The vitamin K shot given to newborns contains 1 mg of phytonadione, a synthetic form of vitamin K1, dissolved in a tiny 0.5 mL injection. Alongside the active ingredient are a small number of inactive ingredients that help the vitamin dissolve and stay stable. Here’s a full breakdown of what’s in it and why each component is there.
The Full Ingredient List
Each 0.5 mL dose contains:
- Phytonadione (vitamin K1), 1 mg: The active ingredient. This is a lab-made version of the same vitamin K1 found naturally in green leafy vegetables. It’s identical in function to the vitamin K your body uses every day.
- Polysorbate 80, 10 mg: An emulsifier that helps the fat-soluble vitamin K blend evenly into the liquid so the dose is consistent. Polysorbate 80 is widely used in foods, cosmetics, and medications.
- Propylene glycol, 10.4 mg: A solvent that helps keep the vitamin K dissolved in the solution. It’s also commonly found in foods, medications, and personal care products.
- Sodium acetate anhydrous, 0.17 mg: A buffering agent used to keep the solution’s pH in a safe, stable range (between 3.5 and 7.0).
- Glacial acetic acid, 0.0002 mL: A trace amount of acetic acid (the same acid found in vinegar) also used to fine-tune the pH.
That’s the complete list for the standard preservative-free formulation. The total volume, half a milliliter, is roughly one-tenth of a teaspoon.
Preservative-Free vs. Preserved Versions
Some manufacturers, including Pfizer, produce a version that contains benzyl alcohol (9 mg per mL) as a preservative. Benzyl alcohol can cause serious adverse effects in newborns when given intravenously, so the labeling explicitly recommends using a benzyl alcohol-free formulation for neonates and infants when one is available. In practice, most hospitals in the U.S. stock the preservative-free version for newborn use. If this is a concern, you can ask your birth team which formulation they carry.
Why Newborns Need Vitamin K
Vitamin K is essential for blood clotting. It activates several clotting factors in the liver that allow blood to form clots and stop bleeding. Without enough vitamin K, even a minor bump or normal internal pressure can cause dangerous, uncontrolled bleeding.
Babies are born with very little vitamin K in their systems. It doesn’t cross the placenta efficiently, and breast milk contains only small amounts. This leaves newborns vulnerable to a condition called vitamin K deficiency bleeding (VKDB), which comes in three forms based on timing:
- Early-onset (within 24 hours of birth): Severe, and most common in babies whose mothers took certain medications during pregnancy, such as seizure drugs, that interfere with vitamin K.
- Classical (2 days to 1 week): Causes bruising and bleeding from the umbilical cord stump.
- Late-onset (1 week to 6 months, most often at 2 to 8 weeks): The most dangerous form. Between 30% and 60% of affected infants experience bleeding within the brain. Warning signs before a serious bleed are rare, meaning it often strikes without obvious early symptoms.
Without the shot, early and classical VKDB occurs in roughly 0.25% to 1.7% of births. Late VKDB occurs at a rate of about 4.4 to 7.2 per 100,000 infants. Babies who skip the injection are an estimated 81 times more likely to develop late VKDB than those who receive it.
Side Effects of the Shot
The side effects are essentially the same as any intramuscular injection in an infant: brief pain, possible bruising, or mild swelling at the injection site. A small number of cases of skin scarring at the injection site have been reported. Only a single case of an allergic reaction in an infant has ever been documented, making that outcome extremely rare.
Why an Injection Instead of Oral Drops
There is no licensed oral vitamin K product for newborns in the United States. Some providers have given the injectable liquid by mouth, but this is an unstudied approach with no formal safety or effectiveness data.
Countries that have adopted oral vitamin K programs offer a useful comparison, and the results consistently favor injection. In Switzerland, a two-dose oral regimen (given on day 1 and day 4) still saw late VKDB at a rate of 3.79 per 100,000 births. Adding a third dose at four weeks brought the rate down to 0.87 per 100,000, a significant improvement but still not zero. In the Netherlands, a daily oral regimen of 150 micrograms for three months reduced confirmed late VKDB to 1.8 per 100,000, still considerably higher than the near-zero rate seen with a single injection. No failures have been reported with the intramuscular shot.
Two factors consistently undermine oral regimens: uneven absorption in a newborn’s gut and the challenge of parents remembering to give every dose on schedule over weeks or months. A single injection at birth sidesteps both problems. The American Academy of Pediatrics recommends the intramuscular injection as the standard of care for all newborns.