Low blood sugar (hypoglycemia) in people with diabetes is most often caused by diabetes medications, but exercise, alcohol, missed meals, and even kidney problems can also drive blood sugar below 70 mg/dL. Understanding the specific triggers helps you recognize patterns and prevent dangerous drops.
Diabetes Medications That Trigger Lows
Insulin is the most common cause of hypoglycemia in diabetes. When the dose is too high relative to what your body needs at that moment, whether because you ate less than planned, were more active, or misjudged your carbs, your blood sugar can fall quickly. Injected insulin enters your bloodstream directly and keeps working on a fixed timeline regardless of what your blood sugar is actually doing.
A class of oral medications called sulfonylureas (including glipizide, glimepiride, and glyburide) is the other major culprit. These drugs work by forcing your pancreas to release more insulin. They do this by blocking potassium channels on insulin-producing cells, which triggers calcium to flow in and stimulate insulin release. The problem is that this happens whether your blood sugar is high, normal, or already dropping. Long-acting versions like glyburide carry the highest risk because they keep stimulating insulin production for extended periods, sometimes well into the night.
Other diabetes medications, like metformin or newer drug classes such as GLP-1 receptor agonists, rarely cause hypoglycemia on their own. But combining them with insulin or sulfonylureas increases the risk significantly.
How Exercise Drops Blood Sugar
During physical activity, your muscles dramatically increase the amount of glucose they pull from your bloodstream. Normally, your body compensates by having the liver release stored glucose while insulin levels drop. But if you’ve taken insulin or a sulfonylurea, that natural safety mechanism is overridden. Your medication keeps pushing blood sugar down while your muscles are pulling it down too.
Timing matters. Exercising shortly after a meal, especially one high in carbohydrates, can cause what researchers call rebound hypoglycemia. Your body is already producing insulin in response to the meal, and the added glucose demand from exercise tips the balance. People who are naturally more insulin-sensitive tend to experience sharper drops. Their blood sugar and insulin levels fall lower during post-meal exercise compared to people with more insulin resistance.
Prolonged exercise creates a different risk: your stored fuel sources become depleted over time, and blood sugar can drop hours after you’ve stopped. This delayed effect catches many people off guard, sometimes causing lows in the middle of the night after an active afternoon.
Alcohol’s Effect on Liver Glucose
Your liver is your body’s primary backup system for maintaining blood sugar between meals. It produces new glucose through a process called gluconeogenesis. Alcohol directly shuts this process down.
When you drink, the chemical byproducts of alcohol metabolism in the liver block the conversion of raw materials into glucose. Research published in PNAS found that ethanol activates a specific protein that acts as a “switch,” turning off the genes responsible for glucose production. This means your liver can’t respond when your blood sugar starts falling. The effect is dose-dependent: binge drinking can cause life-threatening hypoglycemia by essentially disabling your liver’s glucose output entirely.
The danger is compounded for people on insulin or sulfonylureas, because the medication keeps lowering blood sugar while the liver’s rescue mechanism is offline. This risk can persist for hours after your last drink, making overnight lows especially dangerous after evening alcohol consumption.
Skipping or Delaying Meals
If you take insulin before a meal and then eat less than expected, or if your meal is delayed, the insulin peaks without enough incoming glucose to match it. The same applies to sulfonylureas, which stimulate insulin release on their own schedule regardless of whether food is present.
A related but less obvious issue is gastroparesis, a condition where nerve damage from diabetes slows the stomach’s ability to empty food into the intestines. This creates a mismatch between when your insulin peaks and when carbohydrates actually reach your bloodstream. You might take insulin at the right time for a normal meal, but if your stomach empties unpredictably, the carbs arrive late and your blood sugar drops in the gap. The CDC notes that gastroparesis makes it significantly harder to estimate how much insulin you need at mealtimes.
Kidney Problems and Insulin Buildup
Your kidneys are responsible for clearing a large portion of insulin from your body. About 60% of insulin clearance happens through filtration in the kidneys, where insulin is broken down and recycled into amino acids. When kidney function declines, a common complication of long-standing diabetes, insulin stays in your bloodstream longer than expected.
This is especially significant if you inject insulin, because injected insulin enters the bloodstream directly without passing through the liver first (where some of it would normally be broken down). The result is that doses that once worked fine may become too strong as kidney function worsens. People with advancing kidney disease often need their insulin doses reduced, sometimes substantially, to avoid repeated lows.
Overnight Lows and Morning Rebounds
Nocturnal hypoglycemia is a particular concern because you’re asleep and unable to recognize the symptoms. It commonly happens when evening insulin doses are too high or when you’ve been more active than usual during the day.
One pattern worth knowing about is the Somogyi effect. If your blood sugar drops too low overnight, your body releases a surge of adrenaline and other stress hormones to rescue you. These hormones cause the liver to dump glucose into your bloodstream, which can result in unusually high blood sugar by morning. This is different from the dawn phenomenon, where hormones like cortisol and growth hormone naturally raise blood sugar in the early morning hours without any preceding low. The distinction matters because the Somogyi effect means you need less insulin overnight, while the dawn phenomenon might mean you need more. Checking your blood sugar around 2 or 3 a.m. for a few nights can help distinguish between the two.
What to Do When Blood Sugar Drops
The standard approach recommended by the CDC is the 15-15 rule: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, and recheck your blood sugar. If it’s still below 70 mg/dL, repeat. Good sources of 15 grams of carbs include four glucose tablets, half a cup of juice, or a tablespoon of sugar dissolved in water. Keep repeating until your blood sugar returns to your target range.
Recognizing patterns is just as important as treating individual episodes. If lows keep happening at the same time of day, after the same activities, or in connection with specific meals, that’s a signal that something in your medication timing, dosing, or routine needs adjusting. Tracking when lows occur, what you ate, how active you were, and what medications you took gives you and your care team the information needed to make those changes.