Common Causes of Unexplained Weight Loss in Pets

Several conditions can cause pets to lose weight unintentionally. Some of the most common include:

Hyperthyroidism

Common in cats, rare in dogs, hyperthyroidism occurs when the thyroid gland produces too much hormone, causing the body’s metabolism to speed up. This can lead to:

• Weight loss despite a normal or increased appetite
• Diarrhoea
• Increased activity levels (even hyperactivity)
• Changes in behaviour, including aggression
• Occasionally, increased breathing rate

You may even feel a small lump in your cat’s neck where the thyroid gland is enlarged.

Diagnosis and Treatment: After a full physical examination, we may recommend a blood test to measure thyroid hormone levels. Sometimes, additional tests are needed to confirm the diagnosis. Thankfully, treatment options are highly effective and include medication, surgery, or even radiotherapy.

Chronic Kidney Disease (CKD)

This condition involves the gradual decline of kidney function and is especially common in older cats and dogs. Alongside weight loss, signs can include:

• Increased thirst
• More frequent urination
• Poor coat condition
• Lethargy

Kidney disease is progressive, but early diagnosis allows us to manage it more effectively. 

Cancer

Cancer is a word no pet owner wants to hear, but it’s an unfortunate reality, particularly as pets age. Cancer can affect almost any organ and may go unnoticed until weight loss becomes apparent. In many cases, weight loss is one of the first symptoms.

Early detection is key. Regular health checks and senior pet assessments can help us pick up on changes early when treatment options are more effective.

Digestive Disorders

Several issues affecting the digestive system can lead to poor absorption of nutrients, even if your pet is eating well. These include:

• Exocrine Pancreatic Insufficiency (EPI): Where the pancreas doesn’t produce enough digestive enzymes.
• Inflammatory Bowel Disease (IBD): An allergic or inflammatory condition that interferes with the body’s ability to absorb nutrients from food.
• Food intolerances: These can cause chronic gut inflammation or discomfort, impacting digestion.

If your pet is losing weight and also has diarrhoea, gas, or bloating, a digestive disorder could be to blame.

What You Should Do Next

The most important thing to remember is this: if your pet is losing weight without any clear reason, don’t wait. The sooner we investigate, the better the outcome is likely to be.

At HIGHlands Veterinary Hospital, we’re passionate about early intervention. Whether it’s a blood test, urine sample, ultrasound, or a change in diet, we’ll help guide you through the next steps with care, compassion, and clear communication.

When to Book a Check-Up

Give us a call if you notice any of the following:

• Your pet has lost weight despite eating well
• There’s been a change in appetite or toilet habits
• Your pet seems more lethargic or hyperactive than usual
• You just have a “gut feeling” something’s not right

Trust your instincts — you know your pet best.

Take Action Today

If you’re concerned about your pet’s weight or want to book a wellness check, get in touch with us at HIGHlands Veterinary Hospital. You can also explore our wellness and diagnostics services to see how we can support your pet’s health at every life stage.

Your pet’s wellbeing is our priority — and every kilo tells a story.