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. Blood sugar below 70 mg/dL is considered low, and below 54 mg/dL is clinically significant. This can happen to anyone, not just people with diabetes, and the causes range from something as simple as skipping a meal to hormonal imbalances that need medical attention.
How Your Body Normally Prevents a Drop
Your body has a sophisticated system for keeping blood sugar stable. When glucose starts falling, the pancreas cuts back on insulin and ramps up glucagon, a hormone that tells the liver to release stored glucose. At the same time, your adrenal glands release stress hormones like cortisol and adrenaline, which push even more glucose into the bloodstream, slow down glucose use in non-essential tissues, and break down fat as a backup fuel for the brain.
When any part of this system misfires, whether it’s too much insulin, a sluggish liver, or insufficient stress hormones, blood sugar drops below where it should be.
The Post-Meal Blood Sugar Crash
One of the most common reasons for blood sugar drops is reactive hypoglycemia, where your blood sugar falls within four hours after eating. This typically happens when your body overreacts to a meal by releasing more insulin than it needs. The insulin does its job too well, pulling so much glucose out of your blood that levels dip below normal.
Meals high in refined carbohydrates and sugar tend to trigger this pattern. Your blood sugar spikes quickly, the pancreas floods the system with insulin to compensate, and the resulting overcorrection leaves you shaky, foggy, and hungry a couple of hours later. People who’ve had bariatric surgery or other upper gastrointestinal procedures are especially prone to this because food moves into the small intestine faster, triggering a larger insulin surge.
If this sounds familiar, eating smaller meals with more protein, fiber, and fat (which slow glucose absorption) can blunt the spike and prevent the crash that follows.
Alcohol and Blood Sugar
Alcohol is one of the most overlooked causes of low blood sugar. When your liver breaks down alcohol, the chemical process shifts the liver’s internal chemistry in a way that blocks gluconeogenesis, your liver’s ability to manufacture new glucose. Essentially, your liver gets so busy processing alcohol that it can’t do its other critical job of keeping your blood sugar stable.
This effect is strongest when you drink on an empty stomach or after prolonged fasting, because your glycogen stores (the liver’s quick-access glucose reserve) are already low. The drop can happen hours after drinking, which is why some people wake up with hypoglycemia symptoms the morning after heavy alcohol consumption.
Exercise-Related Drops
Physical activity dramatically increases how fast your muscles pull glucose from the blood. Normally, the liver ramps up glucose production to keep pace. But if production can’t match the rate of uptake, blood sugar falls.
What makes this tricky is timing. Research shows that exercising after a meal can lead to transient hypoglycemia even in people with normal metabolic function. People who are more insulin-sensitive appear to experience lower glucose and insulin levels during post-meal exercise, meaning the fitter you are, the more efficiently your muscles absorb glucose, and the more likely you are to dip low during or after a hard workout. Eating a balanced snack before intense exercise and refueling afterward helps prevent this.
Medications That Lower Blood Sugar
Several medications prescribed for conditions unrelated to diabetes can cause blood sugar drops as a side effect. These include certain beta-blockers used for blood pressure and heart rate, some heart rhythm medications, certain antibiotics (particularly fluoroquinolones like levofloxacin), and some anti-inflammatory pain relievers. Beta-blockers are particularly sneaky because they can also mask the early warning signs of low blood sugar, like a racing heart and trembling, making it harder to recognize the problem.
If you’ve recently started a new medication and are noticing symptoms of low blood sugar, that connection is worth exploring with your prescriber.
Hormonal Causes
Cortisol plays a direct role in maintaining blood sugar between meals. It tells the liver to produce glucose and makes tissues less responsive to insulin, keeping blood sugar from dropping too low. When the adrenal glands don’t produce enough cortisol, whether from adrenal insufficiency or a problem with the pituitary gland that controls them, blood sugar can fall to dangerously low levels. In some cases, recurrent unexplained hypoglycemia is the first sign of an adrenal or pituitary problem.
Growth hormone works similarly, and a deficiency can also impair the body’s ability to maintain glucose levels during fasting. These hormonal causes are less common but important to consider when blood sugar drops keep happening without an obvious trigger.
More Serious Underlying Causes
In rare cases, recurring blood sugar drops point to something that needs medical workup. An insulinoma, a small tumor in the pancreas, can continuously produce excess insulin regardless of what you eat. Liver disease, kidney failure, and severe infections can all impair the body’s ability to regulate glucose. Certain non-pancreatic tumors can produce substances that mimic insulin’s effects, driving blood sugar down.
Doctors confirm a true hypoglycemic disorder using three criteria known as Whipple’s triad: you have symptoms consistent with low blood sugar, a lab test (not a home glucose meter) confirms low glucose while you’re symptomatic, and your symptoms resolve once blood sugar is raised. Meeting all three distinguishes a real disorder from symptoms that mimic hypoglycemia but have other explanations.
Recognizing the Symptoms
Low blood sugar produces two waves of symptoms. The first wave comes from your body’s stress response: sweating, a pounding or racing heart, trembling, anxiety, and sudden intense hunger. These adrenaline-driven symptoms serve as an early warning system.
If blood sugar continues to fall, a second set of symptoms appears as the brain runs short on fuel: confusion, difficulty concentrating, irritability, slurred speech, and in severe cases, loss of consciousness. The early stress symptoms don’t always show up, especially in people who experience frequent lows or take beta-blockers, so it’s possible to go straight to confusion without the usual warning signs.
What To Do When It Happens
The standard approach for a blood sugar drop is the 15-15 rule recommended by the CDC: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. Fifteen grams looks like four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. If your level is still low after 15 minutes, repeat the process.
Once your blood sugar stabilizes, follow up with a small meal or snack that includes protein and complex carbohydrates to prevent another drop. If you lose consciousness or can’t swallow safely, that’s a medical emergency requiring immediate help from someone else.
For people who experience drops regularly, keeping a log of when they happen, what you ate, how much you exercised, and what medications you took can reveal patterns. That information is far more useful to a doctor than a single reading, and it often points directly to the cause.