Changes in appetite can show up in different ways, and not all of them are easy to spot. Some dogs stop eating altogether, while others continue to eat but take in much less than usual. Some may become pickier, only accepting certain foods that they previously enjoyed without hesitation.
It’s very common for these shifts to go unnoticed at first. In some cases, the change is obvious, but often, especially in busy homes or multi-dog households, a decrease in appetite can be subtle. Another dog may finish leftover food, or your pup may pick at meals just enough to make it seem like their appetite is normal.
If you only realized something was off because your dog started losing weight, please know you’re not alone. Many pet parents notice weight loss before they see the changes in eating habits. What matters most is that you’ve recognized it now, and you’re taking steps to understand what your dog needs.
Why Dogs Stop Eating
When a dog suddenly loses interest in food, the most important first step is understanding why. Unless your pup is showing signs of severe distress, taking a moment to observe their behavior can give you and your veterinarian valuable clues about what’s going on.
Two of the most common reasons dogs stop eating are digestive upset and pain. Just like us, dogs don’t want to eat when they feel nauseous or uncomfortable. And if they’re in pain—whether from their cancer or from something completely unrelated—eating can feel like an effort. It’s not that they don’t want to eat; it’s that their body isn’t allowing them to feel comfortable enough to try.
For dogs facing cancer, appetite loss can happen for many reasons:
• Cancers affecting the mouth, throat, or digestive tract can make eating physically difficult
• Chemotherapy may cause nausea or vomiting
• Tumors can release substances that naturally decrease appetite and cause weight loss
• Pain medications, especially opioids, often reduce the desire to eat
• Any type of discomfort—joint pain, muscle pain, or just “not feeling well”—can make food unappealing
Every dog expresses appetite changes differently, and it’s completely normal to feel worried when your dog isn’t eating like they used to. You’re paying attention, you’re noticing the changes, and that awareness is the first step toward helping them feel better.
Side Effects of Chemotherapy Medication
Some chemotherapy medications, like cisplatin, doxorubicin, dacarbazine, cyclophosphamide, actinomycin, and 5-FU streptozotocin, can make dogs more prone to nausea and vomiting. These side effects are very common and can understandably affect a dog’s appetite.
What many pet parents don’t realize is that these digestive changes often don’t show up right away. It can take 2–5 days after treatment for nausea to appear. So if your pup isn’t eating well a few days after a chemo session, it may be a delayed reaction to the medication rather than something new or alarming.
Knowing this timing can help you prepare, monitor your pup closely, and reach out for supportive care sooner rather than later. You're doing everything you can to help your dog through this, and you're not alone in navigating these ups and downs.
Is the End Close?
Many pet parents fear that when their dog stops eating, it’s a sign that the end is near.
It’s completely understandable to feel that way—appetite is closely tied to how we measure comfort and quality of life. But it’s important to remember that in the short term, a reduced appetite does not automatically mean your dog is dying.
Dogs can lose interest in food for many reasons, and most episodes of inappetence last only a short time. With the right support—whether that’s medication for nausea, a temporary diet change, or simple adjustments at home—many dogs begin eating again and return to their usual routines.
Where we become more concerned is when a dog refuses food for a prolonged period, doesn’t respond to treatments, or begins to lose significant weight. These situations may suggest a decline in comfort or overall quality of life. If you ever reach that point, having an open, honest conversation with your veterinarian can help you understand what your dog is experiencing and what options you have.
You’re not expected to navigate these worries alone—we’re here to help you understand what’s normal, what’s concerning, and how to support your dog every step of the way.
What You Can Do to Help Your Dog Eat
There are several gentle steps you can try at home to help encourage your dog to eat when their appetite dips. Every dog is unique, so it may take a little experimenting to find what feels best for your unique pup.
Creating a calm, quiet space for meals can make a big difference. You can also try warming their food slightly to bring out the aroma, or adding something especially enticing—like a little low-sodium bone broth or plain boiled chicken—to spark their interest.
Some dogs do well when offered a small “buffet” of options so they can choose what appeals to them in the moment. Others may feel comforted by being hand-fed. And for dogs who become nauseous around certain smells, switching from a bowl to a simple paper plate can sometimes help.
If your dog is actively vomiting, they likely won’t want to eat until the nausea settles. In that case, your focus shifts to helping them feel better first—then reintroducing food gently once they’re ready.
If Your Dog is Vomiting
If your dog is vomiting, it’s normal for them not to want to eat. In this situation, you can safely withhold food for about 12–24 hours to give their stomach time to settle. After that rest period, start by offering small sips of water.
If your dog is able to keep water down without vomiting, you can begin introducing a bland, easy-to-digest meal in very small portions. Many families use commercial gastrointestinal diets, or simple home-cooked foods like plain boiled chicken or cooked white rice.
There are also medications that can help calm nausea and gently encourage appetite.
Your veterinarian can guide you on the best plan for your dog and help determine whether supportive medication is needed. You don’t have to figure this out alone' your vet team and our community are here to support you and your pup through this.
Checking into Appetite Stimulants with Your Vet
One of the most common medications we have seen prescribed in the United States as an appetite stimulate is called Mirtazipine.
Mirtazapine helps stimulate appetite in dogs in two main ways:
It makes dogs feel hungrier, and it helps reduce nausea.
Mirtazapine increases the levels of two neurotransmitters in the brain; serotonin and norepinephrine.
These chemicals affect mood and appetite. When their levels go up, the brain sends stronger signals that say, “I’m hungry,” which helps dogs feel more interested in food.
Mirtazapine also blocks specific receptors (called 5-HT3 receptors) in the brain and the stomach that trigger nausea and vomiting.
When these receptors are blocked, the dog is less likely to feel sick to their stomach. For many dogs, especially those with kidney disease, liver problems, or going through chemotherapy, reducing nausea is a huge part of helping them eat.
Because it tackles both hunger and nausea at the same time, mirtazapine is often very helpful for dogs who aren’t eating well.
Most dogs show improvement in appetite within 24 hours of starting the medication.
Mirtazapine is used off-label in dogs, so it should always be given under the guidance of a veterinarian. There are also FDA-approved appetite stimulants for dogs, such as capromorelin (Entyce®), which your vet may recommend depending on the situation.
References
Cornell University—College of Veterinary Medicine. Managing common side-effects of chemotherapy in companion animals. https://www.vet.cornell.edu/research-departments/institutes/sprecher-institute-comparative-cancer-research/treatment-strategies/managing-common-side-effects-chemotherapy-companion-animals
Ettinger S. Take the offensive with patients fighting cancer and inappetence. DVM 360. 2019; 50(8). https://www.dvm360.com/view/take-offensive-with-patients-fighting-cancer-and-inappetence
Ettinger S. Top tips for managing chemotherapy patients in your practice. World Small Animal Veterinary Association Congress Proceedings. 2017 https://www.vin.com/apputil/content/defaultadv1.aspx?pId=20539&id=8506362
Hernandez-Avalos I, Mota-Rojas D, Mora-Medina P, et al. Review of different methods used for clinical recognition and assessment of pain in dogs and cats. Int J Vet Sci Med. 2019;7(1):43-54. Published 2019 Nov 18. doi:10.1080/23144599.2019.1680044
Theodoro SS, Tozato MEG, Ximenes TO, Volpe LM, Baptista da Silva C, Teixeira FA, Carciofi AC. Evaluation of the Short-Term Effects of Mirtazapine on Appetite Stimulants in Dogs: A Retrospective Study and a Placebo-Controlled Trial. Animals (Basel). 2025 Aug 29;15(17):2538. doi: 10.3390/ani15172538. PMID: 40941333; PMCID: PMC12427372.
Zollers B, Wofford JA, Heinen E, Huebner M, Rhodes L. A Prospective, Randomized, Masked, Placebo-Controlled Clinical Study of Capromorelin in Dogs with Reduced Appetite. J Vet Intern Med. 2016;30(6):1851-1857. doi:10.1111/jvim.14607
