I have 2 cats, both are almost 2 years old--and they are throwing up hairballs all the time. Occasionally they throw up mostly bile with just a little bit of hair that hasn't clumped. This has been going on for a little over a month. It is happening much more with one cat than the other (I think the cat that isn't throwing up as much is having a regular amount of hairballs like 2/week). I've taken them both to the vet recently when it first started and they can find nothing wrong. They are both alert and active. They are on different foods because one of them had a urinary tract blockage about 6 months ago and has been on a prescription diet ever since. But the vomiting only started in the past month or so. I have no idea what I can do to fix it. I can't give the one cat food to prevent hairballs because he is supposed to be on the urinary food. the other one is already on a food that claims to prevent hairballs. I'm cleaning up bile and hairballs usually twice a day between the both of them. One of them just vomited bile on my stereo.