Best hairball remedy for cats?

I have 2 – 11 year old Ragdoll cats (long haired). Lately, my boy has been throwing up a lot and I think it’s being caused by hairballs. The vet had recommended some medication they sell but I wanted to get some of your opinions on which products work best. My boy is allergic to a lot of things, so most treats for him will not work.

What have you tried that has work, or hasn’t worked?