How long does it take for Tylenol to kick in?

Acetaminophen (better known by the brand name Tylenol) is a standby you probably keep in your own handbag or medicine cabinet to fight headaches, pain and fever, and now that you’re a parent, it may be the first thing you grab at the drugstore when baby is feeling under the weather. But giving babies, especially the tiniest ones, any type of medicine takes a little extra care and guidance. Here’s what you need to know to safely give Infant Tylenol to help reduce baby’s fever.

First, the basics: Acetaminophen is one of two main types of over-the-counter pain relief. The other is nonsteroidal anti-inflammatory drugs (NSAIDs), a category that includes ibuprofen, naproxen and aspirin—though aspirin should never be given to children under 18 unless directed by a doctor, because it could cause a potentially life-threatening disease called Reye’s syndrome.

Infant Tylenol used to be available in two different formulations: infant drops for babies and an oral suspension for older kids. The drops had a higher concentration of medicine per milliliter, so parents would only have to give a tiny amount to their babies, but there were worries that it could lead to accidental overdoses, so in 2011 the drops were phased out. Now, like Children’s Tylenol, Infant Tylenol comes in an oral suspension, which has a lower concentration of medicine and allows for much safer Infant Tylenol dosing. To make sure you’re purchasing the new, correct version of infant acetaminophen, the bottle should list the concentration as 160mg/5mL. And if you still have some of the drops in your medicine cabinet left over from an older sibling, toss it out and buy a new bottle of the oral suspension.

Infant Tylenol Dosage Chart by Weight

You’ll notice on the bottle of Infant Tylenol that it doesn’t give dosages for children under 2 years old, but instead says to call your doctor. As long as you talk to your doctor first to get the correct Infant Tylenol dosage, there’s actually no age that’s considered too young to administer the medicine—in fact, Infant Tylenol is sometimes even given to preemies.

Baby’s pediatrician will be able to recommend whether or not to give the medicine to baby and what the correct Infant Tylenol dosage should be based on your child’s weight. “I recommend that parents review the correct dosage at every well-baby checkup, depending on the current weight of baby,” says Wendy Sue Swanson, MD, a Wisconsin-based pediatrician. “Write down the dosage on a sticky paper and attach it to the bottle.” Once baby reaches 2 years old, you can go ahead and follow the guidelines on the bottle.

If you do need to give your child Infant Tylenol, here are the current Infant Tylenol dosage guidelines your doctor will likely advise for the 160mg/5ml syrup oral suspension formulation, according to the American Academy of Pediatrics:

When Should You Give Infant Tylenol?

“Acetaminophen is great for when your baby is in pain, like when they’re teething, have an ear infection or have a minor injury,” Swanson says. When baby has a viral infection or cold, she prefers Infant Tylenol over ibuprofen, since ibuprofen may cause side effects like an upset stomach (although it’s not common).

If baby is under 3 months old and has a fever, always call your doctor immediately before giving your child any medication. “We always like to see the baby before dosing with medicine,” Swanson says. “First of all, we want to know why the baby is crying and feverish—infection can spread more rapidly in an infant than in an older child. Secondly, we need to know exactly how much the baby weighs so you can give the correct dose.” She adds that for babies over 6 months old, a day or two of fever isn’t completely dangerous. “We use medicine to decrease any discomfort your baby feels, not to change the number on the thermometer.” If, however, any child’s fever is over 103 degrees Fahrenheit (39.4 Celcius) or symptoms don’t improve after three days, you should always call your doctor.

One time you don’t want to give Infant Tylenol? Before baby goes for shots. In the past, doctors would recommend giving baby Infant Tylenol before a vaccination to help prevent pain and a possible fever from developing, but that’s changed. “There is new data showing that if you give the child a dose of acetaminophen before the shot, it may make the immunization less effective,” Swanson says. And as for that low fever baby may run after being vaccinated, well that’s just a sign the body’s immune system is kicking in properly, and it usually doesn’t need to be treated. If baby seems fussy and uncomfortable after she’s gotten her shots, though, you can go ahead and give her Infant Tylenol, Swanson says.

How Often Can You Give Infant Tylenol?

You may give baby the correct Infant Tylenol dosage every four hours, but no more than five times in one 24-hour period, says Alexis Phillips, DO, a pediatrician in the Houston, Texas, area. “Do not exceed 48 hours at maximum dose,” she cautions. “Also, Tylenol should not be taken more than seven days in a row without discussing it with your pediatrician.”

How Long Does Infant Tylenol Take to Work?

Infant Tylenol takes 30 minutes to start working, Phillips says, and will reach maximum effect after one hour. If baby’s fever goes away for more than 24 hours and then comes back, or if baby has a fever for more than 72 hours, call your pediatrician.

How to Safely Give Infant Acetaminophen

Ready to help baby feel better? Follow these tips to make sure you medicate baby safely.

• Make sure you have baby’s correct weight To ensure you’re giving baby the correct Infant Tylenol dosage, you need to know how much your child weighs. “If you haven’t been to the doctor in a while, place your child on the scale at home,” Phillips says. (You can also stand on a scale holding baby and subtract your own weight from the total.)

• Carefully read the instructions on the bottle
That means turning the bathroom light on, even if it’s in the middle of the night (also important for measuring the correct dose). Then shake well to evenly distribute the active ingredients.

• Use the right measuring device
Once you’ve figured out the correct Infant Tylenol dosage (based on your doctor’s instructions or the chart above), be sure to only use the measuring device that comes with the bottle—it’s a good idea to always store them together after washing. For infants, it’s usually a syringe. For children 2 and over, it’s most likely a small measuring cup. Since some medications are measured in teaspoons, some in milliliters and some in ounces, never mix and match measuring devices. “You should also never use a kitchen spoon, which isn’t accurate, and you definitely don’t want Grandma just eyeballing it and saying, ‘That looks right,’” Swanson says.

• Keep track of doses
It’s easy to forget when you last gave baby a dose of infant acetaminophen, so make sure to write it down every time. Tylenol even has a handy fever diary app you can download to your phone. It’s especially important to keep track if you have multiple caregivers treating baby—you don’t want anybody accidentally skipping or repeating doses.

• Help baby keep the medicine down
If using a syringe, dispense the liquid slowly into baby’s mouth—aim for the side pocket between the gum and the cheek, toward the rear of the mouth (this is the least taste-sensitive area). If baby spits some of the medicine out, don’t give any more. Instead, wait until it’s time for the next dose and try this trick: Gently squeeze baby’s cheeks together when you dispense the Infant Tylenol—it will open baby’s mouth, making it harder to spit.

Updated February 2020

Expert bios:

Wendy Sue Swanson, MD, MBE, FAAP, is a Wisconsin-based pediatrician. After writing the Seattle Mama Doc blog on behalf of Seattle Children’s Hospital for 10 years, she now blogs at wendysueswanson.com. She’s also the author of Mama Doc Medicine: Finding Calm and Confidence in Parenting, Child Health and Work-Life Balance.

Alexis Phillips, DO, is a pediatrician with Memorial Hermann Medical Group Pediatrics Atascocita in Atascocita, Texas. She is a graduate of Ohio University Heritage College of Osteopathic Medicine.

Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances. Plus, more from The Bump:

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