The Somogyi effect is rebound high blood sugar caused by overnight lows. It's controversial — some researchers question whether it exists in modern insulin users — but it's worth understanding.
How it happens
- You take too much insulin (or eat too little) before bed
- Glucose drops dangerously low around 2–3 AM
- Your body releases cortisol, glucagon and adrenaline to rescue glucose
- By morning, you're high — sometimes very high
How to tell vs the dawn phenomenon
Both cause morning highs.
| Somogyi | Dawn phenomenon | |
|---|---|---|
| Pre-bed glucose | Normal/low | Normal |
| 3 AM glucose | Low (under 70) | Normal/rising |
| Morning glucose | High | High |
| Cause | Overnight low | Cortisol rise |
| Fix | Lower bedtime insulin | Different — see other article |
How to test for it
Set an alarm for 3 AM for three nights and check glucose. If you're consistently below 70 mg/dL, Somogyi is likely. If you're already rising, dawn phenomenon is more likely.
What to do
- Lower your bedtime long-acting insulin slightly (talk to your doctor)
- Add a small protein/fat snack at bedtime
- Switch to a flatter long-acting insulin if you're on NPH
- Consider a CGM for overnight visibility
Why some experts doubt it
Modern long-acting insulins (glargine, degludec) have flatter profiles than older NPH. Documented rebounds are rarer with newer drugs. But for anyone still using NPH or with erratic schedules, the pattern is real.