Fever Medicines — Medication Guide, Uses & Safety — Uses, Dosage & Side Effects | MyMedicPlus

Fever medicines, known medically as antipyretics, are drugs that reduce elevated body temperature (fever — generally defined as a temperature above 38°C/100.4°F) caused by infection, inflammation, post-vaccination immune reaction, or other pathological conditions. The most widely used antipyretics are paracetamol (acetaminophen — brand names Tylenol, Panadol, Calpol) and ibuprofen (brand names Nurofen, Advil, Motrin). Both are available over the counter without a prescription in most countries. A third antipyretic, aspirin (acetylsalicylic acid), is effective in adults but is absolutely contraindicated in children and teenagers under 16 years of age (and ideally under 19) due to the risk of Reye's syndrome — a rare but extremely serious condition causing liver failure and brain swelling that can be fatal. This contraindication applies even for viral illnesses such as chickenpox or influenza. Fever is a normal physiological immune response to infection — it is driven by prostaglandins acting on the hypothalamus — and in most healthy adults and children above 3 months a fever between 38–39.5°C does not require medication unless causing significant discomfort. Antipyretics treat the symptom of fever; they do not treat the underlying infection or illness.

Fever medicines are used to lower body temperature and reduce the discomfort and symptoms associated with fever during a wide range of viral and bacterial infections (upper respiratory tract infections, influenza, COVID-19, urinary tract infections, otitis media), post-vaccination fever reactions, inflammatory conditions, post-surgical fever, and dental pain-related fever. They also alleviate the associated systemic symptoms of fever including headache, muscle aches (myalgia), chills, and general malaise, improving patient comfort. Paracetamol is additionally used as a first-line analgesic for mild-to-moderate pain in all age groups, including infants from 2 months, and is the preferred pain reliever in pregnancy. Ibuprofen is used for both fever and pain, and its anti-inflammatory properties make it particularly effective for musculoskeletal pain, dental pain, and menstrual cramps. Both are prescribed or recommended by general practitioners, pediatricians, emergency physicians, and dentists, and widely self-administered under pharmacist guidance. Fever management in pediatric practice is primarily aimed at improving child comfort rather than aggressively normalizing temperature.

Paracetamol (acetaminophen) reduces fever by acting primarily within the central nervous system — specifically on the hypothalamus, the brain's thermostat. It inhibits prostaglandin synthesis centrally (particularly prostaglandin E2 — PGE2), which normally acts on the preoptic area of the hypothalamus to elevate the body's temperature set point during infection. By reducing PGE2, paracetamol allows the body's thermoregulatory set point to return toward normal, prompting heat dissipation through sweating and peripheral vasodilation. It has minimal peripheral anti-inflammatory activity, making it gentler on the stomach than NSAIDs. Additionally, paracetamol may activate descending serotonergic pathways and the endocannabinoid system, contributing to analgesia. Ibuprofen (a non-steroidal anti-inflammatory drug/NSAID) blocks both COX-1 and COX-2 cyclooxygenase enzymes both centrally and peripherally, reducing prostaglandin synthesis throughout the body. This central and peripheral inhibition reduces the fever set point in the hypothalamus and simultaneously reduces prostaglandin-mediated inflammation and pain at the site of tissue injury or infection — giving it both antipyretic and anti-inflammatory properties. Aspirin (acetylsalicylic acid) irreversibly acetylates COX enzymes, reducing prostaglandin production, but also inhibits platelet aggregation irreversibly — one reason it is avoided in children (and not routinely recommended for uncomplicated fever in adults).

Paracetamol adult dose: 500–1000 mg orally every 4–6 hours as needed, with a maximum of 4000 mg (4 g) per 24 hours. For elderly patients, those with liver disease, or regular alcohol drinkers, the maximum is lower — typically 2000 mg/day. Children's doses are strictly weight-based (approximately 15 mg/kg every 4–6 hours, max 4 doses/24 hours); always use weight-specific pediatric liquid formulations with the calibrated dosing syringe provided. Ibuprofen adult dose: 200–400 mg orally every 4–8 hours with food or milk, maximum 1200 mg/day for OTC self-treatment (or 3200 mg/day under medical prescription for inflammatory conditions). Children: approximately 5–10 mg/kg every 6–8 hours (not recommended under 3 months or in dehydrated children). Aspirin (adults only): 300–600 mg every 4–6 hours, maximum 4 g/day — never in under-16s. Suppository formulations of paracetamol and ibuprofen are available for children who cannot swallow medicine. If fever exceeds 39.4°C (103°F) in adults, persists beyond 2–3 days despite antipyretics, or occurs in infants under 3 months, seek medical attention immediately without delay.

Paracetamol is extremely well tolerated at recommended doses and has very few side effects — it is the safest antipyretic for most patient populations including pregnant women, infants (from 2 months), the elderly, and those with gastrointestinal problems or kidney disease. However, paracetamol overdose — taking more than the maximum daily dose, taking multiple paracetamol-containing products simultaneously, or taking it with alcohol — is a leading cause of acute liver failure and can be fatal. Even moderately exceeding the daily maximum for several consecutive days can cause severe liver toxicity. Rare severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis) have been reported — these are very uncommon. Ibuprofen may cause gastrointestinal adverse effects including stomach pain, nausea, and heartburn even at OTC doses — take with food or milk. With regular use, ibuprofen increases the risk of peptic ulcers, gastrointestinal bleeding, kidney impairment (particularly in dehydrated patients), and fluid retention. It is not recommended in dehydrated feverish children, patients with peptic ulcer disease, chronic kidney disease, heart failure, or the third trimester of pregnancy. Aspirin must never be given to children or teenagers under 16 (or under 19 for influenza and chickenpox) due to the risk of Reye's syndrome — a rare but potentially fatal cause of liver failure and encephalopathy associated specifically with aspirin use during viral illnesses in this age group.

Never simultaneously use multiple paracetamol-containing products — many common combination cold and flu medicines (Lemsip, DayNurse, NightNurse, Beechams, Panadol Cold and Flu) already contain full doses of paracetamol. Taking standard paracetamol tablets on top of these products is a leading and easily preventable cause of accidental paracetamol overdose resulting in acute liver failure. Always read ingredient labels carefully. Fever of any level in infants under 3 months requires urgent medical assessment without delay. In children aged 3 months to 5 years with fever over 39°C, seek medical advice if concerned. Fever over 39.4°C (103°F) in adults, fever that does not respond to antipyretics, or fever lasting more than 3 days requires medical evaluation. Seek emergency care immediately if fever is accompanied by any of these red flag features: stiff neck, photophobia, severe headache, non-blanching rash (petechiae/purpura — possible meningitis), confusion or altered consciousness, severe difficulty breathing, or rigid posture. Alternating paracetamol and ibuprofen doses may be recommended by a doctor for high or difficult-to-control fever but should not be initiated by patients without medical advice. Ibuprofen increases the blood levels of lithium — use with caution in those taking mood stabilizers. Paracetamol at regular therapeutic doses modestly increases the INR in patients taking warfarin — more frequent INR monitoring is recommended if using paracetamol regularly.