A woman in her fifties came to the counter with her glucose meter in her handbag and a puzzled look. "When I check at bedtime it is around 110. When I wake up it is 180, and I have not even eaten yet. Am I eating too much at dinner?" This scene is a composite of several conversations, and the answer she needed was not about dinner at all.

A high reading first thing in the morning can come from two different causes, and they need different fixes. The first is the dawn phenomenon, a normal early-morning hormone rise that the body usually covers with insulin. The second is the Somogyi effect, where blood sugar dips overnight and then rebounds high. The two can look identical on a single morning reading. Telling them apart takes a little detective work, and it should be done with your diabetes team, not by changing your insulin or tablets on your own.

What the dawn phenomenon is

The Cleveland Clinic describes the dawn phenomenon as a natural increase in certain hormones in the early morning. Between about 3 a.m. and 8 a.m., the body releases cortisol and growth hormone. These prompt the liver to release more glucose. In someone without diabetes, the pancreas responds by releasing enough insulin to balance it out. In someone with diabetes, there may not be enough insulin available, so blood sugar rises.

The Cleveland Clinic states that the dawn phenomenon only affects people with diabetes, because people without diabetes make enough insulin to offset the rise. So if your morning readings run high most days, that is a sign your overnight treatment plan may need reviewing with your team.

What the Somogyi effect is

The Somogyi effect works differently. It starts with blood sugar falling too low overnight, usually because of injected insulin. The body responds with a hormone surge that pushes glucose back up, sometimes high. The result is a high morning reading that came after a low during the night. The Cleveland Clinic describes it as occurring when injected insulin lowers blood sugar too much overnight.

The difference matters because the treatment for one can make the other worse. If a low at night is the real cause and more insulin is added, the night-time lows can get deeper.

It is also worth knowing that a true Somogyi rebound seems to be less common than people think. A 2013 study in Diabetic Medicine looked at continuous glucose monitor data from 89 adults with type 1 diabetes. On nights with a low, the next morning's fasting reading was usually lower, not higher, and the authors concluded that the Somogyi effect is rare in clinical practice. That does not make overnight lows harmless. They still matter, and they still need ruling out with your team.

How to tell them apart

The most reliable way is to see what happens overnight. The Cleveland Clinic notes that a continuous glucose monitor (CGM) is especially useful here, because it shows whether any overnight lows happened. If you do not use a CGM, your diabetes team may ask you to check your blood sugar around 3 a.m. on a few nights, as well as at bedtime and on waking. A low reading at 3 a.m. followed by a high reading on waking suggests the Somogyi effect. A normal or high reading at 3 a.m., with a high reading on waking, fits the dawn phenomenon better. Your team is best placed to read the pattern.

Keep a simple log for about a week. Record the time, the reading, what you ate and drank in the evening, any alcohol, any insulin or tablets, and whether you woke with shakes or sweats. That log is worth more than memory when you sit down with your team.

Alcohol deserves a special mention. The Know Diabetes resource explains that alcohol can make hypos more likely in people on insulin or certain diabetes medicines, and that blood sugar can drop and stay low for many hours afterwards. An evening drink can therefore set up an overnight low, which can be followed by a rebound high in the morning.

Why one high reading is not a pattern

A single high morning reading can follow a late meal, a stressful evening or a broken night's sleep, and on its own it does not tell you much. Look for the pattern over several days. If most mornings run high, or the readings climb through the week, that is worth raising with your team. If you see a low reading at any time, act on it first using the low blood sugar plan your team gave you, and then tell them, because a low can be the start of the Somogyi pattern.

What counts as a good number?

The American Diabetes Association Standards of Care in Diabetes 2026 list a before-meal (preprandial) glucose goal of 80 to 130 mg/dL (4.4 to 7.2 mmol/L) for many nonpregnant adults, a peak after-meal goal below 180 mg/dL (10.0 mmol/L), and an A1C goal below 7%. Your team may set a different target for you, especially if you have had low blood sugar or other health conditions. Use the targets your team gives you, not a number from a website.

What can help, and what to discuss

Once you know which pattern you have, the fix is a conversation with your prescriber or diabetes nurse. For people who use an insulin pump, the Cleveland Clinic says adjusting the pump's early-morning basal rates (the background insulin it delivers) is often the most effective approach. For everyone else, it describes working out the best plan with your provider, which can include looking at your evening routine, your dinner and the medicines you already take.

Other practical topics to bring up include:

Evening meal timing, and whether a bedtime snack helps or hurts.
Alcohol, especially on nights before a high morning reading.
Physical activity, including the time of day you exercise.
Your sleep pattern, and whether you wake during the night.
Your target readings for fasting and after meals.

Please do not skip breakfast to lower a morning reading, and do not change your insulin or tablets to fix one number. Changes like these can make hypos more likely.

Low blood sugar: what to do

If you use insulin or certain tablets, low blood sugar is always a possibility, and the Somogyi pattern is a reason to ask about it. The NHS advice for someone awake and able to swallow is to take something that raises blood sugar quickly, such as a small glass of fruit juice or a sugary fizzy drink, or five glucose or dextrose tablets. Recheck after 10 to 15 minutes. If the reading is still below 4 mmol/L (about 70 mg/dL), have another sugary drink or snack and check again after 10 minutes. Once you feel better and your reading is above 4 mmol/L, eat something that keeps your blood sugar up for longer, such as a sandwich or your next meal if it is due. If someone cannot swallow safely or is unconscious, do not give food or drink, place them in the recovery position, and give a glucagon injection if one is available and you know how to use it. Call 999 (UK) or 911 (US) if glucagon is not available, if they have not recovered within 10 minutes of it, or if they have been drinking alcohol.

Questions to ask your doctor or pharmacist

Do my readings look more like the dawn phenomenon or the Somogyi effect?
Should I use a CGM, and can you help me set it up?
Do my insulin or tablets need to change, and who should make that change?
Could my evening meal, bedtime snack or alcohol be part of the problem?
What fasting and after-meal targets should I aim for?
What should I do if I have a low reading at night?

Frequently asked questions

Is a high morning reading normal?

In people without diabetes, the pancreas usually releases enough insulin to offset the early-morning hormone rise. For people with diabetes, a consistently high morning reading is worth reviewing with the care team, because it may mean overnight cover needs adjusting.

Should I check at 3 a.m.?

Only if your team asks you to. A few overnight checks can show whether a low is happening. Do not set an alarm and make changes on your own. The results need interpreting by someone who knows your medicines.

Can I just eat less in the evening?

Evening meals matter, but cutting food without advice can cause problems if you take insulin or tablets. Talk to your team first. A dietitian can help you plan meals that work with your medicines.

Why is my bedtime reading fine but my morning reading high?

This pattern fits the dawn phenomenon, but it can also happen with the Somogyi effect if an overnight low is followed by a rebound. A CGM or overnight checks are the simplest way to tell which is happening.

If you'd like the full guide, my book The Type 2 Diabetes Food List and Meal Plan explains what to eat and gives a plain-English look at how common diabetes medicines work, so you can ask better questions at your next appointment.

Sources

Cleveland Clinic. Dawn phenomenon
Choudhary P, Davies C, Emery CJ, Heller SR. Do high fasting glucose levels suggest nocturnal hypoglycaemia? The Somogyi effect: more fiction than fact? Diabetic Medicine. 2013;30(8):914-917.
Know Diabetes (NHS West and North London). Alcohol and hypos
American Diabetes Association Professional Practice Committee. 6. Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes 2026. Diabetes Care. 2026;49(Suppl 1):S132-S149.
NHS. Low blood sugar (hypoglycaemia)
NHS. High blood sugar (hyperglycaemia)