# What Are the Side Effects of Apoquel for Cats?


## Key Takeaways

- Apoquel (ocitinib) is an off-label medication for cats used to block itch signals, primarily for allergic skin disease, by inhibiting Janus kinase (JAK) pathways involved in inflammation.
- Common side effects in cats are mild gastrointestinal upset (vomiting, reduced appetite) and transient drowsiness, typically resolving within a few days.
- A significant risk associated with Apoquel is immune system suppression, increasing susceptibility to bacterial and fungal skin/ear infections due to overgrowth of normal flora.
- More serious, though less common, side effects include persistent vomiting/diarrhea leading to dehydration, hepatic lipidosis from anorexia, and rare hematological changes (pale gums, bruising).
- Immediate veterinary attention is required for signs of severe allergic reactions (facial swelling, difficulty breathing), collapse, seizures, or uncontrollable vomiting, while less severe but persistent symptoms warrant prompt veterinary consultation.
- Owners must adhere strictly to prescribed dosages and never alter or discontinue Apoquel without veterinary guidance, as abrupt cessation can lead to rebound pruritus and incorrect dosing increases adverse event risk.

---

If your cat has been prescribed Apoquel (the brand name for the drug oclacitinib), you are likely wondering what to expect. Apoquel is a medication that blocks certain itch signals in the body. It is officially approved for dogs with allergic skin disease, but veterinarians sometimes prescribe it for cats as an off-label treatment. Off-label means the drug is not formally approved for cats, but your vet has a medical reason to believe it can help. The most common side effects in cats are mild stomach upset, such as vomiting or reduced appetite, and these often settle within a few days. However, because Apoquel works by calming part of the immune system, it can also make it easier for infections to take hold. You should watch your cat closely for any new signs of illness, especially in the first two weeks of treatment.

Most cats tolerate Apoquel well, but every cat is different. You should never change the dose or stop the medication without talking to your veterinarian first. Stopping suddenly can cause the itching to return quickly, and changing the dose on your own can increase the risk of side effects. Your vet will tell you exactly how much to give and for how long. If you have any doubt about whether a symptom is normal, call your vet's office. They would rather hear from you than have you worry at home.

## Is This an Emergency?

Some side effects are serious and need immediate care. Use this table to decide what to do. If you are ever unsure, treat it as urgent and call your vet or an emergency clinic.


<!-- figure:auto -->
```figure
{
 "type": "triage",
 "title": "Urgency triage by severity of signs",
 "tiers": [
  {
   "tier": "danger",
   "label": "Go to an emergency vet now",
   "signs": [
    "Difficulty breathing, wheezing, or rapid breathing at rest",
    "Swelling of the face, lips, or tongue",
    "Collapse, seizures, or sudden weakness",
    "Vomiting that will not stop, especially with blood"
   ],
   "action": [
    "Do not wait",
    "Do not try home care",
    "Take your cat to the nearest open veterinary emergency facility immediately"
   ]
  },
  {
   "tier": "warn",
   "label": "Book a same-day appointment",
   "signs": [
    "Repeated vomiting (more than twice in 24 hours), diarrhea that lasts more than a day, refusal to eat for more than 24 hours, or a fever (ears and nose feel hot, cat is lethargic and hiding)",
    "New lumps, skin sores, or a sudden increase in scratching"
   ],
   "action": [
    "Call your regular vet as soon as they open",
    "Describe what you have seen and follow their advice for the appointment"
   ]
  },
  {
   "tier": "safe",
   "label": "Watch at home for a defined period",
   "signs": [
    "Mild soft stool for one day, one episode of vomiting, or a slight decrease in appetite for less than 24 hours",
    "Mild drowsiness or a quieter manner for the first day or two of treatment"
   ],
   "action": [
    "Keep giving the medication as prescribed unless your vet says otherwise",
    "Offer small, bland meals",
    "If the sign does not improve within 48 hours, or if it gets worse, call your vet"
   ]
  }
 ]
}
```

| Urgency Level | Signs You Might See | What to Do |
|---|---|---|
| Go to an emergency vet now | Difficulty breathing, wheezing, or rapid breathing at rest. Swelling of the face, lips, or tongue. Collapse, seizures, or sudden weakness. Vomiting that will not stop, especially with blood. Pale or white gums. | Do not wait. Do not try home care. Take your cat to the nearest open veterinary emergency facility immediately. |
| Book a same-day appointment | Repeated vomiting (more than twice in 24 hours), diarrhea that lasts more than a day, refusal to eat for more than 24 hours, or a fever (ears and nose feel hot, cat is lethargic and hiding). New lumps, skin sores, or a sudden increase in scratching. | Call your regular vet as soon as they open. Describe what you have seen and follow their advice for the appointment. |
| Watch at home for a defined period | Mild soft stool for one day, one episode of vomiting, or a slight decrease in appetite for less than 24 hours. Mild drowsiness or a quieter manner for the first day or two of treatment. | Keep giving the medication as prescribed unless your vet says otherwise. Offer small, bland meals. If the sign does not improve within 48 hours, or if it gets worse, call your vet. |

## What Is Apoquel and How Does It Work in Cats?

Apoquel contains oclacitinib, a drug that blocks a specific enzyme (a type of protein) involved in the itch and inflammation pathway. When your cat has allergies, their immune system releases chemicals that cause intense itching. Apoquel interrupts that signal, which is why it can be so effective for allergic skin disease. In cats, it is often used for conditions like flea allergy dermatitis, food allergies, or environmental allergies that cause scratching, hair loss, or skin sores.

Because the drug dampens part of the immune response, it does also stop itching. It also reduces the body's ability to fight off some infections. This is the main reason your vet will want to monitor your cat during treatment. The drug is not a steroid, so it does not cause the excessive thirst and urination that steroids often do. That is one reason some vets prefer it for long-term allergy control.

## Common Side Effects You May Notice

The most frequently reported side effects in cats are digestive. You might see one or two episodes of vomiting, soft stools, or a mild drop in appetite during the first week. These signs are usually short-lived and do not require treatment. Some cats also seem a little sleepy or less playful for the first couple of days. This is not dangerous, but it is worth mentioning to your vet at your next check-in.

Another common effect is an increased susceptibility to skin and ear infections. Because the immune system is slightly suppressed, bacteria and yeast that normally live on the skin can overgrow. Watch for red, moist, or smelly skin, especially in the ears, between the toes, or around the chin. If you see crusty sores, pus, or a strong odor, call your vet. These infections are treatable, but they need attention.

## Less Common but More Serious Side Effects

Some cats develop more serious reactions. These are not common, but they require prompt veterinary care. Watch for persistent vomiting or diarrhea that lasts more than 24 hours, because this can lead to dehydration. A cat that stops eating for more than a day is at risk for a condition called hepatic lipidosis, where the liver becomes overloaded with fat. This is serious and needs treatment.

Apoquel can also rarely cause blood cell changes. Signs of this include pale gums, unusual bruising, small red spots on the skin, or a sudden lack of energy. If you see any of these, your vet will want to run blood tests. Another rare but serious reaction is a severe allergic response, which can cause facial swelling, hives, or difficulty breathing. This is an emergency, as described in the table above.

## What Else Could Be Causing These Signs?

The signs you are seeing may not be from Apoquel at all. Cats hide illness well, and many conditions look alike. For example, vomiting and appetite loss can come from a hairball, a dietary indiscretion (eating something they should not have), or an underlying condition like kidney disease or hyperthyroidism (an overactive thyroid gland). Skin sores could be from a bacterial infection, ringworm, or a flea allergy, not the medication.

This is why your vet will ask about the timing of symptoms. If the signs started right after the first dose, the drug is a likely culprit. If they started weeks later, another cause is more probable. Do not assume the drug is safe or unsafe based on a single symptom. Your vet can run tests, such as blood work or skin scrapings, to find the true cause. The [FDA's guidance on giving pet medication safely](https://www.fda.gov/animal-veterinary/animal-health-literacy/how-give-your-pet-medicine-safely) emphasizes that you should always confirm the correct dose and route with your vet before starting any new drug.

## How to Give Apoquel Safely

Give the medication exactly as your vet prescribed. Do not split pills unless your vet tells you to, and do not hide the pill in a full meal if your cat is a picky eater, because you may not know if they swallowed the whole dose. The [American Veterinary Medical Association's pet owner resources](https://www.avma.org/resources-tools/pet-owners) recommend keeping a log of when you give each dose and any signs you notice. This record is very helpful if your cat has a reaction, because your vet can see the pattern.

If you miss a dose, do not double up. Give the next dose at the regular time and tell your vet at your next visit. If your cat vomits shortly after receiving the pill, call your vet before giving another dose. They may advise you to try again with food or to switch to a different medication. Never give Apoquel with other drugs, including over-the-counter products, without explicit approval from your vet. Drug interactions are possible, and your vet needs to know everything your cat is taking.

## What You Can Do at Home Right Now

If your cat has already taken Apoquel and you are watching for side effects, start with these steps.

Stop the next dose until you speak with your veterinarian. This is not the same as stopping treatment forever. It simply gives you time to report what you see and get advice on whether to continue. If your cat has only mild signs, like slight drowsiness or a softer stool, you do not need to rush to an emergency clinic. Call your regular veterinarian during business hours and describe what happened.

Do not give your cat any other medication to treat a side effect. Do not give human antihistamines, anti-nausea drugs, or pain relievers. Cats process medications very differently from people and from dogs. A dose that seems small can be toxic. Only a veterinarian can choose a safe medication and dose for your cat.

Do not induce vomiting unless a veterinarian tells you to. If your cat vomited after the dose, that is different from you making them vomit. Forcing vomiting at home can cause aspiration, where stomach contents enter the lungs, and that can be life-threatening.

Do not try to hide the tablet in food and assume the problem is solved if your cat eats it. If your cat vomits the pill back up, part of the dose may have been absorbed and part may not have been. Your veterinarian needs to know exactly what happened so they can decide whether a repeat dose is safe.

## What to Write Down Before You Call

A clear timeline helps your veterinarian make a faster and safer decision. Write these things down before you call.

- The exact time you gave the dose.
- The strength of the tablet, if you know it, and what the label says.
- Whether your cat ate a full meal before or after the dose.
- The first time you noticed any change in behavior, appetite, or litter box use.
- How many times your cat vomited or had diarrhea in the past 24 hours.
- Whether your cat is drinking more or less water than usual.
- Whether your cat is urinating more often, straining to urinate, or producing less urine.
- Your cat's temperature, if you can take it safely at home. A normal cat temperature is between 100.5 and 102.5 degrees Fahrenheit. If you do not have a pet thermometer, do not force one. A rectal temperature on a struggling cat can cause injury.
- Your cat's gum color. Lift the lip and look. Healthy gums are pink and moist. Pale, white, blue, or brick-red gums are urgent signs.
- Your cat's breathing rate at rest. Count breaths for 15 seconds and multiply by 4. Normal is roughly 20 to 30 breaths per minute. More than 40 at rest is concerning.

Take a short video of any visible problem. If your cat is wobbling, twitching, scratching, or having trouble walking, record it. A video is often more useful than a verbal description.

## What a Veterinary Visit Usually Involves

Your veterinarian will start with a history. They will ask about the dose, the timing, and every sign you have observed. They will ask about other medications, including flea and worm products, because drug interactions matter.

The physical exam will include taking a temperature, listening to the heart and lungs, feeling the abdomen, checking the lymph nodes, and looking at the skin and ears. These steps cannot be done over video. If your cat has vomiting, diarrhea, or a poor appetite, bloodwork is commonly recommended. A complete blood count checks for infection, anemia, and platelet problems. A chemistry panel checks kidney and liver values and electrolytes. A urine sample checks kidney function and looks for signs of infection.

If your cat has neurological signs, like tremors or seizures, your veterinarian may recommend blood pressure measurement or imaging. If your cat has skin signs, a skin scrape or cytology may be needed to rule out mites or infection.

The cost of a visit depends on what is done. A basic exam and consultation might range from 50 to 150 dollars. Bloodwork adds roughly 100 to 250 dollars. Urinalysis adds about 30 to 80 dollars. Imaging or hospitalization can add several hundred dollars. These are general ranges only. Prices vary widely by region and clinic, and emergency or after-hours fees are higher. Ask for an estimate before tests are run.

## Monitoring Checklist for the Next 48 Hours

Use this table to track your cat after any dose of Apoquel, whether or not you see problems.

| What to Check | How to Check It | What to Write Down |
| --- | --- | --- |
| Appetite | Note if your cat eats within 2 hours of a meal | Amount eaten, or refused |
| Water intake | Note how often your cat drinks in 24 hours | More, less, or unchanged |
| Vomiting | Count episodes in 24 hours | Time of each episode |
| Diarrhea | Check litter box or observe stools | Number, consistency, blood present |
| Urination | Watch litter box use | Frequency, straining, amount |
| Energy level | Compare to normal daytime activity | Lethargic, normal, restless |
| Breathing at rest | Count breaths for 15 seconds, multiply by 4 | Breaths per minute |
| Gum color | Lift lip, look at gums | Pink, pale, red, blue |
| Skin and ears | Look for redness, swelling, or scratching | Location and severity |
| Walking and balance | Watch your cat move across a room | Wobbly, stiff, normal |

If any of these change suddenly, call your veterinarian. If your cat collapses, has a seizure, cannot breathe, or stops urinating entirely, go to an emergency clinic immediately.

## When an Online Vet Can Help, and When It Cannot

Some situations in this article require hands-on care and must not be handled remotely. If your cat has pale or blue gums, difficulty breathing, a seizure, collapse, or is straining to urinate without producing urine, do not use an online consultation. These are emergencies. Go to an in-person emergency clinic now. The same applies if your cat cannot keep water down for more than 12 hours.

A remote consultation is genuinely useful in other situations. If your cat has mild drowsiness after a first dose, a single soft stool, or a question about whether a sign warrants a visit, an online veterinarian can help. They can also help with a recheck on a known problem, a medication side effect question, or a follow-up on a chronic skin condition.

A remote veterinarian can take a detailed history, look at visible signs on video, advise you on whether to continue or pause a medication, and in many states prescribe. What they cannot do is palpate the abdomen, listen to the chest, take a temperature, run bloodwork, or image anything. Those limitations matter. Many signs have several possible causes that cannot be resolved without an examination or testing.

Prescribing rules differ by state. A veterinarian may require an in-person examination before prescribing or continuing Apoquel. That is a legal requirement in many places, not a lack of trust. If an online vet cannot prescribe, they can still tell you whether an in-person visit is needed and how urgent it is.

The [FDA's guidance on giving pet medication safely](https://www.fda.gov/animal-veterinary/animal-health-literacy/how-give-your-pet-medicine-safely) explains why dosing errors happen and how to avoid them. The [American Veterinary Medical Association's pet owner resources](https://www.avma.org/resources-tools/pet-owners) describe how to work with your veterinarian and when to seek emergency care. Use these as background, and always confirm your specific plan with the veterinarian who knows your cat's history.

## Common Mistakes Owners Make With Apoquel for Cats

**Mistake: Stopping the medication suddenly once the cat looks better.**
Apoquel controls itch quickly, often within 24 hours. That improvement can make you think the problem is gone. But the underlying allergy or skin condition is usually still active. Stopping early often brings the scratching back within a day or two. Follow the schedule your veterinarian set, and call before changing it.

**Mistake: Giving a dose meant for a dog.**
Apoquel is approved for dogs, not cats. Your veterinarian must calculate the right amount for your cat's weight and health. Never split a dog tablet by guesswork. Dosing errors can cause vomiting, lethargy, or more serious problems. The FDA's guidance on giving pet medication safely explains why exact dosing matters and why you should confirm every dose with your vet.

**Mistake: Assuming vomiting or diarrhea is always the drug.**
Apoquel can cause digestive upset, but so can hairballs, dietary changes, infections, or parasites. If your cat vomits more than once in 12 hours, has bloody stool, or seems painful, do not assume it is the medication. Call your veterinarian the same day. If your cat cannot keep water down, seek in-person care.

**Mistake: Hiding the tablet in food and not checking that it was swallowed.**
Cats are experts at eating around medication. If the tablet falls out or is spit up, you may think your cat received a dose when it did not. Watch your cat swallow. If you are unsure, do not give a second dose. Call your vet for instructions.

**Mistake: Using Apoquel for a cat with a known infection.**
Apoquel suppresses part of the immune response. If your cat has a bacterial or fungal skin infection, treating the itch without treating the infection can let it spread. Your vet may need to treat the infection first or at the same time.

| Common Mistake | Better Action |
| --- | --- |
| Stopping the drug when the cat looks better | Finish the prescribed course, then ask your vet about tapering |
| Giving a dog-sized dose | Weigh your cat and confirm the exact dose with your vet |
| Blaming every symptom on Apoquel | Track symptoms and call your vet for any new or worsening signs |
| Hiding the pill and walking away | Watch the cat swallow, then check the bowl and floor |
| Treating itch without checking for infection | Let your vet examine the skin before starting treatment |

## How to Reduce the Chance of It Happening Again

Apoquel treats the itch, not the cause. To reduce future flare-ups, work with your vet to find what triggers your cat. Common triggers include fleas, food proteins, pollen, and dust mites.

Flea control is the most important step. Even indoor cats can get fleas. Use a vet-approved flea product year-round. The American Veterinary Medical Association's pet owner resources explain how preventive care and parasite control reduce allergy flares.

If food allergy is suspected, your vet may recommend a strict food trial. This means feeding only a special diet for 8 to 12 weeks. No treats, no table scraps, no flavored medications. This is hard but often worth it.

Keep a simple log. Write down when scratching worsens, what the weather was like, what your cat ate, and any new products in the home. Bring this log to follow-up visits. Patterns become visible over weeks, not days.

## What Recovery and Ongoing Management Usually Look Like

Most cats show reduced itching within 24 to 48 hours of the first dose. Full skin healing takes longer. Raw, irritated areas need 1 to 3 weeks to grow new skin and fur. Hair loss from chronic scratching may take months to fully regrow.

Apoquel is not a cure. Many cats need it for weeks or months, and some need it long term. Your vet will likely recheck your cat after 2 to 4 weeks to assess response and run blood work if the cat will stay on the drug long term. The MSD Veterinary Manual's pet owner version describes how chronic allergy management often combines medication with environmental changes.

If Apoquel is stopped, itching usually returns within a few days. Some cats do well on a lower dose over time. Others need a different medication or a combination approach. Expect adjustments. Your vet will guide you based on your cat's response and any side effects.

## Frequently Asked Questions

**Can I give my cat Apoquel every day forever?**
Some cats do stay on Apoquel long term, but that decision belongs to your veterinarian. Long-term use requires monitoring, including periodic blood work to check liver and kidney values. Your vet will weigh the benefits against any risks for your individual cat. Do not continue refilling the prescription without a recheck. The FDA's animal drug information explains how adverse effects are tracked and why regular veterinary oversight matters for ongoing medication use.

**What if my cat misses a dose?**
Give the missed dose as soon as you remember, unless it is almost time for the next dose. In that case, skip the missed dose and continue on the normal schedule. Never give two doses at once. If you are unsure what to do, call your vet. Missing one dose is rarely dangerous, but it may cause a temporary return of itching.

**Will Apoquel make my cat sleepy?**
Some cats seem more tired or less active in the first few days. This is not the most common side effect, but it can happen. If lethargy lasts more than 48 hours, or if your cat stops eating or drinking, contact your veterinarian. Lethargy can also signal a more serious problem, so do not dismiss it.

**Can Apoquel be used with other cat medications?**
Often yes, but your vet must review the full list of medications, including flea products, supplements, and any over-the-counter items. Some combinations increase the risk of side effects. Tell your vet about everything your cat receives. Do not start a new medication without asking first.

**Is Apoquel safe for kittens?**
Apoquel is not approved for cats at all, and safety in kittens is not well established. Your veterinarian may still prescribe it off-label if the benefits are clear, but they will likely recommend extra caution and monitoring. For a kitten with severe itching, ask your vet about alternative options that have more safety data in young cats.

**How do I know if the vomiting is from Apoquel or something else?**
Watch the timing. Vomiting that starts within hours of each dose and stops when the drug is paused points to the medication. Vomiting that happens between doses, or that comes with diarrhea, fever, or appetite loss, may have another cause. If your cat vomits more than twice in 24 hours, call your vet. If there is blood in the vomit or your cat seems weak, seek emergency care immediately.

## Related Clinical & Scientific Guides

* [What Are the Side Effects of Bravecto for Dogs? What to Watch For](/knowledge/veterinary-medicine/pet-medication-guide/bravecto-side-effects-dogs)
* [Can You Give Your Dog Human Allergy Medicine? Whats Safe](/knowledge/veterinary-medicine/pet-medication-guide/dog-human-allergy-medicine-safe)
* [Can You Give Your Dog Dramamine for Car Sickness?](/knowledge/veterinary-medicine/pet-medication-guide/dog-dramamine-car-sickness)


## References and Further Reading

- [FDA Center for Veterinary Medicine Animal Drug Information](https://www.fda.gov/animal-veterinary)
- [FDA Safe Use of Pet Medications](https://www.fda.gov/animal-veterinary/animal-health-literacy/how-give-your-pet-medicine-safely)
- [AVMA Pet Owner Resources](https://www.avma.org/resources-tools/pet-owners)
- [MSD Veterinary Manual Pet Owner Version](https://www.msdvetmanual.com/pet-owners)
- [AAHA Pet Owner Resources](https://www.aaha.org/for-pet-parents/)

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> This article is general educational information for pet owners. It is not a substitute for veterinary diagnosis, examination, or treatment. If your pet is showing severe or rapidly worsening signs, contact an emergency veterinary hospital immediately.