Can breast milk and formula be mixed?

you can, even though it is not really recommended, unless you have very low breast milk supply. be assured that it will not cause any harm to your baby. it is strongly recommended that you feed your baby only breastmilk till the age of 6 months, post which you can start introducing formula. here are 2 articles you can find useful: https://www.nct.org.uk/parenting/mixed-feeding-combining-breast-and-bottle-feeding https://www.foodsafety.gov/keep/types/babyfood/