Low blood sugar is not typically a sign that you have undiagnosed diabetes. In fact, diabetes is defined by the opposite problem: blood sugar that’s too high. However, low blood sugar (hypoglycemia) is extremely common in people who already have diabetes, particularly as a side effect of treatment. So the relationship between low blood sugar and diabetes is real, but it works differently than most people assume.
Why Diabetes Usually Means High Blood Sugar, Not Low
Diabetes develops when your body either can’t produce enough insulin (type 1) or can’t use insulin effectively (type 2). Both situations cause sugar to build up in your bloodstream rather than entering your cells. The hallmark diagnostic tests for diabetes all measure elevated blood sugar: a fasting glucose above 126 mg/dL, or a hemoglobin A1C of 6.5% or higher.
If you’re experiencing episodes of low blood sugar and you haven’t been diagnosed with diabetes, the cause is almost certainly something else. That said, there is one narrow exception worth knowing about. Some people in the early stages of type 2 diabetes experience what’s called reactive hypoglycemia, where blood sugar drops a few hours after eating. This happens because the pancreas overproduces insulin in a delayed response to a meal. It’s not common enough to be considered a reliable warning sign, but it does occasionally show up before a formal diagnosis.
How Diabetes Treatment Causes Low Blood Sugar
For people who already have diabetes, low blood sugar is one of the most frequent and potentially dangerous complications of treatment. It happens when medication pushes blood sugar below 70 mg/dL. The medications most likely to cause this include insulin, sulfonylureas, and glinides. Metformin, the most widely prescribed type 2 diabetes drug, generally doesn’t cause low blood sugar on its own, but it can when combined with sulfonylureas.
Several situations raise the risk of a low blood sugar episode if you’re on these medications: skipping a meal, exercising more than usual, drinking alcohol, or taking too much medication by mistake. The drop can happen quickly, and recognizing the symptoms early makes a significant difference in how easily you can correct it.
What Low Blood Sugar Feels Like
Early symptoms tend to come on fast and feel unmistakable once you’ve experienced them. They include shaking, sweating, a rapid heartbeat, sudden hunger, dizziness, and a wave of anxiety or irritability that seems to come from nowhere. Some people also notice tingling or numbness in their lips, tongue, or cheeks.
As blood sugar continues to drop, the symptoms shift from uncomfortable to alarming. You may feel weak, have trouble walking or seeing clearly, or start behaving in ways that seem strange to people around you. Confusion is common at this stage. Below 54 mg/dL, the situation becomes severe. Seizures, loss of consciousness, and fainting are all possible. At this point, you likely can’t treat yourself and need help from someone nearby.
The 15-15 Rule for Treating a Low
The standard approach is simple and worth memorizing if you or someone close to you takes insulin or other blood-sugar-lowering medications. Eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes and recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process. Keep going until your levels return to your target range, then follow up with a balanced snack or small meal that includes protein.
Good options for those 15 grams include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. Young children typically need less than 15 grams, especially toddlers and infants.
When Low Blood Sugar Becomes an Emergency
Severe hypoglycemia requires outside help. If the 15-15 rule isn’t working, if you can’t swallow safely, if you’re too confused to treat yourself, or if you lose consciousness, someone nearby needs to administer glucagon. Glucagon is a hormone that rapidly signals the liver to release stored sugar into the bloodstream. It comes in three forms: a premixed pen similar to an epinephrine autoinjector, a nasal powder, and a traditional kit that requires mixing before injection. The pen and nasal versions are ready to use immediately, which matters in a crisis.
If glucagon isn’t available, calling 911 is the right next step. Severe lows can lead to seizures or coma, so speed matters.
Other Causes of Low Blood Sugar
If you don’t have diabetes and you’re experiencing symptoms that feel like low blood sugar, several other explanations are worth exploring. Going long stretches without eating, heavy alcohol use, certain non-diabetes medications, and hormonal deficiencies can all cause hypoglycemia. Liver disease, kidney disorders, and rare insulin-producing tumors of the pancreas are less common but possible causes. Reactive hypoglycemia, where blood sugar dips two to four hours after a meal, also affects some people without diabetes and is generally managed through dietary changes like eating smaller, more frequent meals with balanced macronutrients.
Repeated episodes of low blood sugar without a clear explanation deserve medical evaluation. A blood draw taken during an episode can help pinpoint whether your glucose is genuinely dropping and, if so, what’s driving it.