Low blood glucose, or hypoglycemia, happens when your blood sugar drops below 70 mg/dL. At that level, your body starts sending warning signals. Symptoms typically don’t become noticeable until glucose falls below 55 mg/dL, when the brain begins running short on its primary fuel. The causes range from medications and missed meals to hormonal problems, organ disease, and even intense exercise.
How Your Body Normally Keeps Glucose Stable
Your liver is the central player. It stores glucose in a compact form called glycogen and releases it between meals to keep your blood sugar steady. When those stores run low, the liver can also manufacture new glucose from protein and other raw materials. Hormones coordinate the whole process: insulin pushes glucose down after a meal, while cortisol, growth hormone, and glucagon push it back up when it dips too low. Low glucose happens when something disrupts one or more of these systems.
Diabetes Medications
The single most common cause of low glucose is medication used to treat diabetes. Insulin and a class of oral drugs called sulfonylureas (such as glipizide and glyburide) are the most frequent offenders because they actively lower blood sugar regardless of what you’ve eaten. If the dose is too high, if you skip a meal, or if you exercise more than usual, these drugs can push glucose below a safe level.
Other diabetes medications raise the risk mainly when combined with sulfonylureas. Metformin on its own rarely causes low glucose, but paired with a sulfonylurea, it can. The same is true for newer drug classes like SGLT2 inhibitors (canagliflozin, dapagliflozin, empagliflozin) and thiazolidinediones (pioglitazone, rosiglitazone).
Non-Diabetes Drugs That Lower Blood Sugar
Several medications prescribed for completely unrelated conditions can drop your glucose. Beta-blockers used for blood pressure and heart rate (like atenolol and propranolol) are one example, and they also mask the racing heartbeat that normally alerts you to a low. Certain antibiotics, including some fluoroquinolones and the antimalarial drug quinine, have the same effect. Heart rhythm medications like quinidine and even the pain reliever indomethacin can contribute. If you’re experiencing unexplained lows, your medication list is worth reviewing.
Reactive Hypoglycemia After Meals
Some people experience low glucose not from fasting but 2 to 5 hours after eating, a pattern called reactive hypoglycemia. It’s counterintuitive: you eat, your blood sugar rises, and then it crashes below where it started.
The mechanism depends on timing. In the most common form, your pancreas releases insulin with a slight delay. By the time insulin peaks, blood sugar is already falling on its own, and the combined effect drives it too low. In roughly 50 to 70% of cases, the underlying issue is high insulin sensitivity, meaning your cells respond so aggressively to insulin that glucose gets pulled out of the bloodstream too quickly.
An earlier version of the same problem happens within the first two hours after eating. Here, food leaves the stomach unusually fast, flooding the small intestine with glucose. The gut releases signaling hormones that amplify insulin release while simultaneously suppressing glucagon, the hormone that would normally rescue a falling blood sugar. The result is a sharp spike followed by a steep drop. High-carbohydrate, low-fiber meals make both patterns worse.
Alcohol
Drinking on an empty stomach is one of the most reliable ways to trigger low glucose in someone without diabetes. The liver prioritizes breaking down alcohol over everything else, and the chemical byproducts of alcohol metabolism directly block the liver’s ability to manufacture new glucose. Specifically, processing ethanol shifts the liver’s internal chemistry in a way that shuts down the conversion of raw materials into usable glucose. It also interferes with the genetic signals that normally switch on glucose production during fasting.
This means that if you haven’t eaten in several hours and you drink heavily, your liver can’t compensate. Glycogen stores deplete, new glucose production stalls, and blood sugar falls. The risk is highest during binge drinking, overnight fasting after an evening of heavy drinking, or any time alcohol replaces a meal.
Kidney Disease
The kidneys play a larger role in blood sugar regulation than most people realize. They contribute to glucose production directly, and they help clear insulin from the bloodstream. When kidney function drops significantly (below roughly 15 to 20 mL/min of filtering capacity), both of these roles break down.
Reduced kidney mass means less glucose being released into the blood. At the same time, insulin stays in circulation longer because the kidneys aren’t clearing it efficiently. The liver’s ability to pick up the slack is also compromised by the buildup of waste products that comes with advanced kidney disease. On top of that, people with severe kidney disease often have poor appetite and muscle wasting, which means fewer raw materials available for the liver to convert into glucose. The combination makes hypoglycemia a surprisingly common complication in advanced kidney disease.
Adrenal and Hormonal Problems
Cortisol is one of the key hormones your body uses to raise blood sugar during stress, illness, or fasting. When the adrenal glands don’t produce enough cortisol, a condition called adrenal insufficiency, your counter-regulatory system is weakened. You lose the ability to mount a proper glucose defense when your body needs it most.
The risk increases substantially if growth hormone is also low, since growth hormone plays its own separate role in preventing glucose from dropping. People with pituitary disorders that affect multiple hormones are particularly vulnerable. In extreme cases, adrenal crisis, a sudden collapse of adrenal function during illness or physical stress, can cause dangerously low glucose alongside life-threatening drops in blood pressure.
Intense or Prolonged Exercise
Exercise burns glucose, which is obvious. What’s less obvious is that hypoglycemia can strike any time up to 24 hours after a workout, not just during it. The reasons are layered: exercise increases insulin sensitivity, meaning your cells continue pulling glucose from the blood more efficiently long after you’ve stopped moving. Your liver and muscle glycogen stores need time to refill, and until they do, your buffer against low glucose is thinner than normal.
This delayed effect is especially relevant for people with diabetes who use insulin. But even people without diabetes can experience it after unusually long or intense activity, particularly if they haven’t eaten enough carbohydrates to match the energy they burned.
Insulin-Producing Tumors
Insulinomas are rare tumors, usually benign, that grow in the pancreas and secrete insulin continuously regardless of blood sugar levels. They cause repeated episodes of fasting hypoglycemia that follow a classic pattern known as the Whipple triad: blood glucose drops below 50 mg/dL, neurological symptoms appear (confusion, blurred vision, difficulty concentrating), and those symptoms resolve promptly once glucose is restored. Most insulinomas are small and curable with surgery, but they can go undiagnosed for years because the symptoms mimic anxiety, fatigue, or other common conditions.
Gastric Surgery
People who have had bariatric surgery, particularly gastric bypass, are prone to a specific form of low glucose tied to how quickly food now reaches the small intestine. Without a full-sized stomach to slow digestion, nutrients flood the gut, triggering an exaggerated insulin release. This is the most common cause of hypoglycemia after bariatric surgery and typically shows up as postprandial episodes, often within the first year.
For most people, the problem improves with dietary changes: eating smaller, more frequent meals, reducing simple carbohydrates, and pairing carbs with protein and fat to slow absorption. In persistent cases, medication may be needed.
Skipping Meals and Prolonged Fasting
In a healthy person, the liver can maintain blood sugar for 24 to 48 hours of fasting by tapping glycogen stores and then switching to glucose production. But if you’re malnourished, have limited muscle mass, drink alcohol, or have any of the conditions above, that buffer shrinks. Skipping meals alone rarely causes dangerous lows in otherwise healthy adults, but it amplifies every other risk factor on this list. For someone on insulin, taking a diabetes drug, or recovering from a long workout, a missed meal can be the tipping point.