Why has my baby stopped drinking milk?

Did you change the nipple size

How long has it been going on? He could just not be in the mood for it or it’s upsetting him, so he doesn’t finish it. My daughter did this a few times here and there. If it’s only been a couple of times, wait maybe one or two more times the make an appointment with the doctor. It could be nothing, but you want to check with their Dr to confirm

Change the nipple size up!
What bottle are you using?
Try to use a Philip Advent bottle (glass ones), these nipples are really good as the milk only comes out when sucked.
My girl was the same way, and we switched to a size 2 with the Philp Advent bottles, and she is drinking normally again.

Try the teat size up and if it continues try a different brand; also maybe shift feeding times slightly, different environment (calm / dark / quiet) and sitting him up more while feeding to pace feed x

My son is like this. He'll guzzle it during a growth spurt and then afterwards back to having small amounts. Just follow her lead. If he's in discomfort then see a HV or GP. They'll weigh him and see how he's progressing.

Before that try changing teat sizes if you haven't already. That helped my son drink a bit more.

I'd contact his pediatrician ASAP.

If it seems he’s having difficulty eating but seems hungry it might be something physical, I’d check inside the mouth if there’s white patches on the gums, inside of the mouth or tongue it might be oral thrush, which is totally normal for newborns, he would just need medicine. But if nothings there it might just be the nipple on the bottle and or a switch up of when he’s feeling hungry. Hope all goes well!