I'll echo others that, if you can, continue to breastfeed and/or pump and offer expressed breastmilk. Only your breastmilk can change in its composition of carbohydrates, fats and proteins to meet your child's continuing developmental and nutritional needs. Formula cannot and will not ever be able to do that; so, if you are able, continue to offer what is best - your milk. Also, 5 mos is pretty late in the game to try to introduce a bottle to an exclusively breastfed baby. My now 11 mos old refused the bottle for 3 solid weeks after I returned to work (where I pumped milk for him), even though we had introduced the bottle to him at 3 weeks old and gave it to him occasionally before I returned to work when he was 6 mos old. If you can, have another person offer the bottle. If he can smell your milk, he for sure won't take it from you. My son eventually took the Playtex nurser. Look at your nipple and the nipple on the bottle. Try to find one that is closest to what your baby is familiar with. And also try silicone and, oh, I can't remember the other material nipples are made out of, but, check the packaging and make sure you offer the alternative if you haven't already. Your baby may prefer one over the other.