Low blood sugar, or hypoglycemia, happens when glucose in your bloodstream drops below about 70 mg/dL. The causes range from medication side effects and missed meals to rare medical conditions, and the reason matters because different triggers call for different responses. Whether you have diabetes or not, understanding what drives blood sugar down helps you recognize patterns and prevent it from happening again.
How Your Body Normally Keeps Blood Sugar Stable
Your body treats blood sugar like a thermostat. After you eat, glucose enters your bloodstream and your pancreas releases insulin to move it into cells for energy. Between meals, your liver acts as a backup generator, releasing stored glucose (glycogen) and manufacturing new glucose from raw materials like amino acids and lactate. Hormones from the adrenal and pituitary glands fine-tune this system, signaling the liver to release more glucose when levels start dipping.
Hypoglycemia occurs when something disrupts this balance: too much insulin pulls glucose out of the blood too fast, the liver can’t keep up with demand, or stored fuel runs out. The specific disruption depends on your health, medications, and what you’ve eaten or not eaten recently.
Diabetes Medications Are the Most Common Cause
If you have diabetes, the most frequent trigger for low blood sugar is the medication you take to manage it. Insulin is the biggest culprit, but several oral medications can also push glucose too low. These include sulfonylureas (glipizide, glimepiride, glyburide), glinides, and sometimes SGLT2 inhibitors when combined with sulfonylureas. The underlying problem is straightforward: these drugs lower blood sugar by design, and sometimes they lower it too much.
The situations that tip the balance are predictable. Taking your usual dose but eating less than normal, skipping a meal, or miscounting carbohydrates can leave too much insulin circulating relative to the glucose available. Getting more physical activity than usual burns through glucose faster. Drinking alcohol compounds the problem because it impairs your liver’s ability to release glucose as a safety net. Any combination of these factors raises the risk further.
Exercise and Delayed Blood Sugar Drops
Physical activity doesn’t just burn glucose in the moment. After a workout, your muscles need to replenish their glycogen stores, which pulls glucose from your bloodstream for hours afterward. On top of that, your body becomes more sensitive to insulin after exercise, and this heightened sensitivity can last 24 to 48 hours. That means a blood sugar drop can show up well after you’ve finished exercising, sometimes in the middle of the night following an active afternoon.
If you don’t eat enough carbohydrates in the hours after sustained exercise, your body may not have enough incoming glucose to refuel muscles and keep blood levels stable at the same time. This is why late-onset hypoglycemia after exercise catches people off guard: the activity feels fine in the moment, but the metabolic aftermath plays out over a full day or two.
Reactive Hypoglycemia After Meals
Some people experience low blood sugar within four hours of eating, a pattern called reactive (or postprandial) hypoglycemia. In people with diabetes, this can result from insulin or medication kicking in harder or later than expected relative to a meal. In people without diabetes, the cause is often unclear, though it tends to be linked to what and when you eat. Meals high in refined carbohydrates can trigger a surge of insulin that overshoots the amount of glucose available, causing a sharp drop a few hours later.
Alcohol and Liver Function
Your liver is the organ responsible for keeping blood sugar from falling too low between meals. It does this partly through gluconeogenesis, a process of building new glucose molecules. Alcohol directly interferes with this process. In one study of overnight-fasted men, alcohol reduced gluconeogenesis by 45% and cut the liver’s overall glucose output by 12% compared to a placebo. The availability of raw materials the liver uses to make glucose dropped by 61%.
This matters most when you drink heavily without eating. The liver gets tied up processing alcohol and can’t do its usual job of feeding glucose into your bloodstream. The effect is temporary, but it can be significant enough to cause symptoms, especially overnight or in the early morning after a night of drinking.
Medical Conditions That Lower Blood Sugar
In people who don’t have diabetes and aren’t taking blood sugar-lowering medications, persistent hypoglycemia usually points to an underlying medical issue. Several organ systems can be involved:
- Liver disease: Severe hepatitis, cirrhosis, and other serious liver conditions impair the organ’s ability to store and release glucose. Since the liver is your primary defense against falling blood sugar, significant liver damage removes that safety net.
- Kidney disease: The kidneys help clear medications from your body. When they’re not functioning well, drugs that lower blood sugar can build up to higher-than-intended levels. Kidney disease can also directly affect glucose metabolism.
- Adrenal or pituitary disorders: These glands produce hormones that tell the liver when to release glucose. If they’re underperforming due to tumors or other problems, the counter-regulatory response that normally prevents blood sugar from dropping too low doesn’t kick in properly.
- Critical illness: Severe infections, advanced heart disease, and sepsis increase the body’s glucose demands while simultaneously impairing the systems that supply it.
Insulinomas and Insulin Overproduction
A rare but important cause of unexplained low blood sugar is an insulinoma, a small tumor in the pancreas that secretes insulin regardless of whether blood sugar is high or low. Because insulin’s entire job is to pull glucose out of the blood, a constant drip of excess insulin leads to repeated episodes of hypoglycemia, often during fasting or between meals. Other unusual pancreatic cell growths can produce insulin-like substances with the same effect.
Doctors suspect an insulinoma when blood sugar drops below 40 mg/dL while insulin levels remain inappropriately high. The diagnostic workup involves measuring insulin, a related molecule called C-peptide, and proinsulin during a supervised fasting period. Most insulinomas are benign and can be surgically removed.
Non-Diabetes Medications That Can Cause It
Diabetes drugs aren’t the only medications that lower blood sugar. Several other classes of drugs carry this risk. Beta-blockers used for heart conditions can mask the usual warning signs of low blood sugar (like a racing heart) while also contributing to the drop itself. Certain antibiotics, including some fluoroquinolones and trimethoprim-sulfamethoxazole, have been linked to hypoglycemia. Quinine, used to treat malaria, is another known trigger, particularly in children or people with kidney problems. Even some heart rhythm medications can cause it.
Beta-blockers deserve extra attention because they create a double problem. They can contribute to low blood sugar and simultaneously block the trembling and rapid heartbeat that would normally alert you that your glucose is falling. This makes it easier to miss the early warning signs.
What Low Blood Sugar Feels Like
The symptoms of hypoglycemia come in two waves that reflect what’s happening in your body. The first set of symptoms comes from your nervous system sounding the alarm: sweating, shaking, a pounding heart, anxiety, and intense hunger. These are your body’s stress response trying to get you to eat something and triggering the liver to release glucose.
If blood sugar continues to fall, a second, more concerning set of symptoms appears as the brain itself runs short on fuel. These include confusion, difficulty concentrating, irritability, slurred speech, blurred vision, and coordination problems that can look like intoxication. Without treatment, severe hypoglycemia can progress to seizures and loss of consciousness. The progression isn’t always linear. Some people, particularly those who experience frequent low blood sugar episodes, lose the ability to feel the early warning symptoms entirely, a condition called hypoglycemia unawareness.
How Doctors Confirm the Cause
Occasional mild blood sugar dips, especially after skipping a meal or exercising hard, are common and not necessarily a sign of a medical problem. Doctors look for a pattern called Whipple’s triad before diagnosing a true hypoglycemic disorder: you have symptoms consistent with low blood sugar, a lab test confirms low glucose at the time of symptoms, and the symptoms go away once blood sugar is raised. All three must be present.
This matters because many people experience symptoms like shakiness and anxiety that feel like low blood sugar but aren’t actually caused by it. A home glucose meter reading alone isn’t enough for diagnosis. Doctors require a laboratory blood draw taken during an episode to confirm. If Whipple’s triad is confirmed and there’s no obvious medication cause, the workup expands to look for insulinomas, hormone deficiencies, liver or kidney disease, and other underlying conditions.