A blood glucose level below 70 mg/dL (3.9 mmol/L) is generally considered low. This threshold applies whether you have diabetes or not, though the exact number that triggers symptoms varies from person to person. Below 54 mg/dL is classified as severely low and requires immediate action.
Where Low Begins: The Key Numbers
Normal fasting blood glucose falls below 100 mg/dL. Once it drops under 70 mg/dL, you’re in the range the CDC and most medical guidelines define as hypoglycemia. That 70 mg/dL line isn’t a hard cutoff where everyone suddenly feels terrible. Some people notice symptoms at 75, others feel fine until they hit 60. But 70 is the number that should prompt you to act.
For people without diabetes, the diagnostic bar is slightly different. Clinicians typically look for glucose below 60 mg/dL along with symptoms to confirm clinically significant hypoglycemia. This is sometimes called Whipple’s triad: low blood sugar, symptoms that match, and those symptoms going away once blood sugar comes back up. The reason for the lower threshold in non-diabetic cases is that healthy bodies are usually very good at preventing glucose from dipping dangerously, so when it happens, something meaningful is going on.
Below 54 mg/dL is considered severe hypoglycemia regardless of who you are. At this level, your brain isn’t getting enough fuel to function normally, and the risk of confusion, loss of consciousness, or seizures climbs sharply.
What Low Blood Sugar Feels Like
The earliest symptoms come from your body’s stress response. When glucose starts dropping, your system floods with adrenaline to try to push stored sugar into your bloodstream. That’s why the first signs often feel like anxiety: shaking, sweating, a racing heartbeat, and sudden hunger. You might feel irritable or jittery for no obvious reason. These are your warning signals, and they’re your best window for correcting the problem easily.
If blood sugar keeps falling, symptoms shift from adrenaline-driven to brain-driven. Your brain is the most glucose-hungry organ in your body, and when it’s starved, you’ll notice confusion, difficulty concentrating, slurred speech, blurred vision, and coordination problems. At the severe end, this progresses to fainting, seizures, or loss of consciousness. Some people, particularly those who’ve had frequent low blood sugar episodes, lose the ability to feel early warning signs altogether, a condition called hypoglycemia unawareness, which makes regular monitoring even more important.
Common Causes
For people with diabetes, the most common trigger is a mismatch between medication and food. Taking insulin or certain oral diabetes medications and then skipping a meal, eating less than planned, or exercising more than usual can all send glucose plummeting. Alcohol makes this worse because it interferes with the liver’s ability to release stored glucose.
Several classes of diabetes medications carry a higher risk of causing lows. Sulfonylureas and glinides directly stimulate the pancreas to release more insulin, which can overshoot your actual needs. Metformin combined with sulfonylureas raises risk further. Even newer SGLT2 inhibitors can contribute, especially when paired with sulfonylureas.
Non-diabetes medications can also cause unexpected drops. Certain antibiotics, some heart rhythm drugs, beta-blockers in overdose, and even some pain relievers have been linked to drug-induced hypoglycemia. If you’ve recently started a new medication and notice symptoms of low blood sugar, that connection is worth investigating.
For people without diabetes, low blood sugar is less common but does happen. Reactive hypoglycemia occurs within four hours after a meal, typically when the body overproduces insulin in response to a large carbohydrate load. Other causes include prolonged fasting, excessive alcohol consumption, certain liver or kidney conditions, and rarely, tumors that produce insulin.
How to Treat a Low Glucose Episode
The standard approach is called the 15-15 rule: eat 15 grams of fast-acting carbohydrate, then wait 15 minutes. Good options include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. These are simple sugars that hit your bloodstream quickly. If you don’t feel better after 15 minutes, eat another 15 grams and wait again.
What you don’t want to reach for is something high in fat or protein, like a candy bar or peanut butter. Fat slows digestion and delays the sugar from reaching your blood when you need it most. Save the balanced snack for after your glucose has come back up, to keep it stable.
Once your blood sugar returns above 70 mg/dL and symptoms have cleared, eating a small meal or snack with protein and complex carbohydrates helps prevent another drop. Think crackers with cheese, a handful of nuts with fruit, or a half sandwich.
When a Low Becomes an Emergency
Severe hypoglycemia is a medical emergency. If you become confused, lose consciousness, have a seizure, or can’t swallow safely, the 15-15 rule is no longer enough. This is where glucagon comes in. Glucagon is a hormone that signals the liver to dump stored sugar into the bloodstream, and it’s available in ready-to-use nasal sprays and injectable kits. Anyone who’s at risk for severe lows should keep glucagon accessible, and the people around them should know where it is and how to use it.
Call 911 if glucagon isn’t available, if the person doesn’t respond to glucagon within about 15 minutes, or if you’re unsure what to do. Never try to force food or liquid into the mouth of someone who is unconscious or too confused to swallow, as this creates a choking risk.
Preventing Frequent Lows
If you’re monitoring your glucose regularly and seeing numbers below 70 more than a couple of times a week, your medication timing, doses, or eating patterns likely need adjusting. Keeping a log of when lows happen, what you ate beforehand, and what activity you were doing helps identify patterns.
Consistent meal timing makes a significant difference. Skipping meals or going long stretches without eating is one of the most reliable triggers for a drop. If you exercise, checking glucose before and after helps you learn how different activities affect your levels. Intense or prolonged workouts can lower blood sugar for hours afterward, sometimes even into the next day.
For reactive hypoglycemia in people without diabetes, the fix is often dietary: smaller, more frequent meals with balanced macronutrients instead of large carbohydrate-heavy ones. Pairing carbohydrates with protein and healthy fat slows their absorption and prevents the insulin spike that causes the rebound crash.