My daughter has been on Zantac since she was about 1 month old. Before the Zantac, she was always fussy, it seemed like she was never comfortable, and she was spitting up ALL THE TIME. She was sleeping ok, but would wake up with sudden stomach pain and just start SCREAMING. We finally figured out that she has acid reflux. We also found out that she was allergic to Mylicon which was HORRIBLE!! But Zantac is prescribed to stop the burning and pain in the stomach and throat, not for spit up. She is 5 months old now, and she is pretty much always happy, still spits up of course, but i can tell she feels much better, and sleeps thru the night. Actually, after about the first week of giving the meds to her, she started sleeping thru the night. Another reason why i think it is working so well, when i run out of it, and the pharmacy is closed for the weekend, ALL weekend she is horrible, really fussy, cant sleep and screams every time she spits up. As soon as i get the med and start giving it to her, she is better. She does fight sleep alot, but i dont think that has anything to do with the Zantac. I am in the process of trying to find a formula that helps with the spit up tho. I have tried Similac(blue can) Similac Sensitive(orange) Enfimil(regular) Enfimil Sensitive and i am about to try Parents Choice. I guess we'll see. I hope this information has helped you.