throwing up/ dry heaving constantly right after drinking

My friend sometimes gets very sick right after drinking. I understand throwing up after getting drunk is normal but the extant that they do doesn’t seem normal.

To explain, when this happens it’s not like they get extremely drunk but I guess that is dependent on the person. They seem to just tip over their limit and start throwing up. Once they start though, they can’t stop for hours. They will just feel extremely nauseous all throughout the night and constantly throw up even when there is nothing to throw up. We try the normal things to help a hangover like drinking water and eating crackers but that is almost impossible. Most of the time spent throwing up they don’t even show any other signs of being drunk other than being nauseous. Eventually it passes but still it doesn’t seem normal.

I want to know if anyone has any info on this. Is this normal? Is this caused by some weird medical thing because they are small and possibly anemic? Is there anything to do to help/prevent this other than just not drinking?