Blood sugar drops below normal when your body uses glucose faster than it can replace it, or when something interferes with the systems that keep glucose steady. For most people with diabetes, a reading below 70 mg/dL counts as low blood sugar (hypoglycemia). The causes range from everyday triggers like skipping meals and exercising hard to medications, alcohol, and less common medical conditions.
Diabetes Medications
Insulin and a class of oral medications called sulfonylureas are the most frequent culprits behind low blood sugar in people with diabetes. Sulfonylureas work by stimulating your pancreas to push more insulin into your bloodstream. If you take too much, take your dose without eating, or accidentally double up after missing a dose, the extra insulin pulls too much glucose out of your blood. The same logic applies to injectable insulin: too large a dose, poor timing relative to meals, or miscalculating carbohydrates can all send levels plummeting.
Certain other medications amplify the effect. Combining sulfonylureas with common drugs like NSAIDs (ibuprofen, naproxen), some antibiotics, antifungal medications, or blood thinners can increase your risk of a dangerous drop. If you take any combination of blood sugar-lowering medications, the margin for error gets smaller.
Skipping or Delaying Meals
Your body pulls glucose from the food you eat. When you skip a meal, eat much less than usual, or go longer than expected between meals, your blood sugar can fall simply because there’s not enough incoming fuel. This is especially risky if you’re also taking insulin or sulfonylureas, because those medications keep working whether you’ve eaten or not. Even people without diabetes can experience symptoms like shakiness or lightheadedness from going too long without food, though their bodies will typically correct the imbalance on their own.
Exercise and the Delayed Drop
Physical activity pulls glucose into your muscles for energy, which naturally lowers blood sugar. The surprise for many people is that this effect doesn’t stop when the workout ends. After exercise, your muscles continue absorbing glucose to replenish their energy stores, and your cells stay more sensitive to insulin for hours. This delayed drop can happen several hours after you finish exercising, catching people off guard well into the evening or even overnight after an afternoon workout.
The risk is highest with prolonged or intense exercise, especially if you haven’t adjusted your food intake or medication timing. Even a long walk or yard work session can trigger it if conditions line up.
Alcohol
Alcohol blocks your liver’s ability to release stored glucose into your bloodstream. Normally, when blood sugar starts to dip between meals or overnight, your liver converts stored glycogen into glucose and sends it out to keep levels stable. Alcohol disrupts this process at a chemical level, preventing the liver from manufacturing new glucose. The result is that your blood sugar can drop and stay low for hours.
This effect is strongest when you drink on an empty stomach or drink heavily, but even moderate amounts can cause problems, particularly if you’re also taking diabetes medication. The risk can persist for several hours after your last drink, since your liver stays occupied processing the alcohol.
Reactive Hypoglycemia After Meals
Some people experience a blood sugar drop one to four hours after eating, even without diabetes. This is called reactive (or postprandial) hypoglycemia. What typically happens is that a meal high in refined carbohydrates or sugar triggers a large spike in blood sugar, which prompts an oversized insulin response. The excess insulin then drives blood sugar below where it started.
The exact cause isn’t always clear, but it’s more common in people who have had gastric bypass or other bariatric surgery. After these procedures, food moves into the small intestine much faster than normal, causing a rapid sugar surge followed by an exaggerated insulin release. This pattern, sometimes called dumping syndrome, tends to hit one to three hours after eating a starchy or sugary meal. Alcohol and certain inherited metabolic conditions can also trigger reactive episodes.
Kidney and Liver Disease
Your liver and kidneys both play critical roles in keeping blood sugar stable. The liver stores glucose and releases it when needed. The kidneys help clear insulin and other hormones from the blood. When either organ is significantly damaged, the system breaks down.
Advanced kidney disease disrupts glucose and insulin metabolism in multiple ways. Among the most important: the kidneys normally break down and remove insulin from the body, so when they stop working efficiently, insulin lingers in the bloodstream longer than it should, pulling blood sugar lower. This is compounded if someone is also taking insulin or other diabetes medications, because the kidneys can no longer clear those drugs at the expected rate. Liver disease, particularly cirrhosis, reduces the organ’s ability to store and release glucose on demand, leaving blood sugar vulnerable to drops during fasting or overnight.
Adrenal Insufficiency
Your adrenal glands produce cortisol, a hormone that helps your body convert food into energy and signals the liver to release glucose when levels run low. In Addison’s disease (primary adrenal insufficiency) or secondary adrenal insufficiency caused by pituitary problems, cortisol production falls short. Without enough cortisol, your body loses one of its key mechanisms for propping up blood sugar between meals and during stress. People with secondary adrenal insufficiency are particularly prone to low blood sugar episodes. During an adrenal crisis, blood sugar can drop dangerously low alongside a sharp fall in blood pressure.
Insulinoma
Rarely, a small tumor in the pancreas called an insulinoma produces excess insulin regardless of what your blood sugar is doing. These tumors are uncommon, but they cause repeated, unexplained episodes of low blood sugar that can be confusing to diagnose. The hallmark pattern, known as Whipple’s triad, involves three things happening together: symptoms of low blood sugar, a confirmed reading below 55 mg/dL, and improvement after eating carbohydrates. The good news is that 85% to 90% of insulinomas are benign and don’t spread beyond the pancreas. About 5% to 10% of cases are linked to a genetic condition called MEN1.
What a Blood Sugar Drop Feels Like
Mild drops often start with shakiness, sweating, a fast heartbeat, and sudden hunger. You might feel anxious, irritable, or lightheaded. As blood sugar falls further, symptoms shift toward confusion, difficulty concentrating, blurred vision, slurred speech, and poor coordination. Severe hypoglycemia can cause seizures or loss of consciousness, though this is far less common and usually involves diabetes medication or an underlying condition.
Symptoms can vary from person to person, and some people who have frequent low episodes gradually lose the ability to feel early warning signs, a phenomenon sometimes called hypoglycemia unawareness.
How to Treat a Drop Quickly
The standard approach is the 15/15 rule: eat 15 grams of fast-acting carbohydrates, then wait 15 minutes and recheck. Foods that deliver roughly 15 grams include three glucose tablets, half a cup (4 ounces) of juice or regular soda, six or seven hard candies, or one tablespoon of sugar. If you still don’t feel better after 15 minutes, repeat with another 15 grams. Once blood sugar returns to normal, eating a small meal or snack with protein and complex carbohydrates helps prevent another dip.