I have read, more, than a few posts on catsfur, that say, not to give it. Something about it coats the intestines, and prevents absorbtion of the nutrients, or something, like that. The others might be able to give you a better explanation.
If the issue is hairballs, I use Petromalt. They lick it right off my fingers, the kittens even fistfight, about who's
turn it is, mol. If the issue is constipation, yrs ago, when one had it, my vet said to give Metamucil, its a powder, you give 1/4 teaspoon, once a day, mixed with wet food, or baby food. It has to be sugar free and unflavored. One thing, I can guarantee, will move things along, is give them a whole jar of baby food. Made that mistake at one show, forgot his food, at the show hotel, and thats all I had to give him, the next morn, he had diarea, had to wash his bee-hind in the hotel sink, mol.