Low blood sugar, called hypoglycemia, is when your blood glucose drops below 70 mg/dL. At that level, your body starts sending warning signals like shakiness, sweating, and hunger. A more serious drop below 54 mg/dL can affect your brain’s ability to function and requires immediate action.
How Blood Sugar Is Classified
The American Diabetes Association uses a three-level system to categorize low blood sugar. Level 1 is a reading between 54 and 69 mg/dL. You’ll likely notice symptoms, but you can treat it yourself. Level 2 is anything below 54 mg/dL, the point where your brain starts running short on fuel. Level 3 isn’t defined by a specific number. It’s any episode severe enough that you need someone else’s help to recover, whether that means you’re confused, unconscious, or unable to eat on your own.
What Happens in Your Body
Your body has a built-in system for keeping blood sugar stable. After you eat, your pancreas releases insulin to move glucose out of your bloodstream and into your cells. Between meals, a second hormone called glucagon does the opposite: it signals your liver to release stored glucose back into your blood. In a healthy person, these two hormones work like a thermostat, keeping glucose within a narrow range.
When blood sugar drops too low, your body treats it as an emergency. Your adrenal glands release adrenaline, which is why you feel shaky, anxious, and sweaty. That adrenaline response is actually protective. It’s your body’s alarm system telling you to eat something. If glucose keeps falling, your brain, which depends almost entirely on glucose for energy, starts to malfunction. That’s when confusion, slurred speech, and blurred vision set in.
Early Warning Signs vs. Dangerous Symptoms
Symptoms fall into two broad categories. The first group comes from your body’s adrenaline response: sweating, shakiness, a racing heart, anxiety, and sudden intense hunger. These tend to appear first and serve as an early warning that your blood sugar is dropping.
The second group comes from your brain not getting enough glucose. These symptoms are more concerning: weakness, dizziness, difficulty concentrating, confusion, inappropriate behavior (sometimes mistaken for drunkenness), and blurred vision. In extreme cases, this can progress to seizures, loss of consciousness, or coma. If you notice the adrenaline-type symptoms and act on them, you can usually avoid the more dangerous brain-related ones entirely.
Common Causes
The most common cause of low blood sugar is excess insulin, whether your body overproduces it or you take too much through injection. For people with diabetes, the usual triggers are taking too much medication, skipping or delaying meals, exercising more than planned, or drinking alcohol without eating. Insulin and certain oral diabetes medications (sulfonylureas) carry the highest risk.
Low blood sugar without diabetes is uncommon but does happen. It generally falls into two patterns. Reactive hypoglycemia occurs a few hours after eating, often because your body releases too much insulin in response to a meal. Fasting hypoglycemia happens when you haven’t eaten for an extended period. Other hormonal and metabolic conditions, including problems with the liver or kidneys, can also interfere with your body’s ability to maintain stable glucose levels. Heavy alcohol consumption is another trigger because alcohol blocks the liver from releasing stored glucose.
How Low Blood Sugar Is Diagnosed
For people with diabetes who monitor their glucose, a low reading on a meter or continuous glucose monitor is usually straightforward to interpret. For people without diabetes, diagnosis follows a framework called Whipple’s triad. All three of these must be present: symptoms consistent with low blood sugar, a low glucose level confirmed by a lab test at the time symptoms are occurring, and resolution of those symptoms once glucose is raised. Meeting all three criteria rules out other conditions that can mimic the same symptoms, like anxiety or inner ear problems.
How to Treat a Low in the Moment
The standard approach is the 15-15 rule. Eat 15 grams of fast-acting carbohydrate, then wait 15 minutes. Good options for roughly 15 grams include:
- 3 glucose tablets
- Half a cup (4 oz) of fruit juice or regular soda
- 6 or 7 hard candies
- 1 tablespoon of sugar
After 15 minutes, recheck your blood sugar. If it’s still below 70 mg/dL, repeat with another 15 grams. Once your levels are back in a safe range, eating a small snack or meal with protein and complex carbohydrates helps prevent another drop.
For severe episodes where someone is unconscious or unable to swallow, bystanders should not try to put food or liquid in the person’s mouth. This is where emergency glucagon comes in. It’s a hormone that triggers the liver to dump stored glucose into the bloodstream, typically raising levels within 5 to 20 minutes. Since 2019, glucagon has been available as a nasal spray (for ages 4 and up), which is significantly easier for bystanders to administer than the older injectable kits. The injectable versions require mixing powder with liquid and using a syringe, and studies found that caregivers frequently made errors during the high-stress moment of an emergency.
Hypoglycemia Unawareness
One of the more dangerous complications of repeated low blood sugar is that your body can stop warning you it’s happening. This condition, called hypoglycemia unawareness, means the adrenaline-driven symptoms like shaking and sweating become muted or disappear entirely. You skip straight to the brain-related symptoms, or you may not notice anything at all until your glucose is dangerously low.
About 25% of people with type 1 diabetes experience hypoglycemia unawareness. Among people with type 2 diabetes who use insulin or sulfonylureas, estimates range from 10 to 15%, and continuous glucose monitors are revealing the true number may be higher. If you’ve had repeated lows, particularly at night when you can’t notice symptoms, the risk of unawareness increases over time. Continuous glucose monitors with low-glucose alarms are one of the most effective tools for catching drops you might otherwise miss.
Long-Term Effects of Repeated Lows
A single mild episode that you catch and treat quickly is not dangerous. The concern is with frequent or severe episodes over months and years. Recurrent hypoglycemia can contribute to long-term problems with both brain and heart function. Severe lows, particularly those involving seizures or loss of consciousness, carry the most risk. This is one reason diabetes management aims not just for lower blood sugar overall but for stable blood sugar, minimizing the swings in both directions.