Psyllium fiber (Metamucil, or generic) has been proven safe in cats. Smudge gets it twice daily and is much more comfortable than he used to be.

Some cats also enjoy canned pumpkin, either mixed with canned food or just plain!

Vaseline (and treats like Temptations that contain petroleum jelly) aren't always indicated because they prevent cats from being able to absorb all the nutrients they need from their food.

Love, Columbine