This is just a theory but my cat believes that cider is slightly acidic whereas most alcoholic beverages are basic. Again this is based on a very limited understanding of chemistry. Perhaps taking a tums would cure your friends problems.
Also, as a general safety rule here in the forums we don't usually talk about ourselves even when we speak of drugs
that may be legal in our country. Just make sure its clear that your friend drinks cider and not you yourself. It's just a precaution. For instance I'm here to discuss my cat's drug
problems. Personally, I think marijuana
and all other drugs are deplorable but I've learned a bit about them in trying to dissuade my cat.
Welcome to the forums by the way.
Oh, actually my cat just told me that as a youngling he and his friends used to consume hot dog rolls to coat their stomachs. Don't know if this would help in your friends case.