Why Is My Cat Losing Weight? Common Causes and What To Do

If your cat is losing weight and you don’t know why, it may be a sign of an underlying health issue and should be evaluated by a veterinarian.  

While weight loss can sometimes happen because a cat isn’t eating enough, it can also be linked to conditions such as dental disease, intestinal parasites, diabetes, hyperthyroidism, kidney disease, or other medical concerns. 

Because a cat’s fur can hide gradual changes in body condition, weight loss is often noticed later than pet parents expect. Any unexplained weight loss—especially in senior cats—warrants a veterinary visit to identify the cause and start appropriate treatment if needed. 

Reasons Your Cat Might Be Losing Weight

Here are a few common reasons why your cat is losing weight. 

1. They’re Not Getting Enough Food 

Sometimes, your cat is eating less than you think. Ask yourself some questions: 

• Do you have another cat or dog in the house? Additional pets in your home could be eating your cat’s food or obstructing your cat’s access to their food bowl. 

• Did you recently change your cat's food? The calorie content in a cup of food can vary greatly from one brand to another. 

• Is the food dish easy to access? Your cat could be experiencing pain, such as from arthritis, that’s making it difficult to jump up to a food dish kept on the counter or to go up and down stairs if it’s on a different floor. 

Your veterinarian can help you determine if there are obstacles in your home that are preventing your cat from eating enough food. 

2. Intestinal Parasites 

Intestinal parasites are common in cats and can lead to a cat losing weight if left untreated. 

Pregnant mothers can give their kittens parasites, and they can also pass parasites through their milk when they are nursing. Cats can also get parasites from hunting and eating prey, or even by walking through contaminated grass and dirt and then grooming. 

Your vet can examine your cat’s feces to determine if they’re carrying parasites that might be causing weight loss.  

If parasites are the cause, a simple dewormer can put your cat back on the road to a healthy weight. 

3. Feline Diabetes 

Diabetes in cats is very common and requires immediate veterinary care and ongoing treatment.  

In addition to unexplained weight loss, diabetic cats typically drink an abnormally large amount of water and urinate large volumes as well. 

Without treatment, diabetes can be a life-threatening condition.  

If your vet suspects diabetes, they will likely take blood and urine samples to confirm the diagnosis. Successful treatment involves diet changes and insulin.  

Any noticeable weight loss in your cat warrants a visit to your veterinarian to rule out serious health conditions. 

4. Feline Hyperthyroidism 

Middle-aged and senior cats can be at risk for hyperthyroidism, which can cause weight loss in cats. 

The thyroid is a butterfly-shaped organ in the throat. It produces hormones that perform many functions, including regulating the body’s metabolism. 

In a hyperthyroid cat, their metabolism goes into overdrive—they lose weight, are ravenously hungry all the time, have a very high heart rate, and often meow at night and have trouble sleeping. They may also drink a lot of water and urinate large amounts. 

Your vet will do blood work to see if this is the cause of the weight loss. Treatment of hyperthyroidism involves controlling the thyroid gland, either with medicine like methimazole, special food, or inpatient radioactive iodine treatment. 

 Your vet will guide you in choosing the best treatment. 

5. Feline Viral Disease 

FIP, FeLV and FIV are viral diseases in cats. These viruses have different causes and possible therapies, but weight loss is a common symptom of all three. 

If your vet suspects a virus is the cause of your cat’s weight loss, they may perform tests to determine if one of these viruses is the cause. If a diagnosis is made, management and treatment will be based on the symptoms your cat is showing. 

6. Feline Kidney Disease 

Feline kidney disease can also lead to weight loss in your cat. To determine if kidney disease is the cause of your cat’s weight loss, your vet will do blood work and a urinalysis. Treatment may include prescription food, medicine, and even sterile fluids that your vet can teach you to administer at home. 

7. Feline Cancer 

Many forms of cancer can cause weight loss. 

The diagnosis and treatment plan will vary depending on the cancer’s type and stage. Your vet might do some the following to confirm a diagnosis: 

• Blood work 

• Urinalysis 

• X-rays 

• Ultrasounds 

• Fine needle aspirations (FNA) or biopsies 

Why Is My Older Cat Losing Weight?

Older cats can lose some weight as a normal part of aging as they lose muscle mass. However, as they age, cats may also develop certain medical conditions such as diabetes, kidney disease, hyperthyroidism, and cancer, which can also lead to weight loss.  

For senior pets, it’s best to be proactive about their care and to screen them for weight loss as well as illness. Often this means vet visits and blood work every six months to assess their blood sugar, thyroid, and kidneys. 

If your pet develops acute signs such as vomiting, diarrhea, anorexia, or dramatic weight loss, it’s best to see the vet right away. 

When To See Your Vet

Unintentional weight loss in cats is a nonspecific sign that can have many causes. An examination and blood work are usually needed to determine the underlying cause. 

If you notice that your cat is losing weight, call their vet immediately to make an appointment.   

Your vet should have a documented weight from the last visit and can confirm the weight loss. 

They will take a thorough history and do a complete physical exam.  

Based on those findings, your vet might recommend a fecal exam to check for intestinal parasites and blood work to check for clues to determine what is causing the weight loss. 

Treating a Cat Who Is Losing Weight

If your cat’s losing weight, treatment depends on the underlying cause.  

Often, medication or a diet change can treat the underlying condition and help your cat gain back some of the weight they lost.  

Once a cat reaches 7 years of age, it’s best to increase routine vet visits from once a year to twice a year. 

This helps your vet catch underlying conditions sooner and helps keep your pet from losing weight in the first place. This also helps you closely monitor your cat’s weight, as the vet’s office will weigh them at each visit.