Your blood sugar drops when your body uses glucose faster than it can replace it, or when too much insulin pushes glucose out of your bloodstream at once. A reading below 70 mg/dL is considered low, and at that point most people start feeling noticeable symptoms. The causes range from something as simple as skipping a meal to underlying conditions that affect how your body regulates energy.
What a Blood Sugar Drop Feels Like
The symptoms come in two waves, depending on how far your blood sugar falls. Early on, your body releases stress hormones to try to push glucose back up. This produces sweating, a pounding heart, shakiness, anxiety, and sudden intense hunger. These warning signs are your body’s alarm system, and most people can catch a drop at this stage.
If blood sugar keeps falling, your brain starts running short on fuel. That’s when symptoms shift to confusion, difficulty concentrating, irritability, and blurred or impaired vision. In rare and severe cases, this can progress to loss of consciousness. The transition from the first set of symptoms to the second can happen quickly, which is why recognizing the early signs matters.
Too Much Insulin After Eating
One of the most common reasons blood sugar drops in people without diabetes is called reactive hypoglycemia. It typically hits two to four hours after a meal, especially one heavy in refined carbohydrates. What happens is your stomach empties quickly, causing a sharp spike in blood sugar. Your body overreacts by releasing too much insulin, and blood sugar crashes below where it started.
This pattern is driven partly by gut hormones called incretins, which amplify insulin release in response to that initial sugar spike. People with early insulin resistance are particularly prone to this cycle. In the early stages of developing type 2 diabetes, the body’s first burst of insulin after eating becomes sluggish, which causes blood sugar to spike higher than normal. The body then compensates with an exaggerated second wave of insulin, pulling blood sugar down too far. Research from the Whitehall II study found that insulin secretion starts increasing three to four years before a diabetes diagnosis as the body tries to compensate for growing insulin resistance.
If you notice symptoms a few hours after eating but have never checked your blood sugar during an episode, it’s worth knowing that a related condition called idiopathic postprandial syndrome produces the same shaky, anxious, hungry feeling with completely normal blood sugar readings. The symptoms are real, but the cause isn’t actually low glucose. The only way to tell the difference is to check your blood sugar when you feel symptomatic.
Skipping Meals and Fasting
Between meals, your liver keeps blood sugar stable by breaking down stored glycogen and converting other molecules into glucose. If you go long enough without eating, those glycogen stores run out. Your liver can still manufacture glucose from scratch, but this process has limits, especially if something else is interfering with it.
Most healthy adults can fast for extended periods without their blood sugar dropping dangerously low, because hormones like glucagon and cortisol keep the liver producing glucose. But if your liver isn’t functioning well, or if you have a hormonal deficiency that weakens this backup system, fasting can push blood sugar below safe levels. In children, insufficient growth hormone can cause the same problem.
How Alcohol Interferes
Drinking alcohol is one of the most overlooked causes of blood sugar drops. Alcohol directly impairs your liver’s ability to produce new glucose. In one study, alcohol reduced the liver’s glucose-manufacturing capacity by 45% over five hours, and the availability of the raw materials the liver uses to build glucose fell by 61%. The liver’s total glucose output dropped 12% compared to a placebo.
This effect is especially dangerous if you drink without eating, because your body is relying entirely on the liver to keep blood sugar stable. The drop can happen hours after your last drink, sometimes while you’re asleep, which makes it easy to miss. People taking diabetes medications are at even higher risk, but it can happen to anyone who drinks on an empty stomach or after intense physical activity.
Exercise and Delayed Drops
Physical activity burns through glucose, which is why blood sugar can dip during a workout. But the less obvious risk is what happens afterward. Delayed drops typically occur 8 to 12 hours after prolonged exercise. Two things drive this: your muscles and liver need to rebuild their glycogen stores, which increases glucose demand for hours, and your cells remain more sensitive to insulin well after you’ve stopped moving. That increased insulin sensitivity can persist for hours or even days.
This means a long run or intense gym session in the afternoon can set you up for a blood sugar drop in the middle of the night. Eating a balanced meal after exercise helps replenish glycogen and reduces this risk.
Medications That Lower Blood Sugar
Several medications can cause unexpected blood sugar drops, even in people who don’t have diabetes. The most common culprits include certain heart rhythm medications, some antibiotics (particularly fluoroquinolones like levofloxacin), the pain reliever indomethacin, and beta-blockers like atenolol and propranolol. Beta-blockers can also mask the early warning symptoms like a racing heart, making a drop harder to recognize.
For people with diabetes, insulin and sulfonylureas are the most frequent causes of medication-related drops. Combining diabetes drugs, such as metformin with a sulfonylurea, increases the risk further. If you’ve recently started a new medication and are noticing symptoms of low blood sugar, that’s a connection worth flagging to your prescriber.
What to Do When Your Blood Sugar Drops
The standard approach is the 15-15 rule recommended by the CDC: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process. Good sources of 15 grams of fast-acting carbs include four glucose tablets, four ounces of juice, or a tablespoon of honey.
Once your blood sugar comes back up, eat a small meal or snack with protein and complex carbohydrates to keep it stable. Simple sugar alone will raise your level quickly but won’t sustain it.
When Drops Signal Something Deeper
Doctors use a framework called the Whipple triad to determine if blood sugar drops warrant further investigation. All three criteria need to be present: a documented low blood sugar reading, symptoms consistent with low blood sugar at the time of the reading, and improvement in those symptoms once blood sugar rises. If all three are confirmed, especially if episodes are recurring, it points toward a condition that needs diagnosis rather than just a one-off event from skipping lunch.
Possible underlying causes include problems with the adrenal glands (which produce cortisol), liver disease, kidney problems, or rarely, tumors in the pancreas that overproduce insulin. These are uncommon, but recurrent unexplained drops, particularly ones that happen when you haven’t eaten, are worth investigating.