# What Are the Side Effects of Seizure Medication in Cats?


## Key Takeaways

- Initial side effects of seizure medication in cats, such as drowsiness, ataxia (wobbliness), increased appetite, and thirst, are common during the first 1-3 weeks of treatment and often resolve as the cat adjusts.
- Serious adverse events requiring immediate emergency veterinary care include collapse, difficulty breathing, pale or yellow gums, and repeated vomiting, as these can indicate severe drug toxicity or a life-threatening condition.
- Phenobarbital, a common anticonvulsant, requires regular blood monitoring to ensure therapeutic drug levels and assess for potential hepatotoxicity (liver damage), which can manifest as jaundice or loss of appetite.
- Newer medications like levetiracetam (Keppra) generally have a milder side effect profile, though sedation, weakness, or gastrointestinal upset can occur and warrant veterinary consultation if persistent.
- Never abruptly discontinue seizure medication or alter the prescribed dosage without veterinary guidance, as sudden cessation can precipitate withdrawal seizures or status epilepticus, a life-threatening emergency.
- Distinguishing drug side effects from symptoms of the underlying seizure disorder or other concurrent illnesses necessitates a thorough veterinary examination, including history, physical assessment, and potentially diagnostic bloodwork to assess drug levels and organ function.

---

If your cat has been prescribed medication for seizures, you are likely watching closely for any change in behavior or health. That is a good instinct. Most cats tolerate seizure medications well, but side effects do happen, and knowing what to look for helps you act quickly when it matters.

The most common side effects in the first days to weeks are drowsiness, wobbliness, and increased appetite or thirst. These often fade as your cat adjusts. However, some side effects are serious and need immediate veterinary care. Call your emergency vet right away if your cat collapses, has trouble breathing, develops pale or yellow gums, or starts vomiting repeatedly. Do not wait to see if it passes.

Every seizure medication works differently, and every cat responds differently. Your veterinarian chose a specific drug and dose for your cat's weight, health, and seizure pattern. Never change the dose, stop the medication, or give an extra dose on your own. The dose must come from your treating veterinarian, because the right amount depends on your cat's blood levels, kidney and liver function, and how well the seizures are controlled.

## Is This an Emergency?

Use this table to decide how quickly to act. When in doubt, call your veterinarian. They know your cat's history and can guide you.


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 "title": "Urgency triage by severity of signs",
 "tiers": [
  {
   "tier": "danger",
   "label": "Go to an emergency vet now",
   "signs": [
    "Collapse or fainting, difficulty breathing or open-mouth breathing, gums that look pale, white, blue, or yellow, repeated vomiting, a seizure that lasts longer than 5 minutes, two or more seizures within 24 hours, your cat cannot stand or walk at all"
   ],
   "action": [
    "Stop what you are doing and transport your cat to the nearest open emergency clinic",
    "Call ahead if you can, but do not delay"
   ]
  },
  {
   "tier": "warn",
   "label": "Book a same-day appointment",
   "signs": [
    "New or worsening wobbliness that prevents normal walking, extreme lethargy where your cat will not get up to eat or use the litter box, refusal to eat for more than 24 hours, vomiting once or twice, diarrhea lasting more than a day, unusual aggression or hiding that is out of character"
   ],
   "action": [
    "Call your regular veterinary clinic when they open and explain the signs",
    "They will tell you if you should come in today or go to urgent care"
   ]
  },
  {
   "tier": "safe",
   "label": "Watch at home for 48 hours",
   "signs": [
    "Mild sleepiness in the first week, slight unsteadiness that improves each day, increased thirst and urination, increased appetite, mild weight gain, soft stools that firm up within a day or two"
   ],
   "action": [
    "Keep giving medication exactly as prescribed",
    "Monitor your cat's eating, drinking, and litter box use twice a day",
    "If signs get worse or do not improve after 48 hours, call your vet"
   ]
  }
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| Urgency Level | Signs You Can See | What to Do |
|---|---|---|
| Go to an emergency vet now | Collapse or fainting, difficulty breathing or open-mouth breathing, gums that look pale, white, blue, or yellow, repeated vomiting, a seizure that lasts longer than 5 minutes, two or more seizures within 24 hours, your cat cannot stand or walk at all | Stop what you are doing and transport your cat to the nearest open emergency clinic. Call ahead if you can, but do not delay. |
| Book a same-day appointment | New or worsening wobbliness that prevents normal walking, extreme lethargy where your cat will not get up to eat or use the litter box, refusal to eat for more than 24 hours, vomiting once or twice, diarrhea lasting more than a day, unusual aggression or hiding that is out of character | Call your regular veterinary clinic when they open and explain the signs. They will tell you if you should come in today or go to urgent care. |
| Watch at home for 48 hours | Mild sleepiness in the first week, slight unsteadiness that improves each day, increased thirst and urination, increased appetite, mild weight gain, soft stools that firm up within a day or two | Keep giving medication exactly as prescribed. Monitor your cat's eating, drinking, and litter box use twice a day. If signs get worse or do not improve after 48 hours, call your vet. |

## What Is Most Likely Happening: Adjustment Side Effects

When your cat starts a seizure medication, the brain and body need time to adapt. Drugs like phenobarbital, a common antiseizure medicine, act on the central nervous system to calm abnormal electrical activity. During the first one to three weeks, many cats show sedation, meaning they sleep more and seem less alert. They may also have ataxia, which is a medical word for a wobbly, uncoordinated walk. These effects are usually mild and improve as the body adjusts.

Increased thirst and appetite are also common, especially with phenobarbital. You may notice your cat drinking more water, urinating more often, and begging for food. This is not a sign of failure. It is a known effect of the drug. Keep fresh water available and follow your vet's advice on feeding. If your cat gains weight steadily, mention it at the next checkup.

## What Else Could Be Going On: Blood Level and Organ Effects

Some side effects appear because the medication level in the blood is too high. Your veterinarian may recommend blood tests to measure the drug concentration. This is routine and important. A level that is too high can cause severe sedation, weakness, and loss of coordination that does not improve. A level that is too low may not control seizures. Only a blood test can tell the difference, which is why dosing must come from your veterinarian and not from guesswork.

Phenobarbital is processed by the liver. In rare cases, it can cause liver damage over months or years. Signs include yellowing of the gums or skin, called jaundice, vomiting, loss of appetite, and extreme tiredness. The US Food and Drug Administration provides guidance on safe use of pet medications, including the importance of following label instructions and reporting unusual reactions to your veterinarian. Regular blood work helps catch liver changes early, before they become serious.

## What Else Could Be Going On: Drug-Specific Reactions

Newer medications such as levetiracetam, often sold under the brand name Keppra, tend to cause fewer side effects than phenobarbital. When they do occur, they are usually mild drowsiness or weakness in the first few days. Some cats develop diarrhea or a reduced appetite. These signs often resolve on their own, but persistent vomiting or refusal to eat warrants a call to your vet.

A rare but serious reaction to any medication is an allergic response. Watch for swelling of the face, lips, or eyelids, hives, which are raised bumps on the skin, or sudden difficulty breathing. These signs can appear within minutes to hours after a dose. They are emergencies. Do not try to treat this at home. Seek in-person emergency care immediately.

## What Else Could Be Going On: The Underlying Condition

Sometimes the signs you worry about are not from the medication at all. They may come from the seizure disorder itself or from another illness. For example, a cat with epilepsy may have post-ictal behavior, meaning confusion, pacing, or temporary blindness after a seizure. This can look like a drug side effect but is actually part of the seizure event.

Other conditions, such as kidney disease, thyroid problems, or infections, can cause lethargy, vomiting, or changes in appetite. These cannot be distinguished from drug side effects without a veterinary examination and testing. The American Veterinary Medical Association advises pet owners to work closely with their veterinarian to monitor treatment and report any new signs. Do not assume a new symptom is harmless. A quick call to your clinic can save you worry and catch a problem early.

Your role is to observe and report. Keep a simple log of your cat's appetite, water intake, energy level, and any seizure activity. Bring that log to every veterinary visit. This information helps your vet adjust treatment safely and gives you confidence that you are doing the right thing for your cat.

## What You Can Safely Do at Home Right Now

If your cat is already on seizure medication and you are seeing side effects, your first job is to keep them safe and comfortable while you gather information. Do not stop the medication. Suddenly stopping an anti-seizure drug can trigger withdrawal seizures, and in some cases those can be worse than the original problem. If you are worried the drug is causing harm, call your veterinarian before making any changes.

Keep your cat in a quiet, familiar space. Reduce noise and bright light. Make sure fresh water is always available, because some seizure drugs increase thirst. If your cat is wobbly or drowsy, keep them away from stairs, high furniture, and other pets. A soft bed on the floor is a good choice during the adjustment period.

Do not give any over-the-counter remedies, human medications, or supplements without explicit approval from your veterinarian. Many common human pain relievers are toxic to cats. Even something as simple as an antacid can change how a seizure drug is absorbed. 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 and extra medications are among the most common problems seen in pets.

## What to Write Down Before You Call the Vet

Your veterinarian will make better decisions with specific observations. Keep a notebook or a note on your phone and record the following:

- The date and time of each dose you gave.
- The exact amount you gave, and whether your cat kept it down.
- How many times your cat vomited or had diarrhea in the past 24 hours.
- Whether your cat is eating and drinking, and roughly how much.
- How many times your cat has had a seizure, and how long each one lasted.
- Any new behaviors: pacing, staring, hiding, excessive drooling, or unusual vocalizing.
- Whether your cat seems more sleepy than usual, and whether they can still walk normally.
- Any changes in gum color. Healthy cat gums are pink. Pale, white, blue, or yellow gums are a reason to seek emergency care.
- Your cat's breathing rate at rest. Count breaths for 30 seconds while they are sleeping or lying still, then multiply by two. Normal is usually 20 to 30 breaths per minute. Faster than 40 at rest is a concern.

Take a short video of any unusual movement or behavior. A video is often more useful than a verbal description, because subtle twitching or tremors can be hard to describe accurately.

## Side-Effect Comparison Table for Common Seizure Meds

This table summarizes the more common side effects reported for the three most frequently prescribed seizure medications in cats. It is not a complete list, and every cat responds differently. Your veterinarian will choose a drug based on your cat's specific condition, and dosing must come from the treating veterinarian. Never adjust a dose on your own.

| Medication | Common Side Effects | Signs to Watch For | Notes |
|---|---|---|---|
| Phenobarbital | Increased thirst and urination, increased appetite, sedation, wobbliness | Drinking more, larger urine clumps, weight gain, sleeping more in the first weeks | Sedation often improves after 2 to 3 weeks. Long-term use requires periodic blood tests. |
| Levetiracetam (Keppra) | Sleepiness, weakness, reduced appetite, vomiting | Lying around more, eating less, occasional vomiting | Often better tolerated than phenobarbital. Side effects may be milder and shorter-lived. |
| Potassium bromide | Sedation, increased thirst and urination, vomiting, unsteady gait | Drinking more, vomiting, stumbling, especially in the first month | Less commonly used in cats than in dogs. Can irritate the stomach. |

## What a Veterinary Visit Usually Involves

When you bring your cat in for a side-effect concern, the veterinarian will start with a full history. Expect questions about when the medication was started, what dose you are giving, how your cat is behaving at home, and whether there have been any seizures since starting treatment. Bring your notes and any video you recorded.

The physical examination will include checking your cat's weight, gum color, heart rate, breathing, and abdominal feel. The veterinarian will also assess your cat's balance and mental state. These checks help distinguish a mild adjustment reaction from a more serious problem.

Bloodwork is common for cats on seizure medication, especially phenobarbital. A blood test measures the drug level in the bloodstream to confirm it is in the therapeutic range, and it checks liver and kidney function. These organs process and clear the medication, so they need monitoring. The [MSD Veterinary Manual for pet owners](https://www.msdvetmanual.com/pet-owners) describes why routine monitoring is part of safe long-term seizure care. Depending on the drug and your cat's health, bloodwork may be repeated at intervals over the first year and then annually.

Costs vary widely by region and clinic. A basic office visit typically runs from 50 to 150 dollars. Bloodwork panels add roughly 100 to 300 dollars depending on what is included. Drug level testing can add another 50 to 150 dollars. These are general ranges only, not quotes. Your clinic can give you an estimate before testing.

## 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 a seizure lasting more than a few minutes, has multiple seizures in a row, is struggling to breathe, has pale or blue gums, collapses, or cannot stand, that is an emergency. Seek in-person emergency care immediately. A remote consultation cannot stabilize a seizing cat, give injectable medication, or run the tests needed to rule out a life-threatening cause. The [AVMA's pet owner resources](https://www.avma.org/resources-tools/pet-owners) list the signs that require immediate veterinary attention.

A remote consultation is genuinely useful in other situations. If your cat started a new medication and seems sleepier than usual, or vomited once and otherwise seems fine, a video call can help you decide whether a visit is needed. If your cat has been stable for months and you have a question about a mild change in appetite or energy, remote advice can be practical. If you are unsure whether a behavior is a side effect or a seizure, showing a video to a veterinarian can clarify the next step.

A remote veterinarian can take a detailed history, watch visible signs on video, advise on monitoring, and in many states prescribe medication. But they cannot palpate the abdomen, listen to the chest, take a temperature, run bloodwork, or image anything. Those limitations matter. Prescribing rules differ by state, and a veterinarian may require an in-person examination before starting or changing a prescription. Use remote care as a triage tool and a follow-up option, not as a replacement for hands-on diagnosis when your cat is unwell.

## Common Mistakes Owners Make With Seizure Medication

Managing a cat on seizure medication involves more than giving a pill twice a day. Owners often stumble in predictable ways, and knowing these pitfalls can save you and your cat a great deal of stress.

**Mistake: Stopping the medication abruptly when the cat seems better.** Seizure medications control seizures, they do not cure the underlying condition. Stopping suddenly can trigger a severe cluster of seizures or a prolonged seizure called status epilepticus, which is life-threatening. Always taper off under veterinary supervision, even if your cat has been seizure-free for months.

**Mistake: Doubling a dose after a missed one.** If you forget a dose, give it as soon as you remember, unless the next dose is due within a few hours. In that case, skip the missed dose and resume the normal schedule. Never give two doses at once. Doubling can cause dangerous sedation, wobbliness, or worse. The [FDA's guidance on giving pet medication safely](https://www.fda.gov/animal-veterinary/animal-health-literacy/how-give-your-pet-medicine-safely) stresses that dosing errors are one of the most common problems in home treatment.

**Mistake: Assuming a generic brand is identical.** Generic versions of phenobarbital or levetiracetam (Keppra) are usually fine, but they are not always bioequivalent in every cat. If your pharmacy switches brands and your cat's seizure control changes, tell your vet. Consistency matters more than brand loyalty.

**Mistake: Hiding pills in food without checking that the cat ate the whole dose.** Cats are experts at eating around pills. If you use a pill pocket or wet food, watch your cat swallow. A half-eaten dose can mean a half-controlled seizure.

**Mistake: Ignoring mild side effects for too long.** Sedation in the first week is normal. Sedation that persists for a month is not. Waiting "to see if it passes" can delay a needed dose adjustment or a switch to a different drug.

| Common Mistake | Better Action |
| --- | --- |
| Stopping meds when seizures stop | Continue as prescribed, taper only with vet approval |
| Doubling up after a missed dose | Skip if close to next dose, never give two at once |
| Assuming brand changes are harmless | Tell your vet about any pharmacy switch |
| Not verifying the pill was swallowed | Watch your cat swallow, check the mouth after |
| Waiting weeks to report persistent side effects | Call your vet after 7 to 10 days of ongoing issues |

## How to Reduce the Chance of It Happening Again

Seizure recurrence is not fully preventable, but you can lower the odds. Give medication at the same times every day, roughly 12 hours apart for twice-daily drugs. Use a pill organizer or set a phone alarm. Keep a written log of every dose, every seizure, and any unusual behavior.

Regular blood tests are not optional for phenobarbital. This drug has a narrow safety window, meaning the difference between a helpful level and a toxic level is small. Your vet will check blood levels after starting the drug, again after a few weeks, and then every 6 to 12 months. These tests also monitor liver function, since phenobarbital is processed by the liver. The [American Veterinary Medical Association's pet owner resources](https://www.avma.org/resources-tools/pet-owners) emphasize that routine monitoring is part of responsible long-term care for chronic conditions.

For levetiracetam (Keppra), blood level monitoring is less critical because the drug has a wider safety margin. Still, your vet may check kidney function, especially in older cats, since the drug is cleared through the kidneys.

Reduce seizure triggers where you can. Stress, missed doses, and changes in sleep patterns can lower the seizure threshold. Keep routines predictable. If you travel, bring enough medication and a written record of the dosing schedule.

## What Recovery and Ongoing Management Usually Look Like

Most cats adjust to seizure medication within 1 to 3 weeks. The first few days often bring noticeable sleepiness, a wobbly gait, or increased appetite. These effects usually fade as the brain adapts. If they do not fade, the dose may need adjustment.

Seizure control is not all or nothing. A good outcome means fewer seizures, shorter seizures, or less intense seizures. Many cats still have an occasional breakthrough seizure even on medication. That does not mean the drug failed. It means the dose or drug choice may need review.

Ongoing management is a partnership. Expect a veterinary check every 3 to 6 months, with blood work at least yearly. Your vet will ask about seizure frequency, side effects, and quality of life. Be honest about what you see. A cat that is sedated all day is not well managed, even if seizures have stopped.

Long-term prognosis depends on the underlying cause. Cats with idiopathic epilepsy, meaning no structural brain cause is found, often do well for years. Cats with brain tumors or other structural disease may need additional treatment. The [MSD Veterinary Manual's pet owner version](https://www.msdvetmanual.com/pet-owners) explains that epilepsy in cats is often manageable but rarely cured, and treatment is typically lifelong.

## Frequently Asked Questions

**Can I give my cat human seizure medication?**
No. Human formulations may contain different inactive ingredients, and the dose is almost never the same as the veterinary prescription. Giving human medication without veterinary direction risks overdose or underdose. Always use the medication your veterinarian prescribed, and ask your pharmacy to confirm the strength and formulation before you leave the counter.

**My cat is sleeping more than usual. Is this normal?**
In the first 1 to 2 weeks, yes. Phenobarbital and levetiracetam both cause sedation initially. Your cat may sleep more, seem less playful, or walk with a slight wobble. These effects usually improve. If your cat is difficult to wake, is not eating, or the sleepiness lasts beyond 3 weeks, call your vet. That pattern can indicate a dose that is too high or a drug level that needs checking.

**What if my cat has a seizure while on medication?**
Stay calm. Move the cat away from stairs or sharp objects, do not put your hand near the mouth, and time the seizure. Most seizures last under 2 minutes. If it lasts longer than 5 minutes, or if seizures repeat without full recovery in between, this is an emergency. Seek in-person emergency care immediately. After any seizure, call your regular vet to report it, even if the cat recovers quickly.

**How long will my cat need this medication?**
For most cats, lifelong. Seizure disorders are chronic conditions, and stopping medication usually allows seizures to return. Some cats with a single, isolated seizure may not need long-term treatment, but cats with recurrent seizures typically stay on medication for life. Your vet will reassess periodically, but plan for ongoing treatment.

**Will the medication change my cat's personality?**
Some cats become more affectionate or more subdued in the first weeks. True personality changes are uncommon but possible. If your cat becomes aggressive, hides constantly, or seems depressed beyond the adjustment period, report it. A dose change or a different drug may restore your cat's usual temperament.

**What should I do if I cannot afford the medication or blood tests?**
Tell your vet. Do not skip doses or stretch out blood work on your own. Some clinics offer payment plans, and generic versions of phenobarbital and levetiracetam are often affordable. Your vet can also discuss which monitoring tests are essential versus optional. Cost should never be a reason to stop treatment abruptly, as that can trigger a life-threatening seizure cluster.

## 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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- [What Are the Side Effects of Gabapentin for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-cats)
- [What Are the Side Effects of Seizure Medication in Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/seizure-medication-side-effects-dogs)
- [What to Expect When Your Dog Starts Seizure Medication: Side Effects and Adjustments](/knowledge/veterinary-medicine/pet-medication-guide/dog-seizure-medication-side-effects)
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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.