Be sure kitty doesn't have a stomach infection or gastritis. Akira was recently diagnosed with that and she can't ever eat Natural Balance (LID) dry food ever again and was put on antibiotics for two weeks. She is fine now. The antibiotics started helping almost right away, because her breath improved greatly. So, now, it's strictly canned Wellness grain free. She does very well on that. The vet also had me start giving Akira salmon oil for constipation and hair balls. If you can't get animal grade salmon oil, she said it's fine to give human grade salmon oil. The dosage is 1/4 teaspoon per day for cats. You just keep it in the refrigerator. Anyway, this is a nutritional approach to a very common cat problem.
i always fed my cat iams hairball control and there is also a tube of cat laxative that i get from the vet. you squeeze out about an inch long amount every day or 2 and it keeps him from coughing up hairballs. it worked great for my cat i hope it works for yours too.