Low blood sugar, or hypoglycemia, happens when your blood glucose drops below 70 mg/dL. If you don’t have diabetes, this can feel especially confusing because there’s no obvious reason your body should struggle to keep glucose levels stable. But several common factors can trigger it, from what you ate (or didn’t eat) to how your liver, kidneys, and hormones are functioning behind the scenes.
Your Blood Sugar Drops After Eating
One of the most common patterns, especially in people without diabetes, is reactive hypoglycemia. Your blood sugar drops within four hours after a meal, typically peaking around the two- to three-hour mark. The exact mechanism isn’t always clear, but it often relates to your body overshooting its insulin response. You eat, your blood sugar rises, your pancreas releases insulin to bring it down, and sometimes it brings it down too far.
Meals heavy in refined carbohydrates tend to make this worse. A big plate of white pasta or a sugary drink spikes your blood sugar fast, which triggers a larger insulin surge. People who are more insulin-sensitive may be especially prone to these dips. Alcohol can also play a role, and people who’ve had gastric bypass or other bariatric surgery are at higher risk because food moves through their digestive system differently.
You Haven’t Eaten Enough
This one sounds obvious, but skipping meals, fasting too long, or chronically undereating is a straightforward cause of low blood sugar. Your body stores glucose in the liver and muscles as glycogen, and those reserves can carry you through several hours without food. But once they’re depleted, your blood sugar drops. Prolonged starvation, severe calorie restriction, or eating disorders like anorexia nervosa can drain glycogen stores completely and cause repeated episodes.
Exercise Is Using Up Your Fuel
During physical activity, your muscles dramatically increase how much glucose they pull from the bloodstream. Normally, your liver ramps up glucose production to keep pace, but sometimes it can’t keep up, particularly during intense or prolonged exercise. Two scenarios are especially risky: starting vigorous exercise shortly after eating a high-carbohydrate meal (which can cause a rebound drop) and exercising for extended periods as fuel stores run out.
People who are more insulin-sensitive tend to see steeper drops during post-meal exercise. In studies tracking glucose levels during exercise after eating, the most insulin-sensitive individuals consistently hit the lowest blood sugar readings. This doesn’t mean exercise is dangerous, but it does explain why some people feel shaky or lightheaded during or after a hard workout.
Alcohol Blocks Your Liver’s Backup System
Your liver is your body’s glucose factory. When blood sugar starts to dip, the liver converts stored glycogen into glucose and releases it into your bloodstream. Alcohol directly impairs this process. Even in people with no underlying liver disease, drinking can suppress the liver’s ability to produce glucose, leading to hypoglycemia. This is especially likely if you drink without eating, because your glycogen stores are already low and the one organ that could rescue your blood sugar is busy processing alcohol instead.
Certain Medications Can Lower Blood Sugar
Diabetes medications are the most obvious culprits, but several non-diabetes drugs can also push blood sugar down. Certain antibiotics used to treat infections, some heart rhythm medications, beta-blockers (used for blood pressure and anxiety), and even some pain relievers have been linked to hypoglycemia. If your kidneys aren’t working well, the problem compounds because your body can’t clear medications efficiently, letting them build up and exert a stronger blood-sugar-lowering effect than intended.
If you’ve recently started a new medication and notice symptoms like shakiness, sweating, or sudden hunger, the timing may not be a coincidence.
Hormonal Imbalances
Cortisol, produced by your adrenal glands, plays a key role in helping your body convert food into energy and keeping blood sugar stable between meals. In conditions like Addison’s disease (adrenal insufficiency), cortisol production drops, and low blood sugar becomes a recurring problem. People with secondary adrenal insufficiency, where the pituitary gland fails to signal the adrenals properly, are even more likely to experience hypoglycemia.
An adrenal crisis, the most severe form, can cause dangerously low blood sugar alongside low blood pressure, and it requires emergency treatment.
Liver and Kidney Disease
Because the liver is central to glucose production, severe liver conditions like hepatitis or cirrhosis can directly cause hypoglycemia. The liver simply can’t manufacture enough glucose to meet your body’s needs. Kidney disease contributes in a different way: the kidneys help clear medications and insulin from your bloodstream, so when they’re impaired, blood-sugar-lowering substances linger longer than they should. Advanced heart disease and severe infections can also overwhelm the body’s glucose regulation.
Rare but Worth Knowing: Insulinomas
In uncommon cases, a small tumor on the pancreas called an insulinoma produces excess insulin regardless of what your blood sugar is doing. The hallmark is a pattern called the Whipple triad: you develop symptoms of hypoglycemia, a blood test confirms your glucose is genuinely low at that moment, and the symptoms resolve when you eat something sugary. About 85% of people with an insulinoma experience symptoms like blurred vision, palpitations, weakness, or sweating. Some develop confusion, abnormal behavior, or even seizures during severe episodes.
Diagnosis typically involves a supervised fasting test lasting up to 72 hours to catch the pancreas producing insulin when it shouldn’t be. Imaging can then locate the tumor, and the vast majority are benign and surgically removable.
What Low Blood Sugar Feels Like
Symptoms typically come in waves. Early on, your body releases stress hormones to try to raise blood sugar, which causes sweating, shakiness, a pounding heart, and sudden intense hunger. If glucose continues to drop, your brain starts running short on fuel, leading to confusion, difficulty concentrating, irritability, and blurred vision. Below 54 mg/dL is considered severe hypoglycemia, which can cause loss of consciousness or seizures.
How to Bring Blood Sugar Back Up
The standard approach is the 15-15 rule: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar. If it’s still below 70 mg/dL, repeat. Good options include four glucose tablets, half a cup of juice, or a tablespoon of honey. Young children, especially toddlers, typically need less than 15 grams. Once your blood sugar stabilizes, follow up with a small snack or meal that includes protein and complex carbohydrates to prevent another drop.
If episodes are frequent or you can’t identify a clear trigger like skipping meals or intense exercise, tracking when your symptoms occur relative to meals, activity, and medications can help pinpoint the pattern. Recurrent unexplained hypoglycemia, especially if it’s happening while fasting or waking you up at night, is worth investigating further with blood work to check hormone levels, liver and kidney function, and insulin activity.