Written by Chloe Doris

Last Reviewed: September 2019

Review Due: September 2020


mechanism of action2,3,4

The mechanism of action of paracetamol is not completely understood. It is considered to be a weak inhibitor of prostaglandin synthesis with some selectivity for brain COX2. 


Prostaglandins act to sensitise nociceptors to inflammatory mediators such as bradykinin. Paracetamol decreases the production of prostaglandins by inhibiting the enzyme cyclo-oxygenase (COX) and thus decreasing the sensitisation of nociceptors.

Paracetamol is similar to NSAIDs in that it has analgesic and antipyretic actions, but it has very weak anti-inflammatory properties – likely due to its selectively acting within the brain.


Mild to moderate pain



side effects1

Side effects from paracetamol are rare but can include:

Allergic reaction (rash/swelling)

Flushing, hypotension and tachycardia (associated with IV administration)

Liver and kidney disease in the case of overdose



Patients should not take paracetamol if:

they have had an allergic reaction to paracetamol in the past

they have liver or kidney problems

they regularly drink more than 14 units of alcohol a week

they take medicine for epilepsy or tuberculosis


dose adjustments2,5

Hepatic impairment: dose-related toxicity – avoid large doses

Renal impairment: increase IV infusion dose interval to every 6 hours if eGFR <30mL/minute/1.73 m2.5



Paracetamol can increase the anticoagulant effect of the following drugs: Acenocoumarol, Warfarin, Phenindione 


Heavy alcohol consumption can cause severe liver damage 

Many other drugs can increase the risk of hepatotoxicity when given with paracetamol


Don’t take paracetamol with other paracetamol-containing medications, including co-codamol.



  1. NHS. Paracetamol for Adults. 2019.

  2. Rang H.P, Ritter J.M, Flower R.J, Henderson G. Rang & Dale’s Pharmacology. 8th Ed. Elsevier Churchill Livingstone; 2016. Page 526-527.

  3. NICE. NSAIDs. 2019.

  4. Rang H.P, Ritter J.M, Flower R.J, Henderson G. Rang & Dale’s Pharmacology. 8th Ed. Elsevier Churchill Livingstone; 2016. Page 332.

  5. British National Formulary. Paracetamol.

  6. British National Formulary. Interactions: Paracetamol.

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