Blood sugar drops when the body uses glucose faster than it can replace it, or when too much insulin pushes glucose out of the bloodstream and into cells. For most people, the body’s hormonal safety net prevents this from happening. In people with diabetes who take insulin or certain oral medications, though, low blood sugar is the single most common drug-related complication. The causes range from everyday triggers like skipped meals and exercise to rare conditions like insulin-producing tumors, and understanding the spectrum matters because the right response depends entirely on the underlying reason.
How Your Body Normally Prevents Low Blood Sugar
Your body runs on glucose the way a car runs on fuel, and it has an elaborate system for keeping the tank from running empty. When blood sugar starts to fall, the pancreas dials back insulin and ramps up a hormone called glucagon, which signals the liver to break down stored glycogen into glucose and release it. If that is not enough, stress hormones like adrenaline and cortisol kick in to raise blood sugar further. These layered defenses make true hypoglycemia rare in healthy people who do not take blood-sugar-lowering medications.1PubMed Central. Glucose counterregulatory responses to hypoglycemia
Problems arise when one or more layers of that safety net get disrupted. Medications can override the system by forcing insulin levels too high. Alcohol can block the liver’s ability to manufacture new glucose. Tumors can flood the body with insulin or insulin-like substances. And certain hormonal deficiencies can eliminate the backup responses that are supposed to catch you when insulin overshoots. Each of these represents a fundamentally different mechanism, and they produce low blood sugar in different contexts.
Recognizing the Symptoms
When blood sugar falls, the body sends two distinct categories of warning signals. The first wave comes from your autonomic nervous system reacting to the drop: shakiness, a pounding heart, anxiety, sweating, hunger, and tingling sensations.2PubMed. Mechanism of awareness of hypoglycemia. Perception of neurogenic (predominantly cholinergic) rather than neuroglycopenic symptoms These are essentially alarm bells, and most people learn to recognize them.
The second wave comes from the brain itself running short on fuel: confusion, weakness, fatigue, a sensation of warmth, difficulty thinking clearly, and in severe cases, seizures or loss of consciousness.3PubMed. Symptoms of hypoglycemia, thresholds for their occurrence, and hypoglycemia unawareness These brain-based symptoms are more dangerous because by the time they appear, your ability to help yourself is already compromised. Someone who is confused may not think to eat something, and someone who has lost consciousness obviously cannot.
Diabetes Medications, the Most Common Culprit
The overwhelming majority of hypoglycemic episodes happen in people taking insulin or a class of oral drugs called sulfonylureas. These medications lower blood sugar by design, and when dosing outpaces what the body needs, or when a meal is delayed or smaller than expected, blood sugar overshoots downward. Among older adults with diabetes who experienced severe hypoglycemia, roughly 57 percent of episodes occurred in those on insulin alone, about 30 percent in those on a sulfonylurea alone, and the remainder in people taking both.4PubMed Central. Deintensification of Treatment With Sulfonylurea and Insulin After Severe Hypoglycemia Among Older Adults With Diabetes
The reason these two drug classes dominate the statistics is that they work regardless of what your blood sugar is doing. Insulin injected under the skin keeps acting whether or not you eat. Sulfonylureas stimulate the pancreas to release insulin around the clock, not just when glucose is elevated. Newer diabetes medications like GLP-1 receptor agonists and SGLT2 inhibitors are much less likely to cause hypoglycemia on their own because their glucose-lowering effect depends on blood sugar being elevated in the first place. If you are on insulin or a sulfonylurea and experience frequent lows, that is a conversation worth having with your doctor about whether the regimen can be adjusted.
Overdose of either insulin or sulfonylureas, whether accidental or intentional, carries particular risk because the resulting hypoglycemia can be prolonged and severe.5PubMed Central. Treatment of sulfonylurea and insulin overdose Sulfonylurea overdoses are especially tricky because the drugs have long half-lives, meaning blood sugar can crash again hours after an initial recovery, sometimes requiring extended hospital monitoring.
Exercise and Blood Sugar
Physical activity pulls glucose out of the bloodstream and into working muscles, which is normally a good thing. In people who manage diabetes with insulin or sulfonylureas, though, exercise adds a second force pulling blood sugar down on top of medication that is already doing the same thing. The risk does not end when the workout does. Muscles continue replenishing their glycogen stores for hours afterward, which means blood sugar can drop well after you have stopped exercising.6PubMed Central. Exercise-related hypoglycemia in diabetes mellitus
What makes this trickier is that repeated episodes of exercise-related hypoglycemia can dull the body’s ability to defend against future lows. Antecedent exercise blunts the hormonal counter-regulatory responses that normally kick in when blood sugar drops, creating a feedback loop where each episode makes the next one harder to detect and prevent.6PubMed Central. Exercise-related hypoglycemia in diabetes mellitus For people with diabetes who exercise regularly, this usually means adjusting medication doses on workout days, having fast-acting carbohydrates on hand, and sometimes checking blood sugar mid-workout.
In people without diabetes, exercise very rarely causes true hypoglycemia. You might feel shaky or lightheaded after a long run on an empty stomach, but your liver and hormonal systems almost always compensate before blood sugar falls to a clinically dangerous level.
Alcohol and Fasting
Alcohol is one of the few substances that can cause genuine hypoglycemia even in people who do not have diabetes, though the circumstances have to be right. When your liver is busy processing alcohol, it diverts resources away from manufacturing new glucose, a process called gluconeogenesis. In overnight-fasted men, alcohol reduced gluconeogenesis by about 45 percent compared to a placebo.7PubMed. The inhibition of gluconeogenesis following alcohol in humans The mechanism is well understood at a biochemical level: the enzyme that breaks down alcohol shifts the liver’s chemical balance in a way that starves the glucose-making pathway of what it needs to function.8PubMed Central. Inhibition of hepatic gluconeogenesis by ethanol
The risk is highest when someone drinks on an empty stomach or after not eating for an extended period, because under those conditions the liver’s glycogen reserves are already low and gluconeogenesis is the primary thing keeping blood sugar up. Binge drinking without food is a classic setup. In people with diabetes on insulin, alcohol compounds the medication risk and can cause delayed hypoglycemia hours later, sometimes in the middle of the night. The practical advice is straightforward: if you drink, eat something alongside it, and if you take insulin, monitor your blood sugar more closely than usual.
When Warning Signs Disappear
One of the more unsettling complications of recurrent hypoglycemia is that the body can stop sounding the alarm. This condition, called hypoglycemia unawareness, develops when the brain recalibrates its threshold for triggering warning symptoms. After repeated episodes, the autonomic nervous system stops responding at the blood sugar levels where it used to kick in. The result is that blood sugar can plunge to dangerously low levels without the shakiness, sweating, and racing heart that would normally alert you to eat something.9PubMed Central. Hypoglycemia Unawareness-A Review on Pathophysiology and Clinical Implications
The causes are multifactorial: chronic exposure to low blood sugar, recurrent severe episodes, and progressive failure of counter-regulatory hormones all contribute.10PubMed Central. Mechanisms of hypoglycemia unawareness and implications in diabetic patients This creates a vicious cycle. Without warning symptoms, episodes go unrecognized and untreated, which causes more recurrent hypoglycemia, which further blunts the warning system. People with type 1 diabetes and long-standing type 2 diabetes on intensive insulin therapy are most affected. Continuous glucose monitors have become especially valuable for these individuals, since the device can alarm when blood sugar drops even when the body will not.
The encouraging news is that hypoglycemia unawareness is at least partially reversible. Strictly avoiding hypoglycemia for several weeks can restore some of the counter-regulatory response and bring warning symptoms back, though the recovery is often incomplete.
Hypoglycemia After Bariatric Surgery
A cause that has become more visible as weight-loss surgery has grown more common is post-bariatric hypoglycemia. After procedures like gastric bypass, the rerouted digestive tract delivers nutrients to the small intestine faster than normal, which can trigger an exaggerated insulin surge after meals. Blood sugar spikes briefly, then crashes as the excess insulin takes effect.11PubMed Central. Postprandial hypoglycemia as a complication of bariatric and metabolic surgery: a comprehensive review of literature
This typically does not show up immediately after surgery. It tends to develop months to years later, and it can catch people off guard because they may never have had blood sugar problems before. The episodes usually happen one to three hours after eating, particularly after meals heavy in refined carbohydrates. Dietary modifications, specifically eating smaller meals with more protein and fewer simple sugars, are the first-line approach. For severe cases, medications that slow gastric emptying or reduce insulin secretion are sometimes used.
Insulin-Producing Tumors
Insulinomas are small tumors of the pancreas that secrete insulin independently of blood sugar levels. They are rare, occurring in roughly one to four people per million, but they are the most common cause of hypoglycemia driven by the body’s own excess insulin production.12PubMed Central. Diagnosis and management of insulinoma The hallmark is fasting hypoglycemia: blood sugar drops after going without food, rather than in the hours after a meal. Most insulinomas are benign and can be cured with surgical removal.
Even rarer are non-islet cell tumors, usually large mesenchymal or epithelial tumors that secrete a substance called “big” IGF-2, which mimics insulin’s effects. This drives glucose into cells and simultaneously shuts down the liver’s glucose production, causing profound hypoglycemia.13Endocrine Practice. Non-Islet Cell Tumor Hypoglycemia: A Rare but Important Paraneoplastic Syndrome – Case Reports and Review These tumors tend to be large enough to find on imaging, but the connection between the tumor and the blood sugar episodes is not always made immediately, since hypoglycemia is not usually the first thing clinicians think of when evaluating a large abdominal mass.
Autoimmune Hypoglycemia
Insulin autoimmune syndrome, also known as Hirata disease, is a rare condition where the body produces antibodies that bind to its own insulin. The mechanism is counterintuitive: after a meal, these antibodies grab onto insulin and prevent it from working, so blood sugar initially rises. Then, unpredictably, the antibodies release their cargo of insulin all at once, flooding the bloodstream and causing a delayed crash.14PubMed Central. Insulin Autoimmune Syndrome (Hirata Disease): A Comprehensive Review Fifty Years After Its First Description
Hirata disease is most commonly described in people of East Asian descent and in individuals exposed to certain sulfur-containing medications.15PubMed Central. Insulin autoimmune hypoglycemia unmasking monoclonal gammopathy in type 2 diabetes But cases have been reported worldwide, and the condition can be confused with an insulinoma because both produce high insulin levels alongside low blood sugar. The distinguishing feature is the extremely high titer of insulin autoantibodies in the blood. Many cases resolve on their own or after the offending medication is stopped, though some require immunosuppressive treatment.
Hormonal Deficiencies and Organ Failure
Several endocrine disorders can leave the body unable to defend against falling blood sugar. Adrenal insufficiency, where the adrenal glands do not produce enough cortisol, is among the most clinically relevant. Cortisol plays a key role in glucose counter-regulation, particularly during periods of physical stress. Without adequate cortisol, the backup systems that are supposed to raise blood sugar when it drops simply do not fire properly. Newborns and young children with adrenal insufficiency are especially vulnerable, though older children and adults remain at risk as well.16PubMed Central. Hypoglycaemia in adrenal insufficiency Growth hormone deficiency and severe hypothyroidism can produce similar vulnerabilities, though less dramatically.
Severe illness involving the liver or kidneys can also cause hypoglycemia. The liver is the primary organ responsible for both storing and manufacturing glucose, so advanced liver disease directly undermines blood sugar maintenance. Kidney failure contributes through multiple mechanisms: the kidneys themselves perform some gluconeogenesis, they clear insulin from the bloodstream, and kidney failure often coincides with poor nutritional intake. Triggers in people with kidney failure include alcohol, sepsis, malnutrition, and concurrent liver disease.17PubMed. Hypoglycemia associated with renal failure Sepsis on its own can cause hypoglycemia in critically ill patients, even without preexisting kidney or liver problems, because the massive inflammatory response alters glucose metabolism throughout the body.
Hypoglycemia in Infants and Children
Newborns and young children occupy a distinct category because their smaller glycogen reserves and higher brain-to-body glucose demands make them more susceptible to low blood sugar. Some are born with genetic conditions that cause the pancreas to release insulin inappropriately. Congenital hyperinsulinism, the most common genetic cause of persistent hypoglycemia in infancy, involves defects in the molecular machinery that controls insulin secretion from pancreatic beta cells. It can cause severe hypoglycemia within hours of birth.18Voprosy detskoj dietologii. Differential diagnosis of hypoglycemia caused by congenital hyperinsulinism
The condition comes in different forms. Some involve a single focal lesion in the pancreas that can be surgically removed, while others affect the entire organ and may require near-total pancreatectomy if medications fail. Genetic testing has become central to guiding treatment, because the specific gene mutation often predicts whether the disease will respond to drug therapy or require surgery. Beyond congenital hyperinsulinism, children can also develop hypoglycemia from metabolic storage disorders, hormone deficiencies, and ketotic hypoglycemia, a common but poorly understood condition in toddlers where blood sugar drops after a period of fasting or illness.
Unusual Dietary and Toxicological Causes
Certain foods and plant compounds can directly cause hypoglycemia through their chemical effects on metabolism. The most well-documented example is the unripe ackee fruit, a staple in Caribbean cuisine. Unripe ackee contains hypoglycin A, a toxin that shuts down the liver’s ability to burn fatty acids for energy and to make new glucose. With both fuel sources compromised, blood sugar falls once glycogen stores are exhausted.19International Journal of Diabetes and Clinical Research. New Development of Hypoglycemia in a Previously Poorly-Controlled Type 2 Diabetic: Ackee Fruit-Induced Hypoglycemia Jamaican vomiting sickness, the acute illness caused by ackee poisoning, has been recognized for over a century, and proper preparation of the fruit (allowing it to ripen fully and open naturally on the tree) eliminates the toxin.
Other medications besides diabetes drugs can occasionally cause hypoglycemia as a side effect. Quinolone antibiotics, pentamidine (used for certain parasitic infections), and some beta-blockers have been reported to lower blood sugar, though far less predictably than insulin or sulfonylureas. Beta-blockers deserve special mention because they can also mask the adrenergic warning symptoms of hypoglycemia, like rapid heart rate and tremor, making lows harder to detect even when they occur for other reasons.
When Lab Results Lie
Not every low blood sugar reading on a lab report reflects what is actually happening inside the body. A phenomenon called pseudohypoglycemia or artifactual hypoglycemia occurs when glucose is consumed by blood cells in the test tube between the time the sample is drawn and when it is analyzed. This is particularly common in people with very high white blood cell counts, such as those with leukemia. The white cells metabolize glucose in the collection tube, producing a falsely low reading that has nothing to do with the patient’s real blood sugar.20Journal of the Endocrine Society. 8094 When Low Blood Sugar Isn’t Just A Lab Glitch
The danger is twofold. A clinician might chase a low blood sugar that does not actually exist, subjecting the patient to unnecessary workups. Or, as documented in at least one case report, the assumption that low readings are all artifactual might obscure a real problem, such as an insulinoma hiding behind what everyone assumed was a lab artifact. The fix is simple in theory: processing the blood sample quickly or using a tube with a glycolysis inhibitor prevents in-tube glucose consumption. In practice, though, the possibility of pseudohypoglycemia gets overlooked when leukemia is not on anyone’s radar, and it gets over-diagnosed when it is.
Reactive Hypoglycemia Without Any Clear Diagnosis
Many people without diabetes, and without any of the conditions described above, report symptoms that feel like low blood sugar one to four hours after eating: shakiness, lightheadedness, sweating, irritability. This is sometimes called reactive or postprandial hypoglycemia, and it occupies a genuinely murky area of medicine. Some of these individuals, when tested with a glucose tolerance test, do show blood sugar dipping below normal ranges after a glucose load. Others show symptoms at blood sugar levels that are technically within normal limits, suggesting their bodies are reacting to the speed of the drop rather than the absolute number.
The condition is real but frustratingly undercharacterized. There is no consensus on a single mechanism: in some people it appears to be an exaggerated insulin response to carbohydrates, while in others it may reflect heightened sensitivity to normal counter-regulatory hormone surges. Practical management tends to be the same regardless: eat smaller, more frequent meals, favor protein and fiber over refined carbohydrates, and avoid large sugar loads on an empty stomach. If the symptoms are severe or recurrent, it is worth getting tested to rule out the rarer causes, because the early symptoms of an insulinoma or Hirata disease can look exactly like garden-variety reactive hypoglycemia.