What does it mean if my diabetic dog ‘rebounds?’

There can be times when a diabetic dog’s blood sugar reading is unexpectedly high, even though they’re on insulin. We learned that this can sometimes be caused by the Somogyi effect, also known as “rebound hyperglycemia.”

What is the Somogyi Effect?

The Somogyi effect happens when a dog’s blood sugar drops too low (hypoglycemia) after receiving insulin. In response, the body tries to protect itself by releasing natural “rescue” hormones like glucagon, cortisol, epinephrine, and growth hormone. These hormones tell the liver to release stored glucose, causing blood sugar to swing back up — sometimes too high.

The result is a confusing picture: even though the dog is receiving insulin, their blood sugar looks elevated when measured later. This rebound effect can make it seem like the insulin dose is too low, when in fact, it might be too high.

All of this can make managing a diabetic dog’s blood glucose levels especially complicated. Our vet seems to think it happens rarely, and it could be confused with the “Dawn Phenomenon,” when diabetic dogs have unusually high readings in the morning. <LINK>>

Why does it happen?

We’ve learned that several factors can trigger the Somogyi effect in dogs:

• Too much insulin was given.
  
• The insulin lasted longer than expected, causing a late drop.
  
• Meals or snacks were missed or not timed properly with the insulin dose.
  
• Increased activity or stress led to lower blood sugar than usual.
  

Because it’s the body’s protective mechanism, the Somogyi effect is unpredictable and can be tricky to spot without careful monitoring.

Signs to watch for

You might suspect the Somogyi effect if:

• Your dog has unusually high glucose readings despite insulin.
  
• There’s a pattern of high morning blood sugar but no obvious reason. In our experience, it’s worth ruling out the Dawn Phenomenon <<LINK>> with a blood glucose curve. Unfortunately, this could mean a late night and very early morning to get all the readings. My partner and I split the duties so that we both get a semi-decent night’s sleep.
  
• Your dog shows signs of hypoglycemia (weakness, shaking, disorientation) that later shift to symptoms of high blood sugar (increased thirst, urination, tiredness).
  

On a glucose curve, the Somogyi effect often shows as a sharp dip into low blood sugar, followed by a sudden rebound rise. Here’s some advice on how to run a glucose curve. <<LINK>>

How it’s different from the Dawn Phenomenon

The Somogyi effect is sometimes confused with the dawn phenomenon, but the causes are very different:

• Somogyi effect = rebound from a low caused by insulin.
  
• Dawn phenomenon = a natural early-morning rise in blood sugar caused by hormones, not a rebound.
  

This distinction matters, because the treatment approach is opposite: increasing insulin may help with the dawn phenomenon, but it can make Somogyi rebound worse.

What to do if you suspect it

If you think the Somogyi effect may be happening:

• Do not change insulin doses on your own.
  
• Record blood sugar readings carefully throughout the day and night, especially overnight when hidden lows may occur.
  
• Share your records with your veterinarian. They may recommend a detailed glucose curve or continuous glucose monitoring to catch these swings.
  
• Your vet may adjust the dose, timing, or type of insulin to prevent future drops and rebounds.
  

The bottom line

The Somogyi effect is the body’s way of overcorrecting a low blood sugar, leading to unexpected highs. For diabetic dogs, this can make insulin management tricky, but with close monitoring and veterinary guidance, it can be identified and corrected.

If your dog’s blood sugar seems confusingly high despite insulin, don’t assume they need more insulin — sometimes they actually need less. Work with your vet to untangle the pattern and find the safest plan for your pup.