Before assuming that your dog has insulin resistance, always check that the insulin is being stored correctly and given properly, as simple handling or dosing issues can cause poor control. Feeding too many snacks or treats between meals is another really common reason for treatment failure.
Most diabetic dogs can be stabilised within the first couple of months after diagnosis, and after that only occasional fine-tuning of the insulin dose is needed as long as their routine is being kept consistent. If your dog’s insulin dose seems to need changing every couple of weeks (or even more frequently) or if your dog requires a very high dose of insulin (more than 1.5 units per kg per injection), this is a sign that something else may be going on.
In most cases, ongoing poor control is linked to issues in the daily routine, such as how the insulin is stored or administered, inconsistency in diet, or the presence of other medical conditions that keep blood sugar levels elevated. True insulin resistance — where the body no longer responds properly to insulin — is uncommon and generally only suspected when all the other causes mentioned above have been ruled out.
Getting insulin right is the cornerstone of diabetes management. Even small mistakes in how it’s stored, handled, or given can make it much harder to keep your dog’s blood sugar under control. Common pitfalls include:
Incorrect storage: Insulin must be kept refrigerated; if left out or frozen it can lose effectiveness
Shaking the vial too much or too little: Insulin should mixed before use according to the label instruction. Shaking too vigorously can damage the product, while not mixing enough can lead to uneven doses
Expired insulin: Insulin that’s past its shelf life or open too long (usually >4–6 weeks depending on brand) won’t work as effectively
Wrong injection technique: Injecting into fur, muscle, or the wrong site can reduce absorption
Inconsistent timing: Injections given at different times each day disrupt blood sugar control
Inaccurate dosing: Misreading syringes, wrong syringe type (U-40 vs U-100), or faulty pens can all cause problems
Missed doses: Skipping insulin or giving extra doses by mistake can destabilise control
Mix-ups with caregivers: Family members doubling up or forgetting who gave the injection
Poor rotation of injection sites: Using the same spot repeatedly can cause scar tissue and reduce absorption
If your dog’s blood sugar levels seem unstable despite careful management, your vet may suggest repeating a blood glucose curve to rule out something called the Somogyi effect. This happens when the insulin dose is too high and causes the blood sugar to drop dangerously low. The body then reacts by releasing hormones that push the sugar back up, sometimes very high. Because it looks like poor control, owners may think more insulin is needed, but in fact the opposite is true — the dose may need to be reduced.
Your vet might also ask you to pop back into the clinic to check the technique you are using to give insulin injections.
When a diabetic dog is difficult to stabilise, we always want to check what they are actually eating since even small changes in what goes in can have big impacts on how much the blood sugar levels rise and therefore how much insulin they need to bring it under control. Common pitfalls include:
Dogs that are overweight or obese can develop insulin resistance similar to Type 2 diabetics, which makes their diabetes harder to control. Helping your dog return to a healthy weight through a careful diet and regular exercise can improve how their body responds to insulin and make blood sugar levels easier to manage
Some medications can make it harder to keep diabetes under control because they interfere with how insulin works or raise blood sugar levels. If your diabetic dog needs one of these medicines, your veterinarian will carefully adjust the treatment plan and may recommend closer monitoring.
Corticosteroids (prednisone, prednisolone, dexamethasone) – commonly used for skin disease, arthritis, or immune conditions; can raise blood sugar and cause insulin resistance
Progestagens (e.g. megestrol acetate) – used for reproductive control; significantly reduce insulin sensitivity
Hormonal changes/therapies (progesterone from intact females, growth hormone treatments, thyroid hormone at high doses) – can make blood sugar harder to stabilise
Some diuretics (e.g. thiazides) – may increase blood glucose levels
Other less common drugs (e.g. phenothiazine sedatives) – can alter glucose metabolism
Anytime you see a new veterinarian, always let them know that your dog has diabetes before starting any new medication.
Sometimes poor diabetes control isn’t about the insulin itself, but about other health problems happening at the same time. These conditions can raise blood sugar levels, make the body less responsive to insulin, or add extra stress that destabilises control.
Infections: urinary tract infections, dental disease, or skin infections can all raise blood sugar and increase insulin needs
Cushing’s disease (hyperadrenocorticism): excess cortisol makes the body resistant to insulin
Pancreatitis: inflammation of the pancreas disrupts both digestion and blood sugar control
Hypothyroidism or hyperthyroidism: thyroid hormone imbalances can affect metabolism and insulin response
Obesity: excess body fat contributes to insulin resistance
Female dogs in heat (oestrus/dioestrus): progesterone and growth hormone during this cycle can interfere with insulin effectiveness
Other systemic illnesses: liver or kidney disease can also make regulation more difficult
If your vet suspects one of these conditions, they may recommend further tests to identify and treat the underlying problem. Managing these health issues is often the key to improving blood sugar control and reducing the amount of insulin your dog needs.
If all of these possible problems have been ruled out, your veterinarian may suggest trying a different type of insulin or referring you to a veterinary internal medicine specialist for further investigation. The cost of seeing a specialist is usually around NZD $450–$500 for the initial consult, plus the cost of any additional diagnostic tests or treatments they recommend. While this may feel like a big upfront expense, it can often save money in the long run by getting to the bottom of the problem more quickly. Most importantly, it helps improve your dog’s comfort and quality of life.
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