Onsior for Cats: Uses, Dosage, and Side Effects

PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.  

What Is Onsior Used for in Cats?

Onsior (robenacoxib) is a prescription nonsteroidal anti-inflammatory drug (NSAID) used in cats to control short-term postoperative pain and inflammation. It’s available as a ​flavored ​oral tablet or an injectable formulation administered by a veterinarian​ on the day of your cat’s surgery​. 

Is Onsior FDA-Approved for Cats? 

Yes​,​ Onsior is FDA-approved for use in cats to control pain and inflammation after orthopedic ​​​surgery​, ​​​spay​, and ​​​neuter​ procedures. 

​​It is approved for cats 4 months of age and older. The oral tablets are labeled for cats weighing more than 5.5 pounds and are given once daily for a maximum of three consecutive days, as directed by a veterinarian.​​     ​ 

In some cases, veterinarians may prescribe Onsior for uses not listed on the drug label. This is called extra-label or off-label use, and your veterinarian will determine whether it’s appropriate for your cat. 

Speak with your veterinarian about whether Onsior is right for your cat. 

Onsior Considerations for Cats

Onsior may not be appropriate for all cats. Your veterinarian will decide if it’s safe based on your cat’s health history and current medications. 

Extra caution may be needed for cats who: 

• Have ​​​kidney​, ​​​liver​, or ​​​gastrointestinal disease​ 

• Are ​​​dehydrated​ or critically ill 

• Are ​​​pregnant​ or nursing 

• Are taking other NSAIDs or corticosteroids 

Older cats or cats with underlying health conditions may need closer monitoring.  

​​Before starting Onsior, a​lways tell your veterinarian about all medications and supplements your cat is taking​.​​     ​ 

How Does Onsior Work in Cats?

Onsior reduces pain and swelling by limiting the chemical ​messengers ​that cause inflammation, especially after surgery. It helps cats feel more comfortable when given exactly as prescribed and for the recommended length of time. 

How To Give Onsior to Cats

Follow the directions on the drug label or as provided by your veterinarian. 

• Onsior is usually first given as an injection by a veterinarian around the time of surgery. 

• If additional doses are needed, it may be given once daily as an oral tablet, with or without food. 

• Tablet and injectable doses are different and should not be substituted without veterinary guidance. 

• Onsior is approved for use in cats for up to three consecutive days. 

• Do not give Onsior with other NSAIDs or corticosteroids unless directed by your veterinarian. 

What Happens If You Miss a Dose of Onsior? 

Speak with your veterinarian about what to do if you forget to give a dose of Onsior. In general, your vet may recommend giving the dose when you remember unless it is close to the time for the next scheduled dose. 

Because Onsior is given once daily for a maximum of three days, your veterinarian may advise skipping the missed dose rather than adjusting the schedule. 

Do not give extra or double doses. 

​Possible Side Effects of Onsior in Cats​​​​​​​​​

​​The most common side effects of Onsior include digestive upset:​ 

• ​​​​Vomiting​ 

• ​​​​Diarrhea​ 

• ​​​​​Decreased appetite​​​​ 

​​Less commonly, serious side effects can occur, including:​ 

• ​​​​Blood in the stool​ or ​​​vomit​ 

• Dark or tarry stool 

• ​​​​Weight loss​ 

• Kidney injury 

When Onsior is given after surgery, some symptoms may be related to the procedure itself rather than the medication, including: 

• Bleeding from the incision site 

• Irritation or infection at the incision site 

• Increased bruising 

Human Side Effects 

​​​Onsior is a prescription veterinary medication not intended for use in humans. Due to possible side effects, humans should never use medicine dispensed for their pets and pets should not be given any medicine dispensed for a human’s use.​​​​​​     ​​ 

If you accidentally ingest a pet medication, seek medical attention in person or call Poison Control at 800-222-1222. 

Monitoring Your Pet 

Your veterinarian may recommend specific monitoring or routine testing while your cat is on this medication depending on your cat’s individual needs, other medications they may be on, and/or the issue that initially caused your cat to be placed on this medication. 

​​​When To Call Your Vet 

Call your veterinarian if you see any of the following, or if you have additional questions or concerns about the use of Onsior: 

• Severe side effects (above) 

• Your pet’s condition worsens or does not improve with treatment 

• You see or suspect an overdose 

What Happens If a Cat Overdoses on Onsior?

​​An overdose of Onsior can cause toxicity affecting the gastrointestinal tract, kidneys, and liver, similar to other NSAIDs.​​     ​​     ​ 

​​Possible signs of an overdose ​include:  

• Vomiting 

• Lethargy 

• Diarrhea 

• Loss of appetite 

• Blood in the vomit or feces 

• Dark or coffee-ground stool 

• ​​​​Increased thirst​ or ​​​urination​ 

• ​​​​Bloody urine​ 

If you suspect an overdose, immediately seek emergency veterinary care or contact an animal poison control center. Consultation fees often apply. 

• Pet Poison Helpline 855-764-7661  

• ASPCA Animal Poison Control 888-426-4435  

How To Store Onsior for Cats

Keep the following storage tips in mind for this medication: 

• Store Onsior tablets at controlled room temperatures between 59–77 F (15–25 C). 

• Always confirm storage temperatures by reading the label.  

• Keep the container tightly closed to protect from moisture and light. 

• Keep out of reach of children and pets.