Dogs get seizures when nerve cells in the brain fire abnormally, creating a sudden surge of uncontrolled electrical activity. About 1 in every 100 dogs is diagnosed with epilepsy, making it one of the most common neurological conditions in veterinary medicine. The underlying trigger can range from a genetic predisposition to toxic exposures to structural problems inside the skull.
What Happens in the Brain During a Seizure
A healthy brain maintains a careful balance between signals that excite nerve cells and signals that calm them down. The main excitatory chemical is glutamate, which tells neurons to fire. The main inhibitory chemical is GABA, which tells them to stop. A seizure occurs when this balance tips sharply toward excitation, either because there’s too much glutamate, too little GABA, or both.
When glutamate floods the spaces between neurons in high concentrations, it triggers a cascade of activity: calcium rushes into cells, enzymes activate, and if the process goes unchecked, it can even damage or kill brain cells. On the other side, anything that reduces GABA production or blocks its receptors removes the brain’s natural braking system. The result is a wave of synchronized, runaway electrical firing that produces the physical signs we recognize as a seizure.
Idiopathic Epilepsy: The Most Common Cause
The single most frequent reason dogs have seizures is idiopathic epilepsy, a condition where no underlying disease or injury can be found. It’s considered genetic in many cases and is more common in purebred dogs. Breeds with a known predisposition include Beagles, Bernese Mountain Dogs, Border Collies, Boxers, Cocker Spaniels, Labrador Retrievers, and Golden Retrievers.
Dogs with idiopathic epilepsy typically start having seizures between 6 months and 6 years of age, with a median onset around 2.5 years. A dog in this age window that has a seizure but appears completely normal between episodes is a classic presentation. Your vet will still need to rule out other causes, but age and breed are strong initial clues.
Metabolic and Organ-Related Triggers
Problems elsewhere in the body can disrupt brain chemistry enough to cause seizures, even when the brain itself is structurally healthy. Low blood sugar (hypoglycemia) and low blood calcium are two of the most recognized metabolic triggers. A condition called insulinoma, where a tumor on the pancreas drives blood sugar dangerously low, is particularly tricky because the dog often looks perfectly normal between episodes, closely mimicking idiopathic epilepsy.
Liver disease is another significant cause. Dogs with a portosystemic shunt, an abnormal blood vessel that lets blood bypass the liver, can accumulate toxins that the liver would normally filter out. Those toxins reach the brain and provoke seizures. Kidney disease and severe electrolyte imbalances can do the same. This is why bloodwork checking organ function is one of the first steps when a dog starts seizing.
Toxins and Medications
Acute poisoning is a common cause of sudden, first-time seizures in otherwise healthy dogs. Organophosphates (found in some insecticides), lead, and various household chemicals can all trigger seizure activity by disrupting the brain’s electrical signaling.
Some flea and tick medications in the isoxazoline class have also been associated with neurologic side effects, including muscle tremors and seizures. The FDA has noted that while most dogs tolerate these products without problems, seizures can occur even in animals with no prior history of neurological issues. If your dog starts having seizures shortly after beginning a new flea or tick product, that timing is worth mentioning to your vet.
Structural Brain Problems
Physical abnormalities inside the skull can directly irritate brain tissue and trigger seizures. Brain tumors are a leading structural cause, especially in older dogs. A tumor doesn’t have to be large to cause problems. It creates pressure, pushes surrounding tissue out of place, and causes swelling in nearby brain regions. That swelling alone changes the local chemical environment (shifting ion concentrations and pH) in ways that make neurons more excitable and prone to misfiring.
As a tumor grows, it can also compress blood vessels, reducing blood flow to parts of the brain. The resulting oxygen deprivation makes those areas even more seizure-prone. Beyond tumors, other structural causes include inflammation of the brain (encephalitis), infections, strokes, traumatic injuries, developmental abnormalities like hydrocephalus (excess fluid inside the skull), and degenerative diseases.
What a Seizure Looks Like in Three Phases
Most seizures follow a predictable three-stage pattern, and recognizing each phase helps you understand what your dog is experiencing.
The pre-ictal phase (sometimes called the aura) is a period of altered behavior before the seizure begins. Your dog may hide, pace, whine, shake, drool, or seek you out with unusual urgency. This phase can last anywhere from a few seconds to a few hours, and many owners learn to recognize it as a warning sign over time.
The ictal phase is the seizure itself. In a full generalized (grand mal) seizure, the dog falls on its side with violent jerking of all four limbs, paddling motions, frothing at the mouth, and possible loss of bladder or bowel control. Consciousness is lost. A generalized seizure typically lasts one to two minutes, though it can feel much longer. Not all seizures are this dramatic, though. Focal seizures affect only one area of the brain and may show up as nothing more than repetitive twitching of an eyelid, lip, or ear. Some dogs display a “fly-biting” behavior, snapping at invisible flies, or a rhythmic jaw-clacking sometimes called a “chewing gum fit.” Dogs may remain fully conscious during focal seizures.
The post-ictal phase follows immediately after the seizure stops. Your dog may appear confused, disoriented, restless, or temporarily blind. Pacing, heavy drooling, and an inability to recognize familiar surroundings are all normal during this phase, which can last minutes to hours.
Generalized vs. Focal vs. Cluster Seizures
Generalized seizures involve abnormal electrical activity across both sides of the brain simultaneously. The grand mal type (tonic-clonic) with full-body convulsions is the most recognized, but generalized seizures also come in subtler forms: tonic seizures cause stiff, rigid limbs without jerking; myoclonic seizures involve sudden limb jerks; and atonic seizures look like a dog standing, staring, and completely unresponsive.
Focal seizures are limited to one spot in the brain and tend to affect one body part or produce odd repetitive behaviors. They can sometimes progress into generalized seizures if the abnormal electrical activity spreads. Cluster seizures are defined as two or more seizures within a 24-hour period, and they carry a higher risk of complications because the brain doesn’t get enough recovery time between episodes.
How Vets Find the Cause
Because the list of possible triggers is so long, diagnosis is largely a process of elimination. Baseline bloodwork is almost always the first step, checking organ function (particularly liver and kidney), blood sugar, calcium, and electrolyte levels. If a liver shunt is suspected, bile acid testing provides more detail. A blood lead level may be checked if the dog’s environment suggests possible exposure.
If blood tests come back normal and the dog fits the typical profile for idiopathic epilepsy (young to middle-aged, purebred, normal between seizures), your vet may start treatment without advanced imaging. But if the dog shows neurological abnormalities between seizures, is outside the typical age range, or responds poorly to initial medication, brain imaging with MRI or CT is the next step. In some cases, a sample of cerebrospinal fluid is analyzed to check for infection or inflammation.
Blood tests assessing liver and kidney function also serve a practical purpose before treatment begins, since the organs responsible for processing seizure medications need to be healthy enough to handle them safely.
When Seizures Become an Emergency
A single seizure that lasts under two minutes and resolves on its own is frightening but not usually an immediate crisis. The situation becomes dangerous when a seizure continues for more than five minutes (a condition called status epilepticus) or when cluster seizures occur in rapid succession without the dog fully recovering in between. Both scenarios can cause the brain to overheat, swell, and sustain permanent damage. These situations require emergency veterinary care as quickly as possible.