Hairball Relief Plus Cats is not known to have any side effects if given as per the prescribed dosage.

Hairballs (trichobezoars) are balls of hair that end up in a cat's stomach when the cat licks its fur as part of its regular grooming routine. Since cats spend about 10% of their waking hours grooming themselves primarily by licking their fur clean, hairballs in cats can be a very common occurrence. Many cats have no problem with hairballs whatsoever.

Sometimes though, especially in long-haired cats, hairballs can cause your cat to engage in gagging or retching in an attempt to vomit up the hairball. The cat may or may not actually vomit. On occasion you can actually see the balls of hair in the vomit, but sometimes the hairball will just upset the stomach and the cat will bring up food or liquid and not the hairball itself.

Occasional hairball episodes (1-4 times a month) are normal for most cats and usually prevention is the best treatment. If your cat is vomiting more than this, or if the cat recently starting vomiting more than usual or the cat is vomiting repeatedly, then this can be a sign of a completely unrelated medical problem and the cat should see a vet. In fact the individual cat owner should bring their cat to a vet whenever their cat exhibits unusual behavior that involves vomiting.