The most common medicines that reduce fever are acetaminophen (Tylenol) and ibuprofen (Advil, Motrin). Both are available over the counter, work within 30 to 60 minutes, and are effective for adults and children. A third option, naproxen sodium (Aleve), also lowers fever and lasts longer than the other two. Which one is right for you depends on your age, health conditions, and how long you need relief.
How Fever Reducers Work
A fever happens when your brain’s thermostat, located in a region called the hypothalamus, gets reset to a higher temperature. During an infection, your body produces a chemical called prostaglandin E2, which signals the hypothalamus to raise your temperature set point. You feel cold and start shivering as your body works to reach that new, higher target.
Fever-reducing medicines (called antipyretics) work by blocking the enzyme that produces prostaglandin E2. With less of this chemical reaching the brain, the thermostat resets back toward normal and your body begins cooling itself through sweating and increased blood flow to the skin. The medicines don’t stop your body from producing heat, so they won’t push your temperature below its normal range.
Acetaminophen (Tylenol)
Acetaminophen is the most widely used fever reducer. It starts working in about 30 to 45 minutes and lasts 4 to 6 hours. It’s gentle on the stomach and safe for most people, including pregnant women in the first two trimesters and those who can’t take anti-inflammatory drugs.
The main risk with acetaminophen is liver damage, which happens when people take more than the recommended amount or combine it with alcohol. Many cold and flu products already contain acetaminophen, so it’s easy to accidentally double up. Always check the active ingredients on any combination products you’re taking. Adults should not exceed 3,000 to 4,000 mg in a 24-hour period, and people with liver problems should use a lower dose or avoid it entirely.
Ibuprofen (Advil, Motrin)
Ibuprofen belongs to a class of drugs called NSAIDs (nonsteroidal anti-inflammatory drugs). It reduces fever and also fights inflammation, which can make it a better choice when your fever comes with body aches, sore throat, or joint pain. It kicks in within 30 to 60 minutes and lasts 4 to 6 hours.
Because ibuprofen affects prostaglandin production throughout the body, not just in the brain, it carries some additional risks. It can irritate the stomach lining, especially in people with a history of peptic ulcers. It also reduces blood flow to the kidneys, so people with kidney disease should avoid it. Other groups who should skip ibuprofen include those with a history of NSAID allergies, people who have had coronary artery bypass surgery, and women in the third trimester of pregnancy.
Naproxen Sodium (Aleve)
Naproxen sodium is another NSAID that works similarly to ibuprofen but lasts significantly longer, up to 12 hours per dose. This makes it a practical option if you want fewer doses throughout the day. It takes about 30 to 60 minutes to start working. The same precautions that apply to ibuprofen apply here: avoid it if you have kidney problems, stomach ulcers, or NSAID sensitivity. Naproxen is not recommended for children under 12 without a doctor’s guidance.
Aspirin: Not for Children or Teens
Aspirin reduces fever in adults, but it should never be given to children or teenagers. Aspirin use during a viral illness like the flu or chickenpox is linked to Reye’s syndrome, a rare but serious condition that causes swelling in the brain and liver. In Reye’s syndrome, blood sugar drops while ammonia and acidity levels rise, and fat builds up in the liver. Children with certain metabolic conditions are at even higher risk. For anyone under 18 with a fever, stick with acetaminophen or ibuprofen.
Choosing Between Them
For most healthy adults, acetaminophen and ibuprofen work about equally well at bringing down a fever. The choice often comes down to your other symptoms and your health history:
- Stomach sensitivity or ulcer history: Acetaminophen is safer for the digestive tract.
- Liver problems or heavy alcohol use: Ibuprofen or naproxen is the better choice.
- Kidney disease: Acetaminophen is preferred, since NSAIDs reduce kidney blood flow.
- Inflammation, body aches, or sore throat: Ibuprofen or naproxen may provide more relief because they target inflammation directly.
- Wanting fewer doses: Naproxen lasts up to 12 hours compared to 4 to 6 for the others.
Should You Alternate Medicines?
Alternating acetaminophen and ibuprofen is a common practice, with one survey finding that 50% of pediatricians have recommended it. However, the evidence behind this approach is weak. Studies consistently show that alternating provides little or no advantage over using a single medicine. More importantly, juggling two drugs with different dosing schedules increases the risk of accidental overdose, especially in children.
There’s also a theoretical concern about kidney toxicity when the two drugs are combined. Ibuprofen reduces a protective substance called glutathione in the kidneys, and acetaminophen’s breakdown products rely on glutathione to be safely cleared. Three case reports have documented reversible kidney failure with the combination, though this hasn’t been confirmed in larger studies.
The safest approach is to pick one medicine and use it at the recommended dose. If a fever isn’t responding, ensure you’re dosing correctly by weight (especially for children) before adding a second medicine. If you do alternate, keep a written log of what you gave and when.
Dosing for Children
Children’s doses are based on weight, not age. A 3-year-old who weighs more than average needs a higher dose than the age label suggests, and vice versa. Acetaminophen can be given every 4 to 6 hours, with no more than 5 doses in 24 hours, and should not be given to infants under 8 weeks old. Ibuprofen can be given every 6 to 8 hours, with no more than 4 doses in 24 hours, and should not be given to infants under 6 months old.
Children over 95 pounds can typically take adult-sized doses of ibuprofen (500 to 650 mg every 6 to 8 hours), but should not exceed 4,000 mg in a day. Use the measuring device that comes with liquid formulations rather than a kitchen spoon, which is unreliable.
When a Fever Needs Attention
Not every fever needs medicine. Fever is your immune system’s response to infection, and moderate fevers in otherwise healthy people often resolve on their own. The goal of treatment is comfort, not hitting a specific number on the thermometer.
Temperature thresholds that signal higher risk vary by age. For babies 3 months and younger, any temperature above 100.4°F (38°C) is considered potentially serious. For children between 3 and 36 months, temperatures above 101.3°F (38.5°C) deserve closer attention. For older children and adults, a fever above 103°F (39.4°C) is considered high. A fever lasting more than three days in an adult, or one accompanied by stiff neck, confusion, difficulty breathing, or persistent vomiting, warrants prompt medical evaluation regardless of the temperature reading.