Low blood sugar, or hypoglycemia, happens when your blood glucose drops below 70 mg/dL. It can affect people with and without diabetes, and the causes range from medication side effects and missed meals to rare medical conditions. Understanding what triggers it helps you prevent episodes and recognize when something more serious might be going on.
Diabetes Medications Are the Most Common Cause
If you have diabetes, the most frequent reason 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. Sulfonylureas (glipizide, glimepiride, glyburide) stimulate your pancreas to release more insulin regardless of what your blood sugar is doing at that moment, which creates risk if you eat less than expected or are more active than usual. Glinides work similarly. Other drug classes don’t typically cause low blood sugar on their own but can when combined with sulfonylureas.
Three common situations turn these medications into a problem: missing or delaying a meal, getting more physical activity than usual, or accidentally taking too much. Any of these can tip the balance so your medication lowers blood sugar further than your body can compensate for.
Skipping Meals and Prolonged Fasting
Your liver stores glucose in a form called glycogen and releases it between meals to keep blood sugar stable. Those stores are limited. After roughly 24 hours of fasting, liver glycogen drops to very low levels. At that point, your body shifts to making glucose from scratch using protein and fat, a slower process that may not keep up with demand, especially if you’re also physically active.
You don’t need to fast for a full day to feel the effects. Skipping breakfast, eating a very small lunch, or going long stretches without food can lower blood sugar enough to cause shakiness, irritability, and difficulty concentrating, particularly if you’re on diabetes medication or have other risk factors.
Blood Sugar Drops After Eating
It sounds counterintuitive, but some people experience low blood sugar within four hours after a meal. This is called reactive (or postprandial) hypoglycemia. What typically happens is your body overreacts to a surge in blood sugar by releasing too much insulin, which then drives glucose down too far.
In people without diabetes, the exact cause often isn’t clear. Known triggers include alcohol consumed with a meal, inherited metabolic conditions, and certain types of tumors. People who’ve had gastric bypass or other bariatric surgery are especially prone to it because food moves through the stomach much faster, causing rapid glucose spikes followed by steep drops. If you notice symptoms like lightheadedness, sweating, or brain fog a couple of hours after eating, particularly after high-carbohydrate meals, reactive hypoglycemia is worth investigating.
Alcohol and Your Liver
Alcohol is one of the more underappreciated causes of low blood sugar. When you drink, your liver prioritizes breaking down alcohol over its other jobs, including releasing stored glucose. Research published in the American Journal of Physiology found that alcohol reduced the liver’s ability to produce new glucose by 60 to 75 percent in fasting individuals. That’s a dramatic drop in your body’s main backup system for keeping blood sugar stable.
The risk is highest when you drink on an empty stomach or after skipping meals, because your liver glycogen stores are already partially depleted. Drinking in the evening can also lead to low blood sugar overnight or the next morning, when you may not notice the warning signs because you’re asleep. For people on insulin or sulfonylureas, alcohol adds a second layer of risk on top of the medication’s glucose-lowering effect.
Exercise and Delayed Drops
Physical activity burns glucose. Your muscles pull it from the bloodstream for energy, and prolonged or intense exercise can deplete the glycogen stored in your liver and muscles. For people with diabetes, this is a well-known trigger. But the timing can be surprising: blood sugar doesn’t just drop during a workout. It can fall hours later.
After exercise, your body remains more sensitive to insulin, and your muscles continue absorbing glucose to replenish their depleted stores. This means a low blood sugar episode can occur several hours after you’ve finished exercising, sometimes up to 24 hours later. This delayed effect catches many people off guard, especially after an unusually long run, a tough gym session, or a day of physical labor they aren’t accustomed to. Eating a balanced snack after exercise and monitoring how you feel in the hours that follow can help you stay ahead of it.
Medical Conditions That Cause Hypoglycemia
In people without diabetes, persistent or unexplained low blood sugar sometimes points to an underlying condition. The most well-known is an insulinoma, a small tumor in the pancreas that produces excess insulin. About 90 to 95 percent of insulinomas are benign, and they’re diagnosed using a set of criteria known as the Whipple triad: you have symptoms of low blood sugar, a blood test confirms glucose is actually low at the time, and the symptoms go away once glucose is restored. The hallmark is inappropriately high insulin levels when blood sugar is low, because a healthy pancreas would have stopped releasing insulin at that point.
Other conditions that can cause hypoglycemia include adrenal insufficiency (where your body doesn’t produce enough of the hormones that raise blood sugar in response to a drop), severe liver disease (since the liver is central to glucose production), and critical illnesses like sepsis or kidney failure. These are uncommon causes, but they’re important to rule out when someone without diabetes has repeated episodes of low blood sugar without an obvious trigger.
What Low Blood Sugar Feels Like
Early symptoms are your body’s alarm system. You may notice shakiness, sweating, a fast heartbeat, hunger, irritability, or anxiety. These happen because your body releases stress hormones to try to push blood sugar back up. As glucose drops further, the brain starts to feel the shortage: confusion, difficulty speaking, blurred vision, and trouble concentrating set in.
Severe hypoglycemia, defined as blood sugar below 54 mg/dL, can cause seizures or loss of consciousness. At that point, you need someone else’s help to recover, whether that’s a glucagon injection or emergency medical care. If someone is unconscious, don’t try to put food or drink in their mouth.
When Warning Signs Disappear
One of the more dangerous complications is called hypoglycemia unawareness. When low blood sugar happens repeatedly, your body can stop producing the normal warning signals. The stress hormones that cause shakiness and sweating become blunted, so you feel fine until your blood sugar is dangerously low. This condition, sometimes called hypoglycemia-associated autonomic failure, substantially increases the risk of severe episodes because you lose the early window to treat the drop. It’s most common in people with long-standing type 1 diabetes or anyone who has frequent hypoglycemic episodes.
Preventing Low Blood Sugar
Prevention depends on the cause. If you take insulin or medications that stimulate insulin release, eating consistent meals and snacks is the simplest protection. Pairing carbohydrates with protein or fat slows digestion and prevents the rapid glucose swings that lead to lows. Before and after exercise, a small carbohydrate-containing snack can offset the extra glucose your muscles are burning.
If you drink alcohol, eating beforehand and keeping portions moderate reduces your liver’s vulnerability. Checking blood sugar before bed after a night of drinking is a practical habit for anyone on glucose-lowering medication. For people experiencing reactive hypoglycemia, smaller and more frequent meals with less refined carbohydrate tend to smooth out the post-meal insulin response that drives glucose down.
Keeping fast-acting glucose within reach, such as glucose tablets, juice, or regular soda, lets you treat a mild episode before it becomes severe. The standard recommendation is 15 grams of fast-acting carbohydrate, then waiting 15 minutes and rechecking. For people on insulin, carrying a glucagon kit provides a safety net for situations where eating isn’t possible.