The biggest immediate danger with insulin is giving too much. If you’re ever unsure whether your dog received an insulin dose or if they ate their meal properly, it’s safer to skip the dose and call your vet for advice. Low blood sugar (hypoglycaemia) can become life-threatening within minutes, whereas spending a few extra hours with higher blood sugar (hyperglycaemia) will usually not cause your dog any serious long term problems.
All diabetic dogs need regular insulin injections, usually every 12 hours, because their bodies can no longer make enough insulin to keep blood sugar under control. In this section, we’ll explain how insulin normally works in healthy dogs and how insulin therapy is designed to copy that process. This background will help you better understand your veterinarian’s recommendations about what type of insulin to use, when to give it, and how much to give. We’ll also cover practical tips on storing insulin, giving injections safely, and troubleshooting common problems so you can feel confident managing your dog’s treatment at home.
The goals of managing canine diabetes are a little different from those in people. In human medicine, treatment often involves using multiple types of insulin and adjusting doses meal by meal to keep blood glucose levels within a very tight range. For dogs, this level of fine-tuning is not practical or necessary – we just need to achieve “good enough” control through a routine that owners can realistically manage every day.
With insulin therapy in dogs, our main priority is to control the clinical signs of high blood sugar (excessive urination, thirst, and hunger) while avoiding dangerous lows (hypoglycaemia). This usually means aiming for blood glucose values within an acceptable range across the day, rather than perfect numbers at every moment. For most dogs, having a nadir (lowest blood glucose value during the day) between 100-150 mg/dL (5.5-8.3 mmol/L) and an average blood glucose level of ≤250 mg/dL (≤13.9 mmol/L) is considered satisfactory.
In general, we would rather have their blood sugar levels be slightly too high than risk much more serious complications from having their blood sugar level be too low.
Insulin is the hormone that acts like a key, moving glucose from the bloodstream into the body’s cells for energy. In dogs with diabetes, their bodies can’t make enough insulin, so we use injections to copy this process. The tabs below explain how insulin normally works, how insulin therapy helps, and what can happen when dosing is not quite right (the Somogyi effect).
In a non-diabetic dog or person, the pancreas continuously releases low levels of insulin even when we’re not eating (called basal insulin secretion). This steady insulin release is important for maintaining steady blood glucose levels between meals and overnight by:
When we eat, the pancreas releases extra insulin to help move glucose from the bloodstream into the body’s cells. The natural insulin our body produces works very quickly and is broken down very quickly, which allows the pancreas to fine-tune the amount released so it closely matches how fast glucose from the meal is entering the bloodstream.
This helps keep blood glucose levels within the normal range of about 80–120 mg/dL (4.4–6.6 mmol/L), although they can sometimes rise to 140–160 mg/dL (7.7–8.8 mmol/L) after meals before returning to baseline.
For diabetes management in people, they will often give a long-acting, slow-release insulin once or twice daily to copy the body’s baseline insulin secretion (basal insulin injections) and then use a short-acting, quick-release insulin around mealtimes to handle the sharp increases in blood glucose levels (bolus insulin injections). The dose of the bolus insulin injections can be adjusted to match the expected carbohydrate content of the meal, which is important because we tend to have much more variability in the types of foods we eat at each meal.
For diabetes management in dogs, we most commonly give twice-daily injections of an intermediate-acting insulin. This approach works well because dogs typically eat regular meals twice a day, usually with the same type of food, allowing us to time insulin injections with feeding to help manage post-meal glucose spikes. While this method doesn’t offer the same level of fine-tuned control as using separate basal and bolus insulins as is done in human diabetes care, it requires much less intensive management, making it a far more practical and sustainable option for most dog owners.
The following graphs shows what we are ideally looking for with how blood glucose levels respond to insulin:
Dogs start spilling sugar into their urine once blood sugar gets too high, and this is what drives the constant thirst and heavy urination. If we can keep your dog’s blood sugar below about 180–220 mg/dL (≈10–12 mmol/L) for much of the day, that’s usually enough to stop the sugar spillover and bring the drinking and peeing back under control, even if the numbers aren’t in the normal range.
Once insulin is injected, it keeps working to move glucose into cells no matter what the blood sugar level is doing — there’s no “off switch.” This is why it is so important to keep meals consistent (to provide glucose supply), exercise steady (to manage glucose demand), and to be aware of illnesses or stressors that can alter glucose metabolism and insulin effectiveness.
The Somogyi effect (also called rebound hyperglycaemia) occurs when an insulin injection drives blood sugar too low, often around the time of its peak effect. To protect itself, the body responds by releasing hormones that cause a massive release of glucose, often pushing the blood glucose levels much higher than normal.
The danger is that if blood sugar is measured only after this rebound, it can look like the insulin dose is too low and lead to an unnecessary increase, which makes the problem even worse. This is why dose changes should never be based on a single high reading – a full blood glucose curve is needed to check what is really happening.
Most dogs are started on intermediate-acting Vetsulin® (lente insulin) as the first choice for therapy. This insulin is a suspension containing two forms (35% amorphous and 65% zinc crystalline), which provides a quick rise in insulin activity to control the post-meal blood sugar spike, followed by a slower, more gradual release to keep levels steadier through the day.
Vetsulin® is available in two formats: a traditional vial (used with syringes) and a pre-filled pen device. Both contain the same insulin, but some owners find the pen easier and more convenient to use, while others prefer the flexibility and lower cost of vials with syringes. Your veterinarian can help you decide which option best fits your dog’s needs and your comfort with giving injections.
For larger dogs where cost is a major concern, some veterinarians may instead use Neutral Protamine Hagedorn (NPH) insulin, a human insulin available under brand names such as Humulin N® and Novolin N® as well as in generic form. NPH is the least expensive option and can work for some dogs, although it is not always as effective as Vetsulin.
Different insulins come in different concentrations, and it’s critical to match the right syringe to the right insulin. Vetsulin® is a U-40 insulin (40 IU per mL) and must be given with U-40 syringes. NPH is a U-100 insulin (100 IU per mL) and must be given with U-100 syringes. Using the wrong syringe will result in a serious dosing error, either giving far too much or far too little insulin. Always double-check that your syringes match the insulin type your dog is prescribed.
Most dogs will receive insulin injections twice daily (every 12 hours) around the same time as they are being fed their main meals. This might, for example, be 6:30am and 6:30pm or 7:00am and 7:00pm – try to pick a time that will generally suit your schedule most days. It’s really important to give the insulin injections as close to 12 hours apart as you can, but it’s okay if you’re occasionally up to an hour early or an hour late.
If there is no practical way for you to manage twice-daily injections, some dogs can be treated with once-daily insulin instead. However, this is generally less effective because the insulin doesn’t last long enough to cover the full 24 hours, and blood glucose levels may be poorly controlled for part of the day. For this reason, once-daily dosing is usually considered a fallback option when twice-daily dosing is not possible.
From a biology standpoint, the ideal timing is to give insulin about 30 to 60 minutes before a meal. This allows time for the insulin to start being absorbed and “ready to work” just as glucose from the meal begins entering the bloodstream. However, in real life, most vets recommend giving insulin just after meals. This safer approach ensures that if your dog refuses food or vomits, you haven’t given a full insulin dose without any calories to balance it, which could otherwise trigger dangerous hypoglycaemia.
The usual starting insulin dose for newly diagnosed diabetic dogs is 0.25 U/kg every 12 hours if using Vetsulin® (lente insulin), or 0.5 U/kg every 12 hours if using NPH (Neutral Protamine Hagedorn) insulin, always rounded to the nearest whole unit.
Finding the right dose takes time and careful adjustment. Usually on the first day starting insulin, your vet will check how it’s working with a blood glucose curve, which measures sugar levels at different points across the day. Based on the results and how your dog is feeling, the dose may be increased or decreased slightly (usually by ~10% to 25%). Each adjustment is followed by about 7 days at the new dose to let your dog’s body settle before the next curve is done to check how well it’s working. Some owners learn how to do blood glucose curves at home to save extra trips to the vet. This step-by-step approach is repeated until the curve looks relatively normal and your dog’s signs (thirst, urination, hunger, energy) are well controlled. For most dogs, it usually takes about 4–6 weeks to find the ideal dose and routine.
There are a number of situations where your dog’s insulin dose may need to be changed after the initial stabilisation:
Their blood glucose curve shows problems or there are signs of hypoglycaemia
Their clinical signs return – including increased thirst, urination, weight loss, or appetite changes
Other factors affect how their body uses insulin, such as:
Infection or illness
Changes in diet, weight, or exercise
Starting new medications
Dose changes are always made in small steps (about 10%), and your dog’s blood glucose curve will usually be rechecked after 5–7 days to asses how well the new dose is working. Always work with your veterinarian when adjusting the dose — frequent self-tweaks can make things worse rather than better. If you are monitoring blood glucose levels at home, we do not recommend changing the dose based on a single high reading in case it is related to the Somogyi Effect (rebound hyperglycaemia). However, if you get a low blood sugar reading (hypoglycaemia), skip the next insulin dose and contact your vet about how much to reduce it.
Proper storage is essential to make sure your dog’s insulin stays effective. Insulin that gets too warm, freezes, or is handled incorrectly can lose its strength, which means your dog’s diabetes may not be well controlled even if you’re giving the right dose.
Keep it in the fridge (2–8 °C / 36–46 °F) ideally in the fridge door where the temperature is more stable. Do not freeze.
Avoid heat and sunlight — never leave insulin in a hot car, near a heater, or on a sunny windowsill.
Mix according to label directions:
Vetsulin®: shake vigorously the first time the bottle is opened, then shaken hard enough each time it’s used to keep it looking milky
Other insulins: gently roll or tip the vial to mix to avoid damaging the insulin
Check before use — insulin should look clear (or evenly cloudy if that type of insulin requires mixing). If you see clumps, crystals, or changes in colour, do not use it.
Watch expiry dates — once opened, most insulins should be discarded after 4–6 weeks.
Store upright — especially pens and cartridges, to prevent leakage.
Some owners like to use insulin vial protectors to stop the bottle from breaking if they are accidentally knocked over.
Using a clear step-by-step checklist and good technique helps ensure your dog always receives the correct insulin dose safely and consistently. The needles are very small, and most dogs barely notice the injections once you get into a routine, quickly learning to tolerate the process well.
Here are few things to check before starting the process of preparing your insulin dose:
Make sure your dog has eaten their meal. If they haven’t finished their food or if they have vomited their food up, it is not safe to give the full insulin dose.
Confirm that no one else in the household has already given the insulin. In households where multiple people share responsibility for giving insulin injections, there is a higher risk of double-dosing
Make sure the insulin syringe matches the insulin type. Double-check that you are using the correct syringe type for the insulin prescribed (U-40 for Vetsulin®, U-100 for NPH).
To prepare the injection:
Wash your hands.
Take the Vetsulin® vial from the refrigerator and shake until the liquid looks evenly milky. Let foam settle.
Remove the needle cap, insert needle into vial, and turn vial upside down.
Withdraw the correct dose into the syringe.
Check for air bubbles – tap them to the top, push them out, and redraw the correct dose.
Where you give insulin injections can affect how quickly the insulin is absorbed. In people, the American Diabetes Association recommends always using the same general body area so the insulin is absorbed at a consistent speed – but not the exact same spot every time. Repeatedly injecting into one small area can cause lumps or fatty deposits under the skin. These can look unsightly and may reduce how well insulin works.
For dogs, we also recommend rotating injection sites to avoid this problem and to keep absorption more predictable. A simple rotation pattern works well alternating between right/left sides and location along the back starting from just behind the shoulder blades to just in front of the hips.
The injections should be given under the skin (subcutaneously) about 2.5–5 cm (1-2 inches) away from the spine. If your dog is wearing a continuous glucose monitor (like a Libre sensor), avoid injecting within about 2.5 cm (1 inch) of the sensor.
To give the injection:
It’s completely normal at first to feel unsure, or to worry that you might do something wrong and harm your dog. Many owners feel this way in the beginning. The good news is that if you follow your vet’s instructions, the risk of anything going seriously wrong is very low. With a bit of practice, giving insulin and watching your dog’s response will soon feel routine, and you’ll gain confidence knowing you’re helping them feel better.
Here are some of the common questions and concerns that owners often have when beginning insulin therapy for their dogs. When in doubt, it is always safer to skip a dose and contact your veterinarian for advice.
If you’re uncertain whether the full dose went in (for example, if the syringe slipped or some leaked out), do not give more insulin. It’s safer to wait until the next scheduled dose than risk an overdose.
Depending on how much your ate, you may still be able to give insulin, but monitor them closely for signs of hypoglycaemia. If they refuse their meal entirely, it’s safest to skip the dose and call your vet for advice. Refusing food could be a sign of something else going on that requires evaluation by your vet. Never give a full dose of insulin without food on board. If in doubt, it’s safe to skip a dose than risk hypoglycaemia.
An insulin overdose can cause dangerously low blood sugar (hypoglycaemia) depending on how much extra was given. Contact your vet immediately for advice. In the meantime, offer your dog some extra food or rub a small amount of honey or corn syrup on their gums if they are weak, wobbly, or having a seizure. Signs can sometimes appear 4 to 8 hours after the overdose depending on how long it takes the insulin to absorb and start working. Emergency veterinary care may be required.
Most dogs tolerate insulin injections very well, but if your dog squirms, yelps, or fights:
Make sure you’re injecting under the skin, not into muscle.
Try a different spot (behind the shoulders, mid-back, alternating sides).
Stay calm and gentle — sometimes a reassuring voice or a small treat afterwards helps build positive associations. If you feel nervous about giving injections, your dog can pick up on it and start feeling nervous themselves.
If injections consistently cause pain or distress, contact your vet to review your technique or equipment.
If you are more than an hour or so off schedule, it’s usually safer to skip that dose and wait until the next scheduled time rather than giving injections too close together. Giving insulin too soon can increase the risk of dangerously low blood sugar. If this happens often, talk to your vet about adjusting the injection schedule to better fit your routine.
When daylight saving time begins, the safest option for most diabetic dogs is to skip one insulin dose. This allows you to move the clock forward by an hour without giving two doses too close together, which could risk low blood sugar. You can still feed your dog their usual meal at the skipped dose time. When daylight saving ends, no change is needed — just keep giving injections at the normal times. Some dogs may do better with a half-dose instead of a missed dose, so check with your veterinarian if you’re unsure. If you regularly check your dog’s blood glucose before each injection, you may not need to skip a dose at all.
Advancing Animal Care through Shared Learning