine is the antidote for paracetamol overdose. It is most effective when given early, but treatment should not be delayed when overdose is suspected.