Low blood sugar, or hypoglycemia, happens when your blood glucose drops below 70 mg/dL. At that level, your body doesn’t have enough fuel to function normally, and you start feeling it. The reasons range from something as simple as skipping a meal to hormonal imbalances, medication side effects, or how your body processes food after eating. Understanding what’s behind your episodes is the first step toward preventing them.
What Counts as Low Blood Sugar
Blood sugar below 70 mg/dL is considered low and can cause noticeable symptoms. Below 54 mg/dL is a medical emergency that requires immediate action. These thresholds apply whether or not you have diabetes, though the causes differ significantly between the two groups.
Doctors confirm a true hypoglycemic disorder using three criteria: you have symptoms consistent with low blood sugar, a lab test shows your glucose is actually low at that moment, and your symptoms go away once your blood sugar comes back up. This matters because many symptoms of hypoglycemia overlap with anxiety, dehydration, and other conditions. If you’re getting frequent episodes, a proper lab measurement during symptoms (not just a home glucose meter reading) helps confirm what’s going on.
The Most Common Causes
Reactive Hypoglycemia After Meals
If your blood sugar crashes within four hours of eating, that’s called reactive (or postprandial) hypoglycemia. Your body releases too much insulin in response to a meal, which drives blood sugar down past where it should be. This is more likely after meals heavy in refined carbohydrates or sugar, which cause a sharp spike followed by an overcorrection.
In people without diabetes, the exact mechanism often isn’t clear. But the pattern is consistent: what you eat and when you eat it are the primary triggers. Eating smaller, more balanced meals with protein, fat, and fiber alongside carbohydrates slows digestion and prevents the rapid glucose spike that leads to the crash.
Skipping Meals or Not Eating Enough
Your liver stores glucose and releases it between meals to keep your blood sugar stable. But those stores are limited. If you skip meals, fast for extended periods, or eat too little, your liver runs low on stored glucose and can’t keep up. This is one of the simplest and most common explanations, especially if your episodes happen when you’ve gone a long time without food.
Alcohol
Drinking alcohol, particularly on an empty stomach, can cause a significant drop in blood sugar. Alcohol blocks your liver’s ability to produce new glucose from scratch, a process called gluconeogenesis. Research has shown that alcohol reduces this glucose production by roughly 45% in the five hours after drinking. Your liver’s overall glucose output drops, and the raw materials it needs to make glucose become about 61% less available.
This effect is most dangerous when your liver’s stored glucose is already low, like after exercise, fasting, or eating poorly. The combination of alcohol and an empty stomach is a reliable recipe for hypoglycemia.
Medications
Several medications can lower blood sugar as a side effect, even in people who don’t have diabetes. Beta blockers, commonly prescribed for high blood pressure, are one well-known example. They can also mask the early warning signs of low blood sugar (like a racing heart), making it harder to catch a drop before it gets serious. If you take diabetes medications, taking too much insulin is one of the most common causes of hypoglycemia.
Hormonal Problems
Cortisol, produced by your adrenal glands, plays a direct role in how your body converts food into energy and maintains blood sugar between meals. When your adrenal glands don’t produce enough cortisol (a condition called adrenal insufficiency), your body loses one of its key tools for keeping glucose stable. People with secondary adrenal insufficiency are especially prone to low blood sugar episodes. Thyroid disorders and pituitary gland problems can also disrupt the hormonal balance that regulates glucose.
Previous Stomach Surgery
If you’ve had gastric bypass or other bariatric surgery, hypoglycemia is a recognized complication. In one study, 38% of gastric bypass patients showed episodes of low blood sugar when monitored with a continuous glucose sensor. About 12% reported symptoms serious enough to need help from another person.
The mechanism is called late dumping syndrome. After surgery, food moves through your digestive tract much faster than normal. When carbohydrates hit the small intestine quickly, your body releases an excessive burst of insulin. One to four hours later, that insulin surge has driven your blood sugar too low, causing sweating, dizziness, and fatigue. If you’ve had bariatric surgery and notice these symptoms after meals, this is likely the explanation.
Rare Causes
Certain tumors in the pancreas (called insulinomas) produce excess insulin, causing repeated episodes of low blood sugar. Inherited metabolic disorders can also impair your body’s ability to regulate glucose. These are uncommon but worth investigating if no other explanation fits, particularly if your episodes are frequent and severe.
How Symptoms Progress
Low blood sugar produces two waves of symptoms, and recognizing the first wave is important because it gives you time to act before things get worse.
The early warning signs come from your body’s stress response kicking in: sweating, shakiness, a racing heartbeat, anxiety, and sudden intense hunger. These are your body’s alarm bells, signaling that glucose is dropping and you need fuel.
If blood sugar continues to fall, the symptoms shift to your brain, which depends almost entirely on glucose for energy. You may feel weak, dizzy, or unusually tired. Concentration becomes difficult. Your behavior might seem off to people around you, sometimes resembling intoxication. Vision can blur. In severe cases, this can progress to confusion, seizures, loss of consciousness, or coma. The transition from “I feel shaky” to “I can’t think straight” can happen quickly, which is why treating early symptoms right away matters.
What to Do During an Episode
The standard approach is the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates, then wait 15 minutes and check your blood sugar again. If it’s still below 70 mg/dL, repeat. Good sources of 15 grams of carbs include four glucose tablets, four ounces of juice or regular soda, or a tablespoon of honey.
Avoid foods with fat or protein for this initial correction. Fat slows digestion, which delays the glucose from reaching your bloodstream. Once your blood sugar is back above 70 mg/dL, follow up with a balanced snack or meal to keep it stable.
Preventing Recurring Episodes
If your blood sugar drops frequently, the fix depends entirely on the cause. But several strategies help across the board:
- Eat regularly. Going more than four to five hours without food puts you at risk, especially if you’re prone to reactive hypoglycemia.
- Balance your meals. Pair carbohydrates with protein, healthy fat, or fiber. This slows the rate at which glucose enters your bloodstream and prevents the spike-and-crash cycle.
- Limit refined carbohydrates. White bread, sugary drinks, and sweets cause rapid blood sugar spikes that trigger an exaggerated insulin response.
- Be cautious with alcohol. Eat before or while drinking, and be aware that alcohol’s effect on blood sugar can last for several hours.
- Review your medications. If you suspect a medication is contributing, bring it up with your prescriber. Dose adjustments or timing changes can often help.
If you’re having repeated episodes without an obvious explanation, or if your blood sugar drops below 54 mg/dL, that warrants medical evaluation. Blood work during a symptomatic episode can reveal whether the problem is excess insulin production, a hormonal deficiency, or something else that needs targeted treatment.