Why Is My Dog With Cancer Shaking or Trembling?

The most common reason a dog with cancer shakes or trembles is pain. Not cold, not anxiety, and not simply old age, though all three are real and all three get blamed far more often than they should be.

Trembling is one of the ways dogs show discomfort, and pain in dogs with cancer is frequently under-recognized because dogs are poor at advertising it. Current pain guidelines emphasize that assessing pain in dogs requires observing posture, gait, and behavior rather than waiting for obvious distress, and that what an owner notices at home is a central part of that assessment (Gruen et al., 2022).

But pain is not the only explanation, and a few of the alternatives are emergencies. Trembling can be the outward sign of a fever during chemotherapy, dangerously low blood sugar, high blood calcium, or internal blood loss. Each of those needs same-day attention, and two of them need it within hours.

So the honest answer is that trembling is a symptom worth taking seriously rather than watching. If your dog is shaking today and something else also seems wrong, this is a phone call, not a wait-and-see.

Key points

• Pain is the most likely cause, and it is treatable. Trembling that comes with reluctance to move, a hunched posture, panting, or restlessness at night points strongly this way.
• Fever plus trembling in a dog receiving chemotherapy is an emergency. Febrile neutropenia is classified as an oncologic emergency requiring hospitalization (Christensen et al., 2026).
• Low blood sugar causes trembling, weakness, disorientation, and seizures. It is most associated with insulinoma, a pancreatic tumor, and episodes are often triggered by exercise or a missed meal.
• High blood calcium is one of the most common paraneoplastic syndromes in dogs, most often linked to lymphoma and anal sac tumors, and tremors are among the reported signs (Merck Veterinary Manual, 2024).
• Nausea makes dogs shiver, and it is common in the days after chemotherapy. It responds well to medication.
• Sudden trembling with pale gums, weakness, or a swollen abdomen can mean internal bleeding from a tumor. This is an emergency.
• Trembling and a focal seizure can look similar. Whether your dog is responsive to you during the episode is the most useful thing you can note.

Detailed explanation

First, work out what you are actually seeing

Before anything else, try to establish whether this is trembling or something neurological.

Trembling or shivering is usually a fine, continuous shake affecting the body or limbs. Your dog stays aware of you throughout. They will look at you if you speak, follow you with their eyes, and respond to their name. They can usually still walk, even if reluctantly.

A focal seizure can look deceptively similar. The giveaway is responsiveness. During a seizure, a dog is typically not fully aware of you, may stare fixedly, may chew or paddle, may drool or lose bladder control, and often seems dazed or disoriented afterward. Episodes tend to have a clear start and end rather than continuing steadily.

If you can film it, do. A twenty-second phone video is worth more than any description, and your veterinarian will thank you for it.

Also note the pattern. Constant trembling suggests something ongoing like pain or metabolic disturbance. Episodic trembling that comes and goes, especially around exercise or meals, points toward blood sugar.

Pain: the most common explanation and the most missed

Dogs evolved to hide pain, and they are good at it. A dog trembling in the kitchen at eleven at night is not being dramatic. They are usually telling you something they have been trying not to tell you all day.

The 2022 pain guidelines make the point that recognizing pain is fundamental to treating it, that observation of posture, gait, and behavior must be part of the assessment, and that owner-reported behavioral change carries real diagnostic weight (Gruen et al., 2022). Your observations are data, not anecdote.

Signs that tend to travel with pain-related trembling include a hunched or tucked posture, reluctance to lie down or difficulty settling, panting without heat or exertion, pacing or restlessness that is worse in the evening, reluctance on stairs or jumping, licking repeatedly at one area, changes in facial expression, and a dog who becomes withdrawn or unusually clingy.

Cancer pain has several sources. Bone tumors are among the most painful conditions in veterinary medicine. Tumors pressing on nerves, stretching an organ capsule, or obstructing something hollow all hurt. Surgical sites hurt during recovery. And many older dogs with cancer also have osteoarthritis that was quietly manageable until something else tipped the balance.

The practical point is that this is fixable. Pain in dogs with cancer can almost always be improved, and if your dog is trembling and already on pain medication, that means the current plan needs adjusting rather than that nothing more can be done. Increasing discomfort does not automatically mean giving more of the same drug. It usually means a conversation about a different or additional approach.

Nausea

Nauseated dogs shiver. They also lip-smack, drool, swallow repeatedly, turn away from food, and sometimes eat grass. Owners often read the shivering as cold and miss the rest of the picture.

This is common in the days following chemotherapy. Gastrointestinal upset from conventional protocols typically lasts around three days and usually responds to supportive medication (Christensen et al., 2026). Nausea is also a driver of the appetite loss that leads many owners to stop treatment early, which is precisely why guidelines urge reporting even mild changes in eating promptly rather than waiting.

If your dog is within a week of chemotherapy and is trembling and off food, call. This is one of the most fixable items on this list.

Fever, and why it matters more during chemotherapy

Shivering is how a body raises its temperature. A trembling dog may be running a fever.

In a dog receiving chemotherapy, this is urgent rather than routine. Bone marrow suppression is the main dose-limiting effect of conventional chemotherapy, with the lowest white cell counts typically falling around a week after treatment, and fever combined with low neutrophils is classified as an oncologic emergency requiring hospitalization (Christensen et al., 2026).

The difficult part is that a dog can look reasonably well and still be in this situation. If you have a thermometer and know how to use it, take a temperature. If you do not, do not delay the call trying to obtain one. Trembling plus lethargy in the week after chemotherapy warrants a phone call regardless of what the thermometer says.

Low blood sugar

Hypoglycemia produces trembling through two routes: the brain running short of glucose, and the surge of stress hormones the body releases in response.

In dogs with cancer this is most associated with insulinoma, an insulin-secreting pancreatic tumor. Reported signs include weakness, collapse, disorientation, seizures, and trembling or muscle twitching, and episodes are characteristically intermittent, often triggered by exercise, by fasting, or sometimes by eating (Ryan et al., 2021). Large liver tumors and severe illness can also drop blood sugar.

The pattern to watch for is episodes rather than constancy. A dog who trembles and seems vague after a walk, then appears normal twenty minutes later, then does it again days afterward, is describing a metabolic problem rather than a behavioral one.

If your dog is known or suspected to have an insulinoma, your veterinarian should already have given you a specific plan for what to do during an episode. Follow that plan. If you do not have one, ask for it at the next appointment, because these episodes tend to happen outside business hours.

High blood calcium

Hypercalcemia is one of the more common paraneoplastic syndromes in dogs, meaning a problem the tumor causes at a distance rather than by direct invasion. It is most often linked to lymphoma and to apocrine gland anal sac adenocarcinoma, though many other cancers can produce it. Reported signs include increased thirst and urination, weakness, lethargy, reduced appetite, weight loss, vomiting, and tremors (Merck Veterinary Manual, 2024).

The combination worth flagging to your veterinarian is trembling alongside a noticeable increase in drinking and urinating. That pairing is worth a blood calcium check, and it is a simple test. Untreated high calcium damages the kidneys, so this is a same-week concern rather than something to raise at the next routine visit.

Blood loss and sudden weakness

Some tumors bleed. Splenic and liver masses, hemangiosarcoma in particular, can rupture and bleed into the abdomen, sometimes without warning.

The picture here is different from the others. Trembling comes on suddenly and is accompanied by profound weakness, pale or white gums, rapid breathing, a distended abdomen, and sometimes collapse. Some dogs appear to recover partially before deteriorating again.

This is an emergency in the true sense. Go now, do not wait for morning, and call ahead so the practice is ready.

Medications

Several drugs used in dogs with cancer can cause trembling, restlessness, or muscle twitching. Steroids commonly cause panting, restlessness, and difficulty settling. Some anti-nausea medications can produce restlessness or unusual movement in a minority of dogs. Opioid pain medications sometimes cause trembling or disorientation, particularly at the start of treatment or after a change.

Timing is the clue. If the trembling started within a few days of a new medication or a change to an existing one, mention that specifically when you call. Do not stop a prescribed medication on your own, but do report the connection, because adjusting the drug is often straightforward.

Neurological causes

Brain tumors, whether primary or spread from elsewhere, can cause tremors, altered behavior, circling, head pressing, or seizures. Cancer affecting the spinal cord or nerves can produce weakness and shaking in specific limbs rather than the whole body.

If trembling is accompanied by changes in personality, disorientation, walking into things, circling in one direction, head tilt, or difficulty with one side of the body, say so directly when you call. That combination changes the urgency and the workup.

Cold, anxiety, and old age

These are genuine causes. Small breeds, thin dogs, and dogs who have lost muscle or body fat to illness genuinely get cold more easily. Anxious dogs tremble, and a dog who has been to the clinic repeatedly may have developed real anxiety about it. Some older dogs develop benign tremors, often most visible in the hind legs when standing.

The reason these sit at the end of this article rather than the beginning is that they are conclusions to reach after ruling things out, not assumptions to start with. A dog with cancer who begins trembling deserves the other explanations considered first.

That said, if your dog is trembling only in specific circumstances, is otherwise bright, eating well, and moving normally, and the trembling stops when they are warm and settled, the benign explanations become much more plausible. Mention it at your next appointment rather than treating it as an emergency.

What to note before you call

You will get better help faster with a few specifics ready:

When it started, and whether it is constant or episodic. Whether your dog is responsive to you during episodes. What else has changed: appetite, drinking, urination, energy, breathing, toileting. Gum color, if you know how to check. Body temperature, if you have a thermometer. When the last chemotherapy treatment was, if applicable. Every medication and supplement your dog is receiving, including anything you have added yourself. And a video if you can get one.

A simple daily record of appetite, energy, and anything unusual makes this far easier, and it turns "he has been a bit off lately" into something a clinician can actually work with.

When to contact a veterinarian

Go to an emergency service now if your dog is trembling and also has:

• Pale, white, or grey gums
• Collapse, or weakness so severe they cannot stand
• Labored or rapid breathing
• A swollen, distended, or painful abdomen
• A seizure, or repeated episodes of unresponsiveness
• Disorientation, unresponsiveness, or inability to recognize you

Call your veterinary practice the same day if your dog is trembling and also has:

• A fever, or trembling and lethargy within about a week of chemotherapy
• Stopped eating, or is refusing food they would normally take
• A noticeable increase in drinking and urinating
• Repeated vomiting or diarrhea
• Obvious signs of pain, such as a hunched posture, reluctance to move, or difficulty settling
• Trembling that started after a new medication or a dose change

Raise it at the next appointment if:

• Trembling is occasional, mild, happens only when your dog is cold or anxious, and your dog is otherwise bright, eating normally, and moving comfortably.

If you are unsure which category you are in, call. Veterinary teams would far rather answer a phone call that turns out to be nothing than see a dog twelve hours later than they should have.

Questions to ask your veterinarian

• Do you think this is pain? If so, can we adjust the plan rather than just continuing what we are doing?
• Should we check bloodwork, and would that include calcium and blood glucose?
• Is my dog's cancer type one that causes high calcium or low blood sugar?
• Could any of my dog's current medications be causing this?
• Was that trembling episode a seizure? Here is a video.
• What signs would mean I should go to emergency rather than wait for you?
• If this is pain, what should I expect the medication to change, and by when?
• Do we have a written plan for what I do at home if this happens again out of hours?

Sources

Christensen, J., Johnson, K., Ettinger, S., Garrett, L., Gordon, I., Ireifej, S., Love, A., & Wisecup, M. (2026). AAHA oncology guidelines for dogs and cats. Journal of the American Animal Hospital Association, 62(1), 1–37. https://doi.org/10.5326/JAAHA-MS-7549

Gruen, M. E., Lascelles, B. D. X., Colleran, E., Gottlieb, A., Johnson, J., Lotsikas, P., Marcellin-Little, D., & Wright, B. (2022). 2022 AAHA pain management guidelines for dogs and cats. Journal of the American Animal Hospital Association, 58(2), 55–76. https://doi.org/10.5326/JAAHA-MS-7292

Merck Veterinary Manual. (2024). Hypercalcemia in dogs and cats. https://www.merckvetmanual.com/endocrine-system/the-parathyroid-glands-and-disorders-of-calcium-regulation-in-dogs-and-cats/hypercalcemia-in-dogs-and-cats

Ryan, D., Pérez-Accino, J., Gonçalves, R., Czopowicz, M., Bertolani, C., Tabar, M. D., Puig, J., Ros, C., & Suñol, A. (2021). Clinical findings, neurological manifestations and survival of dogs with insulinoma: 116 cases (2009-2020). Journal of Small Animal Practice, 62(7), 531–539. https://doi.org/10.1111/jsap.13318

This article is for educational purposes only and is not a substitute for veterinary care. It describes possible causes in general terms and deliberately does not include drug doses. Never start, stop, or change a prescribed medication without speaking to your veterinarian. If your dog is trembling alongside pale gums, collapse, labored breathing, a swollen abdomen, or a seizure, seek emergency veterinary care immediately.