Robenacoxib (brand name Onsior) is a prescription pain reliever and anti‑inflammatory for cats. It’s a COX‑2 selective NSAID used short‑term to help control pain and swelling after surgery.
Commonly prescribed for: 1) after spay/neuter, and 2) after orthopedic (bone/joint) surgery. Species: cats only. Status: prescription (Rx‑only). Your veterinarian can discuss how long it should be given and what to watch for at home.
If an owner reports vomiting, diarrhea, not eating, unusual tiredness, changes in drinking or urination, or stool color changes while a cat is on Onsior, advise a same‑day call or visit. If symptoms are severe (e.g., repeated vomiting, collapse), direct them to an emergency clinic right away.
Front desk script: Onsior is the brand name for robenacoxib, a prescription pain and anti‑inflammatory medicine for cats. Vets use it short‑term after surgeries like spays/neuters or orthopedic procedures to keep cats comfortable. If your cat on Onsior isn’t eating, is vomiting or has very dark or bloody stool, seems very lethargic, or is drinking/urinating more, please call us today—if severe, go to the ER. Your veterinarian can tell you exactly how long to give it and what side effects to watch for.
Common owner questions and quick answers:
- What is Onsior and what is it for? It’s a prescription anti‑inflammatory pain medicine for cats used to control pain and swelling after surgery. It is intended for short‑term use only; your veterinarian will specify the length of treatment. Do not crush or split the tablets, and follow the label directions your veterinarian provided. Onsior can be given with or without food. Your veterinarian can discuss the specific plan for your cat. [Sources]
- Can I use Onsior with other medications? Do not give Onsior with any other anti‑inflammatory medications (like aspirin or meloxicam) or with steroids (like prednisone). Always tell us about all medicines and supplements your cat is getting so the veterinarian can check for interactions. [Sources]
- What side effects should I watch for? Possible side effects include decreased appetite, vomiting, diarrhea or dark/tarry stool, changes in drinking or urination, or behavior changes (depression/restlessness). Stop the medication and call us the same day if you see these. If your cat has facial swelling, trouble breathing, collapses, or vomits blood/has black stools, seek emergency care immediately. Your veterinarian can advise on next steps and monitoring. [Sources]
- Is there a generic? Yes. As of January 9, 2026, the FDA approved the first generic robenacoxib tablets for cats. Your veterinarian or pharmacy can advise whether brand (Onsior) or a generic version will be dispensed for your cat. [Sources]
Front desk script: Onsior is a short‑term pain reliever for cats after surgery. It can be given with or without food—please follow your prescription label, don’t split the tablets, and use only as directed by the veterinarian. Don’t combine it with other pain meds or steroids unless our veterinarian has specifically said to do so. If you see vomiting, diarrhea, less appetite, dark stools, or changes in drinking or urination, stop the medication and call us today; for facial swelling, trouble breathing, collapse, or blood in vomit/stool, go to the nearest emergency clinic now. If a dose is missed or your cat spits it out, don’t double up—call us and we’ll guide you.
What owners most often report in the first 1–3 days on Onsior (robenacoxib) for cats are mild stomach/intestinal signs: a single episode of vomiting, softer stool, slightly decreased appetite the day of or after surgery, and sleepiness. If an Onsior injection was also given in the clinic, brief soreness or a small lump at the injection site can occur. These effects are typically short-lived; advise owners to monitor appetite and demeanor closely. Manufacturer and FDA materials list the most common tablet-related effects as decreased appetite, lethargy/depression, vomiting, and—less commonly—kidney-related lab changes or kidney issues. Incision-site bleeding or infection has also been reported postoperatively. [Your veterinarian can discuss individual risk and any monitoring plans.]
Have owners call the clinic the same day if diarrhea or vomiting is more than a single, mild episode; if the cat won’t eat by the next day; or if there’s any increased drinking/urination or very little urine. Escalate immediately if there is blood in vomit or stool, black/tarry stool, yellow gums/eyes, severe lethargy, collapse, wobbliness, seizures, or a hot, painful, or draining injection-site swelling; these can signal serious NSAID or post-op complications and need urgent veterinary assessment. FDA and manufacturer guidance stress contacting the veterinarian promptly if side effects are suspected and not using Onsior with other NSAIDs or steroids; any decisions about continuing or adjusting medication must be made by the veterinarian.
Front desk script: Thanks for calling about your cat on Onsior—some cats have a one‑time vomit, softer stool, or seem sleepy the day after surgery, which can be expected. Because you’re seeing [summarize concern], I’d like to alert our veterinarian and get guidance for you. If your cat vomits more than once, won’t eat by tomorrow, has black or bloody stool or vomit, seems very weak or wobbly, shows yellow gums, or has a hot, painful swelling, please seek urgent care right away and let us know. Your veterinarian will advise you on next steps and whether any testing or medication changes are needed.
Forms and how to give: Onsior for Cats is dispensed as a small oral tablet for at‑home use; a veterinary injection may also be used by the clinic around surgery time. Give tablets whole; they are not designed to be split, crushed, or chewed. It may be given with or without food, but a full meal can reduce how much is absorbed—many clinics suggest offering it on an empty stomach when possible; a small bite or treat is okay if needed. If pilling is hard, try a cat pill pocket or soft treat, a tiny gelatin capsule, a pill‑giver device, or a quick swallow followed by a small amount of water or a soft treat to help it go down. Your veterinarian can discuss alternatives if tablets are not possible for your cat.
Troubleshooting: If your cat vomits right after a dose or you aren’t sure the pill was swallowed, call the clinic before repeating any dose—do not double up unless the veterinarian directs you. For missed doses or if food was given at the same time, the veterinarian can advise the best next step. If hiding in food, avoid mixing the tablet into a full meal; use only a small bite so you can confirm the dose was taken.
When to escalate: Vomiting that happens more than once, black or tarry stools, blood in vomit, yellow gums/eyes, marked drop in appetite, changes in drinking or urination, or unusual lethargy or wobbliness are concerning with any NSAID. This is urgent—contact the veterinarian immediately or seek emergency care. Your veterinarian can also advise whether a legally compounded flavored liquid is appropriate when tablets cannot be given; note that compounded products are not FDA‑approved and can vary in quality, so they should only be used under veterinary direction.
Front desk script: Onsior tablets should be given whole. It can be given with or without food, but a full meal can lessen absorption—try a small bite or treat if needed. If your cat vomits after a dose or you’re unsure it was swallowed, please call us before giving another dose. If you see repeated vomiting, black or bloody stool or vomit, yellow gums, very low appetite, or changes in urination or drinking, this is urgent—contact us right away or go to emergency care. If pilling is a struggle, we can ask the veterinarian about alternatives, including whether a legally compounded liquid would be appropriate for your cat.
Onsior (robenacoxib) is an Rx-only NSAID for cats that is labeled for short-term postoperative pain control for up to three days. Because it is intended for brief use, refills are uncommon and must be reviewed by a veterinarian; continued pain after surgery or any request to extend therapy requires veterinarian approval and may require a recheck exam. A valid prescription under a veterinarian’s supervision is required, and owners must receive the FDA “Client Information Sheet” with NSAIDs. Your veterinarian can discuss if a re-exam, bloodwork, or alternative pain plan is needed.
Refill call checklist: confirm pet and owner, medication name, surgery/reason and surgery date, last dose given, current signs (especially vomiting, diarrhea, black/tarry stool, not eating, lethargy, changes in drinking/urination, or yellow gums/eyes), and all other meds (flag any NSAID or steroid use). Standard turnaround for non-urgent refills is 1–2 business days; same-day prioritization is reasonable for recent discharges with missing doses. If concerning signs are reported, escalate to a veterinarian immediately; severe signs (collapse, severe trouble breathing, black/bloody stool) warrant emergency referral.
Online pharmacy process: prescriptions can be filled in-clinic or sent to a licensed pharmacy. Verify the exact product requested is the cat-labeled robenacoxib (Onsior or an FDA‑approved generic for cats); dog-labeled products or compounded versions require explicit veterinarian approval. Provide the pharmacy name, phone/fax, and email; the veterinarian will approve or modify the request and ensure the NSAID Client Information Sheet is provided.
Front desk script: Thanks for calling about an Onsior refill. This medication is labeled for short-term use after surgery, so most refills need a veterinarian’s review and sometimes a recheck—let me gather a few details and I’ll send this to the doctor. Can you confirm your cat’s name, the surgery/reason and date, the last dose given, any other meds, and whether you’ve noticed vomiting, diarrhea, black stools, not eating, lethargy, or changes in drinking/urination? Our usual turnaround is 1–2 business days; tell me if you need it sooner. If you prefer an outside pharmacy, we can send a prescription to a licensed pharmacy for the cat-labeled robenacoxib once the veterinarian approves. If you’re seeing severe signs like collapse, trouble breathing, or black/bloody stool, please go to the nearest emergency clinic now and I’ll alert our veterinarian.
Emergency red flags while a cat is on Onsior (robenacoxib): vomiting or diarrhea with blood, black/tarry stool, "coffee‑ground" vomit, very pale gums, sudden collapse, seizures, severe weakness, trouble breathing, or facial/neck swelling or hives (possible allergic reaction). Little or no urination, marked increase in drinking/urination, or yellow gums/eyes can indicate kidney or liver problems. If any of these are reported, stop the conversation and get a veterinarian or technician immediately; advise the caller to come in now or go to the nearest emergency clinic. Your veterinarian can discuss next steps and monitoring.
Overdose or interaction red flags: the cat was given an extra dose, a dose meant for a dog, another pain/anti‑inflammatory or steroid on the same days (for example, aspirin, meloxicam, carprofen, prednisone), or Onsior has been given longer than prescribed (more than the label’s short, 3‑day maximum). Also escalate promptly if the cat isn’t eating, is repeatedly vomiting, is very lethargic, or has pre‑existing kidney/liver disease and now seems unwell. These situations can be serious—loop in a vet/tech right away for instructions.
Front desk script: Thanks for calling—because you’re seeing those signs while your cat is on Onsior, I’m getting our veterinarian or technician on the line right now. If your cat has bloody or black stool, is vomiting blood, has facial swelling or trouble breathing, or has collapsed, please come to the clinic immediately or head to the nearest 24‑hour ER. If there was an extra dose or any other pain or steroid medicine was also given, that needs urgent veterinary guidance—I’ll connect you now. Please bring the Onsior packaging and any other medications with you.
Key interaction flags for Onsior (robenacoxib) in cats: do not combine with any other NSAID (e.g., aspirin, meloxicam) or with corticosteroids (e.g., prednisone), as this raises the risk of stomach/intestinal bleeding and kidney problems. Extra caution is needed if an owner reports diuretics (e.g., furosemide) or dehydration, because NSAIDs plus diuretics can stress kidney function. Robenacoxib is highly protein‑bound and may interact with other highly protein‑bound medicines; the label advises monitoring when other drugs are on board. It may also prolong the QT interval, so concurrent QT‑prolonging drugs (some antihistamines or pro‑kinetics) should be flagged for veterinarian review. If an owner mentions black/tarry stool, vomiting blood, severe vomiting/diarrhea, marked lethargy, collapse, trouble breathing, or no urine—escalate immediately. Your veterinarian can discuss risks and the plan if other meds are present. [Label and FDA NSAID guidance]
Front desk script: Thanks for letting us know about the other medication. Because your cat is on Onsior, we need our veterinarian to review any other meds—especially steroids, other pain relievers, or diuretics—to be sure they’re safe together. Please do not give any human pain medications (Tylenol, ibuprofen, naproxen, or aspirin). If you’ve already given one, or if you see black stools, vomiting blood, severe vomiting/diarrhea, trouble breathing, or your cat isn’t urinating, go to the nearest emergency vet now and call us on the way.
Store Onsior (robenacoxib) 6 mg tablets for cats at controlled room temperature, 59–77°F (15–25°C). Keep tablets in their original labeled blister card and dispensing envelope; do not repackage. The tablets are not scored and should not be split or crushed. Always store out of reach of children and all pets, as flavored tablets can be attractive if left out. Your veterinarian can discuss secure storage options for homes with curious pets or young children.
Shelf life: there is no special “after opening” time limit for the blister‑packed tablets—use by the expiration date on the package. For disposal, prefer a drug take‑back program or return to the clinic if offered. If no take‑back is available and the medicine is not on FDA’s flush list, mix unused tablets (do not crush) with an unappealing material like used coffee grounds or cat litter, seal in a bag, and place in household trash. Do not flush unless specifically recommended by FDA’s flush list. If you have disposal questions, your veterinarian can advise what’s allowed locally.
Escalation: if anyone (including another pet) swallows tablets not prescribed for them, or if the cat consumes more than directed, treat as urgent—contact the clinic immediately. If a person ingests Onsior, seek medical advice/Poison Control right away.
Onsior for Cats is typically prescribed short term after surgery (up to 3 days). For scheduling, book the surgeon’s routine post‑op check per the doctor’s plan; a separate “Onsior‑only” recheck isn’t usually needed for such a short course unless the veterinarian requests it. When dispensing, record the start date on the envelope and remind owners that our team will review how their cat is doing at the post‑op visit.
Before any NSAID is started, the product label advises a complete history and exam, with appropriate baseline lab tests to document blood values; your veterinarian will determine if and when these tests are needed. Additional check‑ins or lab rechecks are at the veterinarian’s discretion, especially for cats with kidney, liver, or bleeding concerns. Please defer any questions about test timing or frequency to the doctor.
Escalate urgently if owners report red‑flag signs during the Onsior course or soon after surgery: vomiting, diarrhea, not eating, black or bloody stool, unusual bruising/bleeding, marked lethargy, yellow gums/eyes, or changes in drinking or urination. Schedule a same‑day exam and alert a veterinarian; the veterinarian will advise on next steps, including any medication or testing changes.
Front desk script: “Onsior is a short‑term pain and anti‑inflammatory medication used after surgery. The doctor may want baseline bloodwork before the first dose—I can schedule that with your pre‑op or discharge as directed by the veterinarian. While your cat is on Onsior, please watch for vomiting, not eating, black or bloody stool, unusual sleepiness, or changes in drinking or urination. If you notice any of these, please call us right away so our veterinarian can advise you and we can arrange a same‑day visit if needed.”
Onsior (robenacoxib) is a prescription NSAID for cats used to control pain and inflammation after surgery (spay/neuter or orthopedic). Per the FDA‑approved label, it’s for cats 4 months of age and older that weigh at least 5.5 lb, and it is used short‑term for up to a maximum of 3 days. Your veterinarian can discuss if/when it’s appropriate for an individual cat and how it should be given.
Safety reminders for front desk: direct owners to speak with the veterinarian before combining Onsior with any other pain medicines or steroids. Possible side effects can include decreased appetite, vomiting, diarrhea, changes in stool color, changes in drinking or urination, or lethargy. If a caller reports repeated vomiting, black/tarry or bloody stool, not eating, severe weakness/collapse, or yellow gums/eyes, escalate the call to a veterinarian immediately; if we are closed, direct them to the nearest emergency clinic.
Phrases to avoid: “It’s safe for all cats,” “Just give another dose,” “Go ahead and stop/start it,” “You can split the tablet,” or “It’s fine to use with other pain meds.” Instead, defer dosing and medical decisions to the veterinarian.
Front desk script: Thank you for calling [Hospital Name], this is [Your Name]. Onsior is a prescription pain and anti‑inflammatory medicine for cats used short‑term after surgery—your veterinarian will advise exactly how to use it. If your cat is vomiting, has black or bloody stool, won’t eat, seems very weak, or you notice yellow gums or eyes, please tell me now—this may be urgent, and if we’re closed, please go to the nearest emergency clinic. For dosing, drug interactions, or side‑effect questions, let me connect you with our veterinarian or nurse. I can also arrange a same‑day call‑back or schedule a recheck—what works best for you?