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Paracetamol is the best-selling over-the-counter pain reliever in Germany and can be found in almost every medicine cabinet worldwide. It relieves pain and lowers fever — quickly, effectively and usually well tolerated. But behind the alleged harmlessness lies a serious risk: Paracetamol is the most common cause of drug-related acute liver failure in the Western world.
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If an overdose is suspected, contact the poison emergency number immediately (030 19240 in Germany; in the UK, NHS 111, or 999 in an emergency) or the emergency department – even without symptoms. This article does not replace medical advice.
Paracetamol is the best-selling painkiller worldwide and the most frequently recommended analgesic in pregnancy and in children. Despite its apparent harmlessness, paracetamol is at the same time the most common cause of medication-induced acute liver failure in Germany. This contradiction is explained by the narrow window between the therapeutic and the toxic dose.
| Property | Details |
|---|---|
| Active substance | Paracetamol (acetaminophen, APAP) |
| ATC code | N02BE01 (anilides) |
| Substance class | Non-opioid analgesic / antipyretic (not an NSAID!) |
| Available forms | Tablets, effervescent tablets, syrup, suppositories, infusion solution, granules |
| Half-life | About 1.5–2.5 hours |
| Max. daily dose (adults) | 4,000 mg (4 g) – in risk patients: 2,000 mg (2 g) |
| Max. pack size over the counter | 20 tablets of 500 mg (= 10 g total amount) |
| Onset of action | About 30–60 minutes |
| Special feature | Not an NSAID – no anti-inflammatory effect |
The exact mechanism of action of paracetamol is, despite decades of research, not fully clarified – a pharmacological curiosity for such a long-established medicine. Unlike NSAIDs such as ibuprofen, paracetamol inhibits cyclo-oxygenase (COX) in peripheral tissues only very weakly. Instead, it acts predominantly in the central nervous system: it inhibits COX-2 in the brain and spinal cord and reduces prostaglandin synthesis there. In addition, influences on the endocannabinoid and the serotonergic system are discussed.
This is the clinically most important difference: paracetamol has no relevant anti-inflammatory effect. With pain that arises primarily from inflammation – joint inflammation, a sports injury with swelling, gum inflammation – ibuprofen is pharmacologically the better choice. Paracetamol, by contrast, has its strengths where stomach tolerability counts, where a heart risk or kidney risk restricts NSAIDs, and everywhere that pain is not inflammatory in nature – headaches, fever, period pain.
The standard dosing for adults: 500–1,000 mg every 4–6 hours, a maximum of 4,000 mg per day. In risk patients (liver disease, regular alcohol consumption, underweight, malnutrition) the limit is a maximum of 2,000 mg per day. There must be at least 4–6 hours between the individual intakes.
In children, paracetamol is dosed strictly by body weight: 10–15 mg per kilogram of body weight as a single dose, every 4–6 hours, a maximum of 60 mg/kg of body weight per day. The most important rule of thumb: never give paracetamol suppositories and syrup at the same time – this leads to a double dose.
| Body weight | Age (approx.) | Single dose suppository | Single dose syrup (40 mg/ml) |
|---|---|---|---|
| 3–4 kg | Newborns | 75 mg | Only under medical supervision |
| 5–8 kg | 3–12 months | 75–125 mg | 1.25–2 ml |
| 8–12 kg | 1–3 years | 125–250 mg | 2–3 ml |
| 12–20 kg | 3–6 years | 250 mg | 3–5 ml |
| 20–30 kg | 6–9 years | 250–500 mg | 5–7.5 ml |
| 30–43 kg | 9–12 years | 500 mg | 7.5–10 ml |
Paracetamol has a clear advantage when taking it: it can be taken with or without food – as a non-NSAID it does not attack the stomach lining. The most important rules:
Record all medications and intake times in your digital medication plan.
This is the pharmacological core that every paracetamol user must know. Paracetamol is broken down in the liver via several routes. The dangerous route: a small part of the active substance is converted by the enzyme CYP2E1 into a highly toxic intermediate – NAPQI (N-acetyl-p-benzoquinone imine). Normally, NAPQI is immediately neutralised and excreted by the body's own antioxidant glutathione.
With an overdose, so much NAPQI is produced that the glutathione stores of the liver are exhausted. The un-neutralised NAPQI then binds covalently to liver cell proteins and destroys the liver cells irreversibly. The treacherous thing about it: this destruction takes place with a delay of 24–72 hours. During this time those affected often still feel relatively well or have only mild symptoms – while the liver is already being massively damaged.
The critical dose of 7.5–10 g applies to a healthy adult with normal glutathione reserves. With several risk factors, this threshold can be considerably lower. Risk factors are: regular alcohol consumption (induces CYP2E1 and exhausts glutathione), pre-existing liver diseases (hepatitis, cirrhosis), malnutrition or eating disorders (low glutathione reserves), and the intake of medications that induce CYP2E1 (isoniazid, rifampicin). For these risk groups the daily maximum dose is 2,000 mg.
| Stage | Period | Symptoms |
|---|---|---|
| Stage 1 | 0–24 hours | Nausea, vomiting, upper abdominal pain – or symptom-free! |
| Stage 2 | 24–72 hours | Liver values rise, upper abdominal pain on the right, jaundice begins |
| Stage 3 | 72–96 hours | Liver failure: jaundice, clotting disorder, impaired consciousness, organ failure |
| Stage 4 | From day 4 | Recovery or death / liver transplant |
When used as intended, paracetamol is one of the painkillers with the fewest side effects. Unlike NSAIDs, it causes no stomach lining damage, no blood pressure rise, and no relevant impairment of kidney function. In rare cases the following can occur: allergic skin reactions, blood count changes (thrombocytopenia), and bronchospasm in patients with analgesic-induced asthma.
An important long-term problem: with too frequent use (over 10 days per month) there is a risk of a medication-overuse headache. This is a paradoxical phenomenon: the painkiller itself causes headaches when it is taken too often. Anyone who notices that they need paracetamol for headaches more and more frequently should speak to the doctor.
This is the most common paracetamol problem in practice: patients take a flu remedy (e.g. Grippostad C, Wick DayMed, Wick MediNait, Thomapyrin, Neuralgin) and additionally paracetamol tablets for headaches. Many of these combination products contain paracetamol as one of their active substances – without that being prominently visible on the front of the packaging. The maximum daily dose of 4 g can thus be exceeded unnoticed. Check the ingredients of all other medications before every paracetamol intake. The brite interaction check recognises such duplications automatically.
| Substance / medication | Interaction | Recommendation |
|---|---|---|
| Alcohol | Exhausts glutathione, increases NAPQI formation – a massively increased liver risk | No alcohol. With chronic consumption: max. 2 g/day |
| Combination products (Grippostad, Wick, Thomapyrin) | Often contain hidden paracetamol – a duplication! | Always check the package leaflet, calculate the total dose |
| Marcumar / warfarin | Paracetamol can enhance the effect of warfarin | Check the INR more often |
| Carbamazepine, phenytoin, rifampicin, isoniazid | Induce CYP2E1, more toxic NAPQI is formed | Reduce the daily dose to max. 2 g! |
| Metoclopramide / domperidone | Accelerate gastric emptying → faster onset of action | Can be used therapeutically (e.g. with migraine) |
| Colestyramine | Reduces paracetamol uptake | At least 1 hour apart |
