A low blood glucose reading means your body doesn’t have enough sugar in your bloodstream to fuel your cells and brain. For most people, blood sugar below 70 mg/dL (3.9 mmol/L) is considered low, a condition called hypoglycemia. It can happen to people with diabetes who take insulin or certain medications, but it also affects people without diabetes for a variety of reasons.
Low glucose is usually easy to fix in the moment, but understanding why it’s happening matters. Repeated episodes or severely low readings can have real consequences.
How Your Body Normally Prevents Low Glucose
Your body has a built-in system for keeping blood sugar stable. When glucose starts dropping, your pancreas releases a hormone called glucagon. Glucagon works in three ways: it signals your liver to convert stored glucose back into a usable form and release it into your blood, it prevents your liver from absorbing more glucose so that what’s already circulating stays available, and it helps your body manufacture new glucose from non-carbohydrate sources like amino acids and fats.
During longer stretches without food, glucagon ramps up this glucose-manufacturing process even further. When this system works correctly, you can go hours between meals without your blood sugar dropping dangerously. Low glucose usually means something is interfering with this process, whether that’s medication, a medical condition, or an unusual metabolic response.
What Low Glucose Feels Like
The symptoms of low blood sugar come in two waves, and recognizing the early ones is important because it gives you time to act before things get worse.
The first wave is your body’s stress response kicking in. You’ll notice sweating, shakiness, a racing heart, anxiety, and sudden intense hunger. These are your body’s alarm signals, driven by the same adrenaline-like hormones that activate during a fight-or-flight response. Most people find these symptoms hard to ignore, which is the point.
If blood sugar keeps falling, you enter the second wave, where your brain starts running short on fuel. This causes weakness, fatigue, dizziness, difficulty concentrating, confusion, and blurred vision. Some people behave oddly enough during this stage that others mistake it for intoxication. In extreme cases, very low glucose can cause seizures, loss of consciousness, or coma.
Common Causes in People With Diabetes
If you take insulin or certain oral diabetes medications, low blood sugar is a well-known side effect. It typically happens when you take your usual dose but eat less than expected, skip a meal, exercise more intensely than usual, or drink alcohol. The medication lowers your blood sugar as designed, but without enough incoming food to balance it out, glucose drops too far.
People who manage their diabetes aggressively, aiming for very tight blood sugar control, face a higher risk of these episodes. Over time, frequent low blood sugar episodes create a dangerous pattern called hypoglycemia unawareness. Essentially, your body recalibrates its warning system. If you had symptoms yesterday when glucose hit 60 mg/dL, today you might not feel anything until it reaches 55. The threshold for warning symptoms keeps dropping, but the threshold for losing consciousness doesn’t. This means you can go from feeling fine to passing out with very little warning in between.
Severe hypoglycemia episodes carry serious consequences beyond the immediate danger of fainting. People who experience severe lows have a greater risk of heart attack or stroke in the following year, and recurrent episodes may contribute to long-term problems with brain and heart function.
Why It Happens Without Diabetes
Low blood sugar in people who don’t have diabetes is less common but does happen. The most frequent form is called reactive hypoglycemia, where blood sugar drops after eating rather than during fasting. It typically occurs about 2 hours after a meal, though it can happen up to 4 hours later.
The triggers are telling. Foods that cause a rapid spike in blood sugar, like white bread, white rice, white pasta, pastries, pancakes, candy, sweetened drinks, and honey, are common culprits. Your body overreacts to the sugar rush by releasing too much insulin, which then drives blood sugar down past normal levels. Alcohol can also trigger this response in some people. The exact mechanism isn’t fully understood, but the pattern is consistent enough that dietary changes are the primary treatment.
Other non-diabetes causes include certain medications (some of which aren’t related to blood sugar at all), excessive alcohol consumption on an empty stomach, liver or kidney disease, hormonal deficiencies, and rarely, tumors that produce insulin. Prolonged fasting or extreme calorie restriction can also deplete your glucose stores faster than your body can replenish them.
How to Treat a Low Glucose Episode
The standard approach is called the 15-15 rule. Eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat. Keep repeating until your levels return to your target range. Good sources of 15 grams of fast-acting carbs include 4 ounces of juice, a tablespoon of honey, or glucose tablets (which list the carb count on the label).
For severe episodes where someone has lost consciousness or is having a seizure, do not try to give them food or drink. They could choke. Emergency glucagon, available as a nasal spray or an auto-injector pen, is designed for exactly this situation. It works by forcing the liver to release stored glucose. If someone in your household has diabetes and uses insulin, having emergency glucagon on hand and knowing how to use it is essential.
Reactive Hypoglycemia and Diet
If your low glucose episodes follow meals rather than fasting, the fix is largely dietary. The goal is to avoid the sharp blood sugar spikes that trigger an insulin overcorrection. That means replacing simple carbohydrates with complex ones: whole grains instead of refined grains, pairing carbs with protein or fat to slow digestion, and eating smaller, more frequent meals rather than large ones.
Cutting back on sugary drinks, candy, and baked goods made with white flour makes the biggest difference for most people. These foods break down into glucose almost immediately, creating the exact spike-and-crash cycle that causes symptoms.
When Low Glucose Needs Further Investigation
A single mild episode after skipping lunch or overexerting yourself is usually nothing to worry about. But if you’re getting repeated low readings, experiencing symptoms regularly, or your glucose drops when you haven’t done anything obvious to cause it, that warrants investigation.
For episodes that happen after eating, one diagnostic approach is a mixed meal tolerance test. You drink a standardized meal replacement under medical supervision while your blood sugar is monitored at regular intervals over several hours. If your glucose drops below about 54 mg/dL (3.0 mmol/L) and you develop symptoms during the test, that confirms reactive hypoglycemia. For fasting-related low glucose, doctors may order blood work to check insulin levels, liver and kidney function, and hormone levels to identify the underlying cause.
Low blood sugar that happens without an obvious explanation, particularly in someone who doesn’t have diabetes and isn’t on medications that affect glucose, always deserves a closer look. The causes are usually manageable once identified, but ignoring repeated episodes risks both immediate safety problems and longer-term health effects.