Paracetamol: a complete guide to the most popular painkiller

Paracetamol sits in almost every home medicine cabinet, and that is exactly why it is so easy to think about it carelessly. It is one of the most thoroughly studied drugs in the world, but one of the most common "household" poisonings is also linked to it. Below I go through how it works, what is actually backed by research, which doses the regulators of different countries give (they do not match), and where the main traps hide.

What this article covers

• What paracetamol is and how it works.
• Doses for adults and children: what is common and how countries differ.
• Why the same dosage is priced differently.
• When paracetamol is more appropriate than ibuprofen and other remedies, and when it is not.
• How to find "hidden" paracetamol in combination medicines.
• Overdose: the mechanism, risk groups, what to do.
• What the latest data say: pregnancy, osteoarthritis, back pain.

What paracetamol is

Paracetamol (the international name; in the US and Canada — acetaminophen) is a non-narcotic analgesic and antipyretic: it reduces pain and fever.

It has almost no clinically significant anti-inflammatory effect in the tissues. So for pain that is based on inflammation, it is not an equal substitute for ibuprofen, naproxen or diclofenac.

How it works

Paracetamol acts mainly in the central nervous system, influencing the transmission of pain signals and thermoregulation. The exact mechanism has not been fully established; the proposals discussed include central inhibition of cyclooxygenase, serotonergic pathways, and metabolites acting through the endocannabinoid system.

The practical upshot:

• it lowers a raised temperature;
• it helps with mild to moderate pain;
• it hardly reduces swelling, redness or inflammatory pain;
• it usually irritates the stomach less than NSAIDs.

Why the drug is so popular

Paracetamol is sold without a prescription, is inexpensive, and suits many people for whom NSAIDs are undesirable: those at risk of ulcers and stomach bleeding, with kidney problems, or taking anticoagulants. It is convenient for short-term control of fever and pain during viral infections, headache, pain after vaccination, and toothache before a dentist visit.

But it is not a "pill for everything": it relieves a symptom, it does not cure an infection, tooth decay, inflammation, migraine or an injury.

What the research shows

Fever and acute pain. Paracetamol lowers fever and helps with some acute pains: headache, toothache, postoperative pain. The effect is most predictable in mild to moderate pain.

Comparison with other analgesics. A Cochrane review of single-dose oral analgesics for acute postoperative pain (Moore et al., 2015) and a separate Cochrane review of the combination (CD010210) showed that ibuprofen together with paracetamol relieves pain better than either drug alone (in the trials, at least 50% relief was achieved by 73% of those taking ibuprofen 400 mg with paracetamol 1000 mg versus 52% on ibuprofen alone). These are data on acute postoperative pain, and they do not mean that paracetamol is useless.

Low back pain. The large PACE trial (Lancet, 2014; 1652 participants with acute low back pain) found no difference in recovery time between paracetamol and placebo: a median of 17 days with regular dosing, 17 with "as needed" dosing and 16 on placebo. A 2016 Cochrane review concluded that for acute low back pain paracetamol is no better than placebo, and that for chronic pain the data are insufficient.

Osteoarthritis. The effect is small. In the British NICE osteoarthritis guideline (NG226, 2022; based on the committee's materials), paracetamol is not recommended because of its small benefit, although the decision remains disputed. What matters more: taking it "out of habit for months" for joint pain is not a good idea; the cause needs assessing and a treatment plan.

Fever in children. The British NICE guideline on fever in children under 5 advises against giving an antipyretic solely to bring down the number on the thermometer: the indication is that the child is distressed and feels unwell. Antipyretics do not prevent febrile seizures. NICE allows using either of the two drugs, but not both at once (from secondary accounts of the guideline; the current version is NICE NG143, check the NICE website).

Doses: what different countries give

This is where the confusion is greatest. There is no single "worldwide" scheme: different countries and different packages carry different limits. All the figures below refer to healthy adults without risk factors and to ordinary over-the-counter forms.

Important clarifications:

• In many countries 4 g per day is regarded as the upper threshold above which the risk of liver damage rises sharply. But in the US the maker of the best-known brand itself lowered the maximum for its products to 3 g in 2011–2012, explaining that people accidentally exceed the dose by taking several paracetamol-containing products at once. At the same time, a number of packages in the US still say "no more than 4000 mg per day" as the threshold for severe liver damage. Look at the figure on your own package.
• Russian package inserts for adults and children over 12 (body weight over 40 kg) give a maximum of 4 g per day, but in chronic and decompensated liver disease, chronic alcoholism, emaciation and dehydration they limit the day to 3 g.
• The NHS separately notes: if you weigh less than 50 kg, the dose may be lower; check with a doctor or pharmacist.
• The single figure "4 g is normal" is a ceiling, not a target. For many people a sensible daily dose is noticeably lower.

Doses for children

The dose is calculated by body weight or by age, but not "by eye". The approaches also differ:

• Russia (package inserts): about 15 mg/kg per dose, up to 4 times a day at 6-hour intervals, a maximum of 60 mg/kg per day. For children aged 3–6 a maximum of 1 g per day is given, for 6–9 years — 1.5 g, for 9–12 years — 2 g (in the insert for 200/500 mg tablets the drug is contraindicated for children under 3). Without a doctor — no more than 3 days as an antipyretic.
• United Kingdom (NHS and MHRA): doses are tied to age and form, no more than 4 doses a day at intervals of at least 4 hours. For children's syrup 120 mg/5 ml: 3–5 months — 2.5 ml, 6–23 months — 5 ml, 2–3 years — 7.5 ml, 4–5 years — 10 ml. For "6+" syrup 250 mg/5 ml: 6–7 years — 5 ml, 8–9 — 7.5 ml, 10–11 — 10 ml. It should not be given for longer than 3 days without a doctor.
• Infants: for children aged 2–3 months (weighing more than 4 kg, born after 37 weeks) the NHS allows 2.5 ml of children's suspension no more than twice a day; after the meningococcal B vaccination at this age, up to 3 doses are permitted. Children under 2 months are not given paracetamol without a doctor's prescription.

Two practical rules: do not mix syrups of different concentrations (120 mg/5 ml and 250 mg/5 ml are different products) and use the dosing device from the package, not a kitchen spoon. Aspirin is not given to children and teenagers with a viral infection because of the risk of Reye's syndrome.

Why prices differ

If two tablets contain the same amount of paracetamol (for example, 500 mg), their main action is comparable provided quality standards are met. An expensive package does not mean "stronger".

How to choose sensibly

For an adult with ordinary occasional pain or fever, a simple product with a single active ingredient is enough, for example paracetamol 500 mg from a legitimate manufacturer. Check the expiry date, the integrity of the package and the registration in the country of purchase.

An expensive form is justified if it solves a problem: syrup or suppositories for a child, an effervescent tablet for difficulty swallowing, a convenient dosing device. A brand without a different form or composition does not make a product better in itself.

Paracetamol and other remedies

This is not a ranking of "the strongest" but a guide by task.

Paracetamol or ibuprofen

Paracetamol is the more logical choice if you only need to bring down a fever or ease body aches, and the person has an ulcer, a risk of stomach bleeding or other contraindications to NSAIDs.

Ibuprofen is more often more effective if inflammation is involved in the pain: tooth, menstruation, soft tissues, joints. But its risks for the stomach, kidneys and cardiovascular system are more pronounced.

And what about the combination? For adults the NHS explicitly allows taking ibuprofen together with paracetamol if necessary, advising to try each separately first, to take the lowest effective dose and to stop when the pain has gone. For children under 5 with fever NICE does not recommend giving both drugs at the same time and allows alternating only as a fallback if distress returns before the next dose — because of the risk of dosing errors and the lack of proven benefit.

Real-life scenarios

Fever with an acute respiratory viral infection

If fever and body aches get in the way of drinking, sleeping and resting, you can take paracetamol according to the package insert. The goal is how you feel, not necessarily "36.6".

Severe sore throat, shortness of breath, confusion, marked dehydration, rash, chest pain, or a fever that does not go away are grounds for a medical assessment, not for increasing the dose of the antipyretic.

Tension headache

Paracetamol is a sensible first option for an occasional mild or moderate headache. If the headache is sudden and "the worst of your life", with speech disturbance, weakness, high fever or a stiff neck — get help urgently.

Preparations with caffeine sometimes work better, but frequent use of any analgesics can itself sustain a chronic headache.

Toothache

Until you see the dentist, paracetamol will temporarily ease the condition, but will not eliminate tooth decay, pulpitis or an abscess. For inflammatory pain NSAIDs often work better if there are no contraindications. Facial swelling, fever, difficulty swallowing or breathing are grounds for urgent help.

Period pain

Prostaglandins play the key role here, so NSAIDs (ibuprofen, naproxen) are often more effective than paracetamol. When NSAIDs are contraindicated, paracetamol is the safer compromise. Very severe, new or worsening pain, heavy bleeding, fainting — see a gynecologist.

Pain after exercise

For ordinary muscle soreness, time, sleep, nutrition and moderate activity help. Analgesics must not become a way of training through an injury.

Pregnancy and breastfeeding

Paracetamol is still considered the preferred painkiller and antipyretic in pregnancy and breastfeeding: so the NHS writes, and so do Russian package inserts (use the lowest effective dose and the shortest course).

In September 2025 the question became public: claims appeared linking paracetamol in pregnancy with autism. On 22 September 2025 the American FDA announced the start of a process to change labeling, pointing to a possible association but stressing in a letter to doctors that a causal link has not been established and that there are studies pointing the other way. The European Medicines Agency replied that there are no new data requiring a change in recommendations; a 2019 review on children's neurodevelopment found the results inconclusive and established no link. The British regulator MHRA also reminded that untreated pain and fever in a pregnant woman themselves carry risk. In January 2026 a systematic review with meta-analysis was published in the journal Lancet Obstetrics, Gynaecology & Women's Health: in sibling comparisons (which account for shared family and genetic factors) no link was found with autism, ADHD or intellectual disability. A caveat: these are observational data, not randomized trials, and the recommendation remained the same: the lowest dose, the shortest duration, as seldom as possible.

The main danger: overdose

At ordinary doses paracetamol is usually well tolerated. In overdose it can cause severe, sometimes fatal liver damage.

Part of the dose is converted in the liver into a toxic metabolite, NAPQI. Normally it is quickly neutralized by glutathione. When there is too much paracetamol, the glutathione stores are depleted, and NAPQI damages liver cells.

What raises the risk

• Doses higher than stated in the package insert.
• Several paracetamol-containing medicines at the same time.
• Regular alcohol. In American labeling: liver damage is possible with three or more alcoholic drinks daily while taking it; the NHS considers paracetamol unsuitable in alcohol dependence and binge drinking.
• Liver disease (and, according to the NHS, kidney disease as well).
• Malnutrition, emaciation, prolonged fasting, dehydration.
• Some medicines: Russian package inserts warn of an increased risk when taken together with agents affecting liver metabolism; according to the acetylcysteine label, enzyme inducers (for example, isoniazid) also increase the risk.

Russian package inserts also give toxicity benchmarks: in adults liver damage is possible from a single intake of 10 g, and in the presence of risk factors from as little as 5 g.

Drug interactions

The NHS asks you to consult a pharmacist if you are taking:

• warfarin — long-term regular use of paracetamol may enhance the anticoagulant effect and the risk of bleeding (the inserts of British preparations state: with single doses there is no significant effect, with regular intake of 1.5–2 g a day for 5–7 days and longer it is possible);
• flucloxacillin (an antibiotic) — cases of pyroglutamic acidosis (high anion gap metabolic acidosis) have been described, especially in severe illness, sepsis, emaciation and chronic alcoholism;
• metoclopramide and domperidone — the NHS lists these among the drugs requiring caution.

If an overdose has occurred

If you have taken more than the recommended dose, especially together with alcohol or other medicines containing paracetamol, do not wait for symptoms. Call an ambulance or a poison center, and state the name, the dose and the time of intake. In the United Kingdom you call NHS 111 in this case; in the US, Poison Control (the labeling gives the number 1-800-222-1222); in Russia, an ambulance and the local poison center (I did not verify specific numbers in the sources).

Early symptoms (nausea, vomiting, sweating, weakness) may be mild or absent, while signs of liver damage (pain in the right upper abdomen, rising liver enzymes) appear after 24–72 hours and peak on days 3–4. The specific treatment is N-acetylcysteine: maximum protection is achieved if it is started within the first 8 hours, after which effectiveness declines, but treatment is not withheld later either (the time of intake is often reported inaccurately). The blood concentration of paracetamol is assessed using the Rumack–Matthew nomogram, but it is not applicable if the intake was spread over time or the time is unknown — in that case a toxicologist decides.

"Hidden" paracetamol

The main household trap is not a single tablet but a combination of products. Paracetamol is found in cold powders and tablets, in "flu" remedies, in headache preparations and in some combination analgesics, including prescription ones with opioids.

Before taking anything, look at the "active ingredient" or "composition" line. Look for: "парацетамол", "acetaminophen", "APAP", "paracetamol".

An example: two 500 mg tablets in the morning, a "cold" sachet containing paracetamol during the day, and a combination headache tablet in the evening. The doses add up, although the packages look like different medicines.

Combination medicines: benefit and marketing

Combinations are justified when each component addresses a specific symptom: for example, fever, pain and a blocked nose. But "more components" does not mean "better".

Marketing often sells an attractive package, a flavor, a "day/night" format and the promise of a "comprehensive strike against a cold", rather than a new active ingredient. This does not make the product useless, but it is worth asking: which symptom does each component treat, and do I need it?

Packs and sales: how this works in the United Kingdom

Countries restrict sales in different ways to reduce the number of poisonings. In the United Kingdom, in general sale (shops, petrol stations) a pack of paracetamol is no more than 16 tablets, in a pharmacy under a pharmacist's supervision no more than 32; the law forbids selling more than 100 paracetamol tablets without a prescription in one purchase. MHRA recommendations from 2025 advise selling no more than two packs of painkillers per purchase. In Russia, in the US and in a number of other countries I did not find such a single rule on pack size in the verified sources, so I do not assert it.

Common mistakes

• Believing that an over-the-counter medicine cannot be overdosed.
• Taking paracetamol together with a "cold powder" without reading the composition.
• Raising the single dose instead of seeing a doctor when pain is increasing.
• Washing it down with alcohol.
• Taking a painkiller daily for chronic pain without looking for the cause.
• Giving a child a dose "by eye" or using an adult form without an exact calculation.
• Taking it for longer than 3 days (as an antipyretic) without seeing a doctor.
• Believing that an expensive brand is more effective than a plain generic.

Home medicine cabinet

• Plain paracetamol in a clear dosage.
• One NSAID (for example, ibuprofen), only if it is not contraindicated for you.
• A separate remedy for a chronic problem, prescribed by a doctor.
• A thermometer, a measuring syringe for children's forms, and a list of the active ingredients of the medicines you have.

This lowers the chance of buying three versions of the same medicine under different names.

A short checklist before taking it

1. What do I want to relieve: fever, pain or inflammation?
2. Do I have liver or kidney disease, alcohol use, an ulcer, pregnancy, warfarin or flucloxacillin? Do I weigh less than 50 kg?
3. Which active ingredients have I already taken today?
4. Is there no paracetamol in my cold remedy?
5. Are there any alarming symptoms that call for medical help?

The bottom line

Paracetamol is neither a "dummy pill" nor a miracle drug. It is a well-studied remedy for fever and moderate pain, especially useful when NSAIDs are undesirable. Its main risk is not the stomach but the liver, when the dose is exceeded or several medicines add up unnoticed. For osteoarthritis and low back pain the evidence of its benefit is weak.

A sensible choice: buy by active ingredient, do not overpay for a brand, take the lowest effective dose for a short course, and always check the composition of combination products and the maximum daily dose on the specific package: it depends on the country and the manufacturer.

Sources

• NHS: How and when to take paracetamol for adults
• NHS: Who can and cannot take paracetamol for adults
• NHS: How and when to give paracetamol for children
• MHRA Drug Safety Update: Paracetamol, updated dosing for children
• MHRA: Best practice guidance on the sale of medicines for pain relief (2025)
• Paracetamol package insert (medi.ru, citing GRLS)
• EMA: Use of paracetamol during pregnancy unchanged in the EU
• AEMPS: no evidence of a causal link between paracetamol in pregnancy and autism
• Prenatal paracetamol exposure and child neurodevelopment: a systematic review and meta-analysis (2026)
• Cochrane: Paracetamol for low back pain (CD012230)
• Pharmaceutical Journal: Paracetamol ineffective for acute lower back pain (PACE)
• NICE NG226: economic analysis of pharmacological treatments for osteoarthritis
• Pharmaceutical Journal: NICE recommends exercise over analgesics for patients with osteoarthritis
• GPnotebook: NICE guidance on paracetamol and ibuprofen for fever in children under 5
• Cochrane: Single dose oral ibuprofen plus paracetamol for acute postoperative pain (CD010210)
• Johnson & Johnson: McNeil announces new dosing instructions for Tylenol products
• DailyMed: Tylenol Extra Strength (FDA-registered label)
• FDA: Kroger Acetaminophen Drug Facts (liver warning)
• MSD Manual: Acetaminophen poisoning
• Ontario Poison Centre: Rumack–Matthew nomogram
• eMC (UK): Paracetamol 500mg tablets, SmPC (warfarin, flucloxacillin)