Low blood sugar, or hypoglycemia, happens when blood glucose drops below 70 mg/dL. The most common cause is diabetes medication, particularly insulin and drugs that stimulate insulin production. But several other conditions and lifestyle factors can drive blood sugar too low even in people without diabetes, ranging from alcohol consumption to liver disease to rare pancreatic tumors.
Diabetes Medications
Insulin is the most straightforward culprit. Taking too much, timing a dose poorly around meals, or exercising more than expected can all tip the balance toward a blood sugar crash. This is especially common when someone skips a meal after dosing or misjudges the carbohydrate content of food.
A class of oral diabetes drugs called sulfonylureas is the other major offender. These medications work by forcing the pancreas to release preformed insulin regardless of whether blood sugar is actually elevated. They block potassium channels on insulin-producing cells, triggering a chain reaction that pushes insulin into the bloodstream. Because this process doesn’t respond to your current glucose level the way your body’s natural regulation would, these drugs can keep lowering blood sugar even after it reaches a normal range. The effect can last for hours, making repeated or prolonged low blood sugar episodes a real risk.
Alcohol
Drinking alcohol, especially on an empty stomach or after heavy exercise, is one of the most common non-diabetes causes of low blood sugar. Your liver normally keeps blood glucose stable between meals by converting stored glycogen into glucose and manufacturing new glucose from scratch (a process called gluconeogenesis). Alcohol disrupts both of these backup systems. It initially accelerates the breakdown of glycogen stores and then blocks the liver’s ability to produce new glucose once those stores run out.
The timing matters. Blood sugar may stay normal during and immediately after drinking, but drop overnight or the following morning. Research in people with type 1 diabetes found that evening alcohol consumption led to lower fasting and post-breakfast blood sugar the next day, likely due to suppressed growth hormone levels during the night. For anyone, drinking without eating enough food beforehand creates a window of vulnerability that can last well into the next day.
Reactive Hypoglycemia After Meals
Some people experience blood sugar drops within four hours after eating, a pattern called reactive or postprandial hypoglycemia. In people with diabetes, this usually traces back to medication timing. In people without diabetes, the cause is often unclear, but it tends to be connected to the type and timing of meals, particularly high-carbohydrate meals that trigger a large insulin surge followed by an overshoot.
Eating smaller, more frequent meals with a balance of protein, fat, and complex carbohydrates typically reduces these episodes. Avoiding refined sugars and processed carbohydrates helps prevent the rapid glucose spike that triggers excessive insulin release in the first place.
Bariatric Surgery
Low blood sugar after gastric bypass surgery is far more common than many patients expect. Continuous glucose monitoring studies have found that more than 50% of people who’ve undergone bariatric surgery experience hypoglycemic episodes, and mixed meal challenges trigger symptoms in up to one-third of patients.
The mechanism is straightforward: after surgery, food bypasses much of the stomach and reaches the intestine faster than normal. This rapid delivery causes a sharp, early spike in blood glucose, which triggers the gut to release large amounts of a hormone that amplifies insulin secretion. The pancreas responds with a flood of insulin that overshoots what’s needed, and blood sugar crashes. The problem is compounded by increased insulin sensitivity after weight loss and a blunted ability to release glucagon, the hormone that normally counteracts falling blood sugar. These episodes typically occur after meals rather than during fasting.
Liver and Kidney Disease
Your liver acts as a glucose reservoir. It stores excess glucose after meals as glycogen and releases it between meals to keep blood sugar stable. When liver disease, cirrhosis, or severe inflammation damages liver cells, they lose the ability to store and release glycogen effectively. The enzymes that regulate these storage and release pathways become impaired, and the liver can no longer serve as a reliable buffer against dropping blood sugar. This makes people with advanced liver disease vulnerable to hypoglycemia, particularly during fasting or overnight, with consequences that can range from confusion to loss of consciousness.
Kidney failure creates similar risks. The kidneys play a supporting role in glucose production and also clear insulin from the bloodstream. When they fail, insulin lingers longer than it should, continuing to push blood sugar down. Infections, obesity, and coexisting diabetes further compound the risk in people with either liver or kidney disease.
Insulin-Producing Tumors
Insulinomas are rare pancreatic tumors that secrete insulin independent of blood sugar levels. Because the tumor keeps pumping out insulin even when glucose is already low, people with insulinomas experience recurrent episodes of hypoglycemia, often during fasting or between meals.
Diagnosis relies on what’s known as Whipple’s triad: symptoms consistent with low blood sugar, a documented blood glucose reading below 55 mg/dL during symptoms, and improvement once carbohydrates are consumed. The gold-standard diagnostic test involves a supervised 72-hour fast in a hospital setting to see whether blood sugar drops and insulin levels remain inappropriately high. About 5% to 10% of insulinoma cases occur in people with a hereditary condition called MEN1, which predisposes them to tumors in multiple glands.
Non-Diabetes Medications
Several medications prescribed for conditions unrelated to diabetes can lower blood sugar as a side effect, though this is relatively rare. The most notable include:
- Beta-blockers like atenolol and propranolol, particularly in overdose. These drugs also mask the rapid heartbeat and trembling that normally alert you to falling blood sugar, making hypoglycemia harder to detect.
- Certain antibiotics and anti-infectives, including fluoroquinolones (like levofloxacin), quinine, and a combination antibiotic used for urinary tract and other infections (trimethoprim-sulfamethoxazole).
- Heart rhythm medications such as quinidine.
- Some pain relievers, including indomethacin.
If you’re taking any of these and experiencing symptoms like shakiness, sweating, confusion, or sudden hunger, the medication could be contributing.
Other Contributing Factors
Prolonged fasting or severely restricted calorie intake can deplete glycogen stores and exhaust the liver’s capacity to produce glucose. This is why crash diets and extended fasts occasionally lead to hypoglycemia, particularly in people who are also exercising heavily.
Certain inherited metabolic disorders interfere with the body’s ability to process or store glucose normally. These conditions are typically diagnosed in childhood but can occasionally present with unexplained low blood sugar in adults. Adrenal insufficiency and severe infections are additional, less common triggers that impair the hormonal and metabolic systems responsible for keeping blood sugar in range.
For anyone experiencing repeated episodes of low blood sugar without an obvious explanation like diabetes medication or missed meals, a proper evaluation matters. The diagnostic standard requires confirming that symptoms occur alongside a documented low glucose reading from a lab test (not just a home meter) and that those symptoms resolve once blood sugar is raised. Meeting all three of these criteria distinguishes a true hypoglycemic disorder from symptoms that merely feel like low blood sugar but have a different cause.