Pacifier use is one of the more controversial issues in breastfeeding and in parenting in general (there are many such areas unfortunately). Current guidelines suggest avoiding pacifiers until breastfeeding is well established at 3-4 weeks of age. Current guidelines also suggest that pacifiers can help reduce the risk of SIDS, but if breastfeeding, wait until 3-4 weeks of age (thankfully, a unified message). The U.S. version of the Baby-Friendly Hospital Initiative bans hospitals from providing pacifiers to parents and the routine use of them in the hospital because of concerns that they may interfere with breastfeeding (although there is no scientific evidence that they do).
What does research (and experience) show?
Pacifiers are generally acceptable and seldom interfere with breastfeeding.
Pacifiers are unlikely to cause nipple confusion or interfere with breastfeeding that way. If a baby is hungry and needs to eat and a pacifier is used instead of feeding the baby, this can cause the baby to be underfed and even become dehydrated. If you are sure the baby is fed, you can use a pacifier to help your baby calm down.
A systematic review of published studies (there are not many) showed that pacifier use did not affect breastfeeding rates at 4 months of age. However, the women in these studies were highly motivated to breastfeed. It is unknown what effect pacifiers have on breastfeeding in moms who are not as motivated.
There are some studies that suggest that pacifiers are associated with decreased breastfeeding rates. However, these studies cannot tell whether it is coincidence or which is the cause. It may be that mothers who are struggling with breastfeeding (and more likely to fail) are more likely to use a pacifier due to a fussier baby, rather than the use of a pacifier causing breastfeeding problems. In this case, pacifier use would be a marker, not a cause, of breastfeeding problems. (This is a fundamental principle of medical research: association or correlation is not the same thing as cause. The media, and many doctors, do not always understand this).
You may find that your birth hospital may not give you a pacifier and you have to supply it yourself. This is particularly true if the hospital is certified as a Baby Friendly Hospital, where it must be against hospital policy to provide pacifiers.
Many breastfeeding experts feel that pacifiers should be avoided, but honestly I have not seen many babies have a problem nursing due to pacifier use; I have seen many lazy nursers due to bottle feeding during the first 2 weeks of life. Overall, it is probably best to avoid pacifiers if possible the first 2-3 weeks and feed your baby instead, but it is acceptable to use one if it is helpful and you are sure your baby is well fed.
References
Psaila K, Foster JP, Pulbrook N, Jeffery HE. Infant pacifiers for reduction in risk of sudden infant death syndrome. Cochrane Database of Systematic Reviews. 2017;(4). doi:10.1002/14651858.CD011147.pub2
Jaafar SH, Ho JJ, Jahanfar S, Angolkar M. Effect of restricted pacifier use in breastfeeding term infants for increasing duration of breastfeeding. Cochrane Database of Systematic Reviews. 2016;(8). doi:10.1002/14651858.CD007202.pub4
Moon RY. SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment: Policy Statement. Pediatrics. 2011;128(5):1030-1039. doi:10.1542/peds.2011-2284
Moon RY, Syndrome TF on SID. SIDS and Other Sleep-Related Infant Deaths: Evidence Base for 2016 Updated Recommendations for a Safe Infant Sleeping Environment. Pediatrics. 2016;138(5):e20162940. doi:10.1542/peds.2016-2940
Eidelman AI, Schanler RJ, Johnston M, et al. Breastfeeding and the Use of Human Milk. Pediatrics. 2012;129(3):e827-e841. doi:10.1542/peds.2011-3552
Jaafar SH, Jahanfar S, Angolkar M, Ho JJ. Effect of restricted pacifier use in breastfeeding term infants for increasing duration of breastfeeding. Cochrane Database of Systematic Reviews 2012, Issue 7. Art. No.: CD007202. DOI: 10.1002/14651858.CD007202.pub3