Low blood sugar, or hypoglycemia, happens when your blood glucose drops below 70 mg/dL. Below 54 mg/dL is considered severe. The causes range from medication side effects and skipped meals to hormonal disorders and organ disease, and they differ depending on whether you have diabetes.
Diabetes Medications Are the Most Common Cause
Insulin is the most frequent culprit. If you take more insulin than your body needs for the amount of food you’ve eaten or the activity you’ve done, your blood sugar can plummet. This happens when you miscalculate a dose, skip a meal after injecting, or exercise harder than expected without adjusting your insulin.
A class of oral diabetes drugs called sulfonylureas also carries significant risk. These medications work by stimulating your pancreas to release more insulin, and they do so regardless of what your blood sugar is at that moment. That makes them less precise than some newer medications. The risk climbs when sulfonylureas are combined with other drugs that also lower blood sugar, including certain antibiotics, anti-inflammatory painkillers, and blood thinners, all of which can amplify the blood-sugar-lowering effect.
Timing matters too. Taking your usual dose but eating less than normal, delaying a meal, or drinking alcohol alongside these medications can tip the balance toward a dangerous drop.
Low Blood Sugar Without Diabetes
You don’t need a diabetes diagnosis to experience hypoglycemia. The most common pattern in people without diabetes is called reactive hypoglycemia, where blood sugar drops within four hours after eating. The exact mechanism isn’t always clear, but it’s thought to involve your body releasing too much insulin in response to a meal, especially one high in refined carbohydrates. The surge of insulin overshoots what’s needed, pulling your blood sugar below normal range.
Reactive episodes tend to cause shakiness, sweating, lightheadedness, and irritability that improve quickly once you eat something. If this happens to you regularly, tracking what you eat and when symptoms appear can help identify a pattern.
How Alcohol Blocks Your Liver’s Safety Net
Your liver acts as a glucose reservoir. When blood sugar starts to fall, the liver normally converts stored glycogen into glucose and releases it into your bloodstream. During longer fasts, it can also manufacture new glucose from raw materials like amino acids and lactate, a process called gluconeogenesis.
Alcohol disrupts both of these rescue mechanisms. When your liver is busy processing alcohol, it generates a byproduct that interferes with the chemical reactions needed to produce new glucose. Alcohol also switches off the genes responsible for glucose production in liver cells, essentially silencing the liver’s ability to respond to falling blood sugar. This is why drinking on an empty stomach, or drinking heavily without eating, is particularly dangerous. The risk is highest several hours after drinking, sometimes while you’re asleep, which is why alcohol-related hypoglycemia can catch people off guard.
Hormonal Deficiencies
Several hormones work together to keep blood sugar from dropping too low. Cortisol, produced by the adrenal glands, is one of the most important. It signals the liver to produce glucose and helps your body access stored energy. When the adrenal glands don’t produce enough cortisol, a condition called adrenal insufficiency (Addison’s disease in its primary form), your body loses a critical defense against low blood sugar.
Adrenal insufficiency can be caused by autoimmune damage to the adrenal glands themselves, problems with the pituitary gland that controls them, or, most commonly, from long-term use of steroid medications like prednisone. When you take synthetic steroids for weeks or months, your body dials down its own cortisol production. If you stop the medication abruptly, your adrenal glands can’t ramp back up quickly enough, leaving you vulnerable to hypoglycemia and other serious symptoms.
Growth hormone deficiency and thyroid disorders can also impair the body’s glucose regulation, though they are less common triggers on their own.
Liver and Kidney Disease
Because the liver plays such a central role in maintaining blood sugar, advanced liver disease is a significant cause of hypoglycemia. In cirrhosis, healthy liver tissue is gradually replaced by scar tissue, reducing the organ’s ability to store glycogen and produce new glucose. Multiple factors pile up: the liver has fewer functioning cells, muscle wasting limits the raw materials available for glucose production, and poor nutrition (common in advanced cirrhosis) means glycogen stores are chronically low.
Severe kidney disease contributes in a different way. The kidneys help clear insulin and other blood-sugar-lowering medications from the body. When they’re not working well, these drugs stay active longer than intended, which can cause prolonged or unexpected drops in blood sugar. The kidneys also play a small but real role in producing glucose themselves, so advanced kidney failure removes that backup source.
Insulinoma: A Rare but Treatable Tumor
An insulinoma is a rare tumor in the pancreas that produces excess insulin regardless of what your blood sugar is doing. Because the insulin release is constant and unregulated, it can cause repeated episodes of hypoglycemia, often with no obvious trigger. Symptoms tend to be worst during fasting, such as before breakfast or after skipping a meal.
About 85% to 90% of insulinomas are benign and don’t spread beyond the pancreas. Doctors suspect one when a patient has what’s known as Whipple’s triad: symptoms of low blood sugar, a confirmed blood glucose reading below 55 mg/dL, and improvement after eating carbohydrates. The gold-standard diagnostic test is a supervised 72-hour fast, during which doctors monitor blood sugar, insulin levels, and related markers. Once confirmed, imaging with CT, MRI, or endoscopic ultrasound locates the tumor, and surgical removal is usually curative.
Stomach Surgery and Other Causes
Gastric bypass and other bariatric surgeries can cause low blood sugar by changing how quickly food moves through your digestive system. After these procedures, food (especially sugar) reaches the small intestine much faster than normal. This rapid delivery triggers an exaggerated insulin response, which can then overshoot and cause hypoglycemia, typically one to three hours after eating. The pattern often resembles reactive hypoglycemia but tends to be more pronounced.
Other less common causes include inherited metabolic disorders that affect how your body processes sugars, prolonged intense exercise without adequate fueling, severe infections (which increase the body’s glucose demands), and certain non-diabetes medications that happen to lower blood sugar as a side effect.
Recognizing and Treating a Low
Early symptoms of low blood sugar include shakiness, sweating, a fast heartbeat, hunger, irritability, and feeling anxious or lightheaded. As blood sugar drops further, you may experience confusion, blurred vision, difficulty speaking, or trouble concentrating. Severe hypoglycemia, below 54 mg/dL, can cause seizures or loss of consciousness.
The standard approach is the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates (about four glucose tablets, half a cup of juice, or a tablespoon of honey), then wait 15 minutes and recheck your blood sugar. If it’s still low, repeat. Once it returns to normal, eat a small snack or meal to keep it stable.
For severe episodes where you can’t swallow safely or lose consciousness, glucagon is the emergency treatment. It’s available as a premixed injection pen (similar to an epinephrine auto-injector), a nasal powder, or a kit that requires mixing. The ready-to-use pen and nasal powder are preferred because they don’t require preparation during a crisis. If you’re at risk for severe lows, keeping glucagon accessible and making sure the people around you know how to use it can be lifesaving.