Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Not for babies with gas or colic

I was very disappointed with the Avent system. We had my son on the bottles for almost 3 months. He had constant gas and colic which was very painful for him. At first we thought it was the formula; then by process of elimination we realized it was the bottles. We frequently upgraded on the nipple size up to stage 4- which became very pricey. He became so frustrated that he only ate in small amounts (1-2 ounces). After a recommendation from a friend we switched to Dr. Brown's. He is now eating normal amounts and is not gassy.