Hyperglycemia and hypoglycemia in type 2 diabetes

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If someone has diabetes that isn’t treated properly, they have too much sugar in their blood (hyperglycemia). Too little sugar in the blood (hypoglycemia) is usually a side effect of blood-sugar-lowering medication.

Diabetes is a metabolic disease in which there's a problem with insulin (a hormone). It can affect your health in many ways. In type 2 diabetes, the insulin that is released into the bloodstream is no longer effective enough. In type 1 diabetes, on the other hand, the body only produces very little insulin – or none at all.

When is blood sugar considered to be too high or too low?

It is completely normal for your blood sugar levels to go up and down every day in response to the food you eat. Between around 60 and 140 milligrams of sugar per deciliter of blood (mg/dl) is considered to be normal in people who don’t have diabetes. This is equivalent to a blood sugar concentration of between 3.3 and 7.8 mmol/l. “Millimoles per liter” (mmol/l) is the unit that blood sugar is measured in. It describes the amount of sugar molecules per liter.

If someone has readings over 7.8 mmol/l (140 mg/dl), they are considered to have high blood sugar (hyperglycemia). Left untreated, type 1 diabetes can lead to blood sugar levels of over 27.8 mmol/l (500 mg/dl). Such high levels tend to be uncommon in type 2 diabetes.

People with blood sugar levels below 3.3 mmol/l (60 mg/dl) are considered to have low blood sugar (hypoglycemia). But, as you can see in the illustration below, there are no clear-cut borders between normal blood sugar levels and too high or too low blood sugar.

Illustration: Blood sugar: Normal range between hyperglycemia and hypoglycemia, as described in the article

What are the signs of hyperglycemia?

High blood sugar levels mainly occur if there isn't enough insulin or the insulin doesn't work properly. Without the effect of insulin, the organs can't make good use of the sugar in the blood, so the sugar builds up.

Hyperglycemia doesn't always have immediately noticeable effects. Someone might have it for years without having any physical symptoms. But very high blood sugar can cause the following symptoms:

  • Extreme thirst
  • Frequent urination
  • Tiredness
  • Listlessness
  • Nausea
  • Dizziness

If someone has extremely high blood sugar levels, they may feel confused and drowsy or even lose consciousness (diabetic coma).

High blood sugar: What now?

If you have the above symptoms over a long period of time or if they keep occurring, it's important to see a doctor. They could be a sign of diabetes.

If these symptoms occur in people who have already been diagnosed with diabetes, they could be a sign that the treatment is no longer effective enough. Then medication can be prescribed or adjusted to make your blood sugar levels go back down. You may stay at the hospital while your blood sugar levels are being stabilized.


If you are feeling drowsy, confused or lose consciousness, the emergency services should be called (112 in Germany and many other countries, 911 in the U.S.).

What are the signs of hypoglycemia?

Low blood sugar is most common in people who use insulin or take certain tablets to reduce high blood sugar. This is because things like unexpected physical activity, eating too little food or drinking too much alcohol can mean that you need less insulin than you thought, causing your blood sugar to drop too low.

Signs that your blood sugar is too low may include:

  • Racing pulse
  • Cold sweats
  • Pale face
  • Headache
  • Feeling very hungry
  • Shivering, feeling weak in the knees
  • Feeling restless, nervous or anxious
  • Difficulty concentrating, confusion

The severity of these symptoms depends on the blood sugar levels and can vary from person to person. The symptoms don’t occur all at once. If you aren’t sure whether your blood sugar is too low, you can measure it to make sure.

Your blood sugar levels may also drop at night, making you feel tired and weak in the morning.

Mild hypoglycemia doesn't usually have any serious health effects. But severe hypoglycemia can lead to a loss of consciousness and become life-threatening.

Low blood sugar: What now?

It is important to react quickly enough and eat or drink something, like dextrose sugar or a sugary drink (no "diet" or "zero" soft drinks with artificial sweeteners!).

If someone has severe hypoglycemia they may feel drowsy and confused, and might even become unconscious. People who have type 1 diabetes often carry a pre-filled syringe on them in case that happens, containing the hormone glucagon. Glucagon makes the liver release sugar into the bloodstream. Someone else can then inject the hormone if necessary. If this is not possible, it’s important to call the emergency services immediately (112 in Germany and many other countries, 911 in the U.S.) and ask for medical help.

If your blood sugar levels keep on dropping too low, you should see your doctor. It could then be a good idea to change your lifestyle or medication.

Bundesärztekammer (BÄK), Kassenärztliche Bundesvereinigung (KBV), Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF). Nationale Versorgungsleitlinie: Therapie des Typ-2-Diabetes. S3-Leitlinie. AWMF-Registernr.: nvl-001g. 2023.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on December 18, 2023

Next planned update: 2026


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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