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An insulinoma is a tumor of the insulin producing beta cells in the pancreas. It is the most common tumor of the pancreatic islet cells in dogs. A healthy pancreas releases insulin in response to food and then eases off as blood sugar falls. An insulinoma ignores that control and keeps releasing insulin even when blood sugar is already low. The extra insulin drives glucose out of the bloodstream and into body tissues, so the brain and muscles are left short of fuel. The result is hypoglycemia, or low blood sugar, which explains nearly every sign of this disease. Unlike the usually benign insulinomas of ferrets, insulinomas in dogs are considered malignant, because they tend to spread beyond the pancreas.
Owners often find the pattern confusing at first. A dog may seem completely normal for days, then have a short episode of wobbliness, confusion or collapse, then recover after eating or resting. Episodes are often triggered by exercise, excitement or a missed meal, and they become more frequent and last longer as the tumor grows. The Merck Veterinary Manual reports that in 40 to 50 percent of cases these tumors have already spread to nearby lymph nodes or the liver by the time of diagnosis. Repeated or prolonged low blood sugar can injure the brain, so episodes of weakness or seizures in a middle aged or older dog should always prompt a blood glucose check rather than watchful waiting at home. The tumors themselves are usually small. The Merck Veterinary Manual describes them as single nodules that are typically 1 to 3 cm across, which helps explain why they are rarely felt from outside and why imaging and surgery are needed to find them. Because the seizures and collapse of low blood sugar can look like primary brain disease, the Merck Veterinary Manual also notes that insulinomas may be misdiagnosed as idiopathic epilepsy or brain tumors. A simple glucose measurement during the workup of an older dog with episodic signs can redirect the whole investigation. Weight gain can also appear in some dogs, because insulin encourages the body to store energy even as blood sugar control worsens.
An insulinoma develops when beta cells in the pancreas grow into a tumor that produces insulin without normal control. Why that growth starts in a particular dog is not known, and no food, vaccine or household exposure has been shown to cause it. The tumor is usually a carcinoma arising from the insulin secreting cells, and it may appear as a single small nodule or as more than one nodule in the pancreas. Because the tumor cells behave like the cells they came from, they keep secreting insulin into the bloodstream regardless of the blood sugar level. That uncontrolled secretion, not the size of the tumor alone, is what produces the low blood sugar episodes.
Breeds and dogs at higher risk: Insulinoma is mainly a disease of middle aged and older dogs. The Merck Veterinary Manual (dog owners) reports that these tumors are most common in dogs 5 to 12 years of age, and medium to large breed dogs are represented often. Both sexes can be affected, and younger dogs are occasionally diagnosed.
Diagnosis rests on showing two things at the same time: low blood sugar and an insulin level that is inappropriately normal or high for that low sugar. A single low glucose reading can have many causes, so the veterinarian interprets paired glucose and insulin results together with the history of episodic weakness, collapse or seizures. Blood glucose should be measured in any older dog with that history. Once the paired results support an insulinoma, imaging looks for the tumor and for spread. Contrast enhanced CT is the preferred imaging method described by the Merck Veterinary Manual, while ultrasound can help assess the pancreas, liver and lymph nodes. Staging also guides whether surgery is sensible. Other causes of low blood sugar, such as liver disease, an adrenal gland disorder and other tumors, must be ruled out along the way. That is why the paired insulin result matters: it separates a tumor that overproduces insulin from other reasons blood sugar can fall.
Initial treatment focuses on safety during low blood sugar episodes, followed by a longer term plan. A dog that is collapsing or seizuring needs emergency veterinary care, where glucose can be given by vein under monitoring. Giving food to a dog that cannot swallow safely is dangerous, so home first aid is limited to keeping the dog safe and getting to a clinic quickly unless your veterinarian has given you a specific plan. For longer term control, surgery is generally the best option when the dog is a suitable candidate. Removing the tumor, often with part of the pancreas, can restore normal blood sugar and remove visible spread in lymph nodes. When surgery is not possible, or low blood sugar returns afterward, medical management takes over. Frequent small meals spread glucose intake through the day, and glucocorticoid medication helps the body maintain blood sugar. A medication that reduces insulin release, diazoxide, is described by the Merck Veterinary Manual as the preferred drug for ongoing medical control, and a tyrosine kinase inhibitor has also been reported as an option. Treatment cannot promise a cure, particularly when spread has occurred, but many dogs enjoy a good quality of life for a meaningful period with signs controlled.
Daily management aims to keep blood sugar steady and episodes rare. Feed small, regular meals on a consistent schedule rather than one or two large meals, using the diet your veterinarian recommends, and avoid long gaps without food. Keep exercise gentle and predictable, since exertion can trigger an episode, and supervise your dog outdoors until you know the pattern of any episodes. Learn your dog's early signs, such as restlessness, trembling or a glazed look, and keep a simple log of episodes, meals and medication to share at rechecks. Give prescribed medication on schedule and attend monitoring visits, because rising episode frequency often means the plan needs adjustment rather than home experiments.
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The tumor releases insulin in an uncontrolled way, but blood sugar falls lowest at certain times, such as after exercise, excitement or a missed meal. Between episodes, blood sugar may sit high enough for the dog to act normally. As the disease progresses, episodes typically become more frequent, last longer and need less of a trigger to start.
They are opposites in blood sugar terms. Diabetes involves too little effective insulin, so blood sugar runs high. An insulinoma produces too much insulin, so blood sugar falls too low. The treatments are therefore completely different, and a dog with low blood sugar episodes should never be given insulin or diabetes medication unless a veterinarian has directed it.
Surgery can remove the visible tumor and restore normal blood sugar, and it offers the best control of signs, especially for a single tumor that has not spread. Because these tumors are considered malignant in dogs and may already have spread invisibly, surgery cannot guarantee a cure. Monitoring continues after surgery even when a dog recovers well.
Keep your dog safe from falls and do not put food or liquid into the mouth of a dog that is seizuring, collapsed or unable to swallow, because of the choking risk. If your veterinarian has given you a specific home plan for early mild signs, follow it exactly. Otherwise, treat the episode as urgent and get veterinary care right away.
The outlook depends on whether the tumor has spread and how well blood sugar can be controlled. The Merck Veterinary Manual (dog owners) notes that dogs can live for more than a year with good quality of life when large tumors are removed, and medical management with diet changes and medication can also maintain quality of life for a period of time.
This page is general information drawn from the published guidance of the organizations listed under Sources below. It is not veterinary advice, and it does not replace your own veterinarian, who knows your dog. If your dog may have eaten something toxic, contact your veterinarian, the ASPCA Animal Poison Control Center on (888) 426-4435, or the Pet Poison Helpline on (855) 764-7661 straight away. A consultation fee may apply on the helplines. If your dog is struggling to breathe, has collapsed, is having a seizure that will not stop, or has a swollen belly with retching that brings nothing up, go to an emergency veterinarian now and do not wait to finish reading.
Last updated: November 2026. Facts on this page were checked against the sources listed above. How we work: our methodology.