For someone with diabetes, blood sugar below 70 mg/dL is considered low. This threshold, called hypoglycemia, applies whether you have type 1 or type 2 diabetes. Below 54 mg/dL is classified as severely low and requires immediate action, often from another person.
Why 70 mg/dL Is the Cutoff
At 70 mg/dL, your body starts releasing stress hormones to push glucose back up. This is where most people begin feeling the first warning signs. The number isn’t arbitrary: it’s the point where your brain’s fuel supply gets tight enough to trigger a defensive response. For context, a normal fasting blood sugar sits between 70 and 100 mg/dL, so hypoglycemia begins right at the lower edge of the typical range.
The severity breaks down into levels. Between 54 and 70 mg/dL, you can usually treat the episode yourself. Below 54 mg/dL, your brain function becomes impaired enough that you may need someone else to help you. At this stage, confusion, loss of coordination, and even loss of consciousness are possible.
Early Warning Signs vs. Dangerous Symptoms
Hypoglycemia symptoms arrive in a predictable sequence. The early signs come from your body’s adrenaline response: sweating, a racing or pounding heart, trembling hands, sudden anxiety, and intense hunger. These symptoms are uncomfortable but useful. They’re your built-in alarm system telling you to eat something now.
If blood sugar keeps dropping, the symptoms shift from adrenaline-driven to brain-driven. This is when things get more dangerous. You may notice confusion, difficulty concentrating, irritability, or slurred speech. In severe cases, hallucinations, inability to move one side of the body, seizures, and coma can occur. The key distinction: early symptoms feel physical, while later symptoms affect your thinking and behavior, which makes them harder to recognize on your own.
What Causes Lows in People With Diabetes
The most common trigger is a mismatch between your medication and your food intake or activity level. Specifically:
- Too much insulin or certain oral medications. Sulfonylureas are a class of diabetes pills particularly known for causing lows.
- Skipping or delaying meals. If your medication is already working to lower blood sugar and you don’t eat on schedule, glucose can drop fast.
- More physical activity than usual. Exercise pulls glucose out of your bloodstream for energy. If you increase your activity without adjusting food or medication, a low can follow.
- Alcohol, especially on an empty stomach. Alcohol blocks your liver from releasing stored glucose, and it can cause delayed lows hours after drinking.
People using insulin, particularly those with type 1 diabetes, face the highest risk. But anyone on sulfonylureas or similar medications that actively push blood sugar down can experience hypoglycemia. Medications like metformin, by contrast, rarely cause lows on their own.
How to Treat a Low: The 15-15 Rule
The standard approach is simple: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process. Fifteen grams of fast-acting carbs looks like 4 glucose tablets, a small tube of glucose gel, 4 ounces of juice, or about a tablespoon of sugar dissolved in water.
The “fast-acting” part matters. A candy bar or a sandwich contains fat and protein that slow digestion. You need something that hits your bloodstream quickly. Once your blood sugar stabilizes above 70, follow up with a more substantial snack or meal to keep it from dropping again.
Severe Lows Require Emergency Glucagon
When blood sugar drops so low that a person can’t swallow safely, is confused, or has lost consciousness, they can’t eat their way out of it. This is when emergency glucagon becomes necessary. Glucagon is a hormone that tells the liver to dump stored glucose into the bloodstream, and it works within minutes.
Modern glucagon products are designed so that family members, coworkers, or bystanders can use them without medical training. Options include a nasal powder you spray into one nostril (no inhalation needed) and pre-filled auto-injectors that work similarly to an EpiPen. Older kits require mixing a powder with liquid before injection, which is harder to manage in a crisis. If you use insulin or have experienced severe lows before, keeping a glucagon product nearby and making sure the people around you know where it is and how to use it can be lifesaving.
Low Blood Sugar During Sleep
Nocturnal hypoglycemia is particularly tricky because you’re not awake to notice the early warning signs. Clues that a low happened overnight include waking up drenched in sweat, having vivid nightmares, feeling unusually groggy or headachy in the morning, or a bed partner noticing restlessness, shaking, or sudden changes in your breathing pattern.
A continuous glucose monitor can be especially helpful here. These devices check your glucose every five minutes and can sound an alarm to wake you if levels start trending too low. Without one, setting an alarm to check blood sugar around 2 or 3 a.m. for a period of time can help you and your care team identify a pattern and adjust your medication timing or dosing accordingly.
Hypoglycemia Unawareness
One of the more unsettling complications of repeated lows is that your body can stop warning you. After enough episodes, the adrenaline response that produces sweating, shaking, and a racing heart becomes blunted. Your blood sugar drops, but you feel fine until it reaches a level where brain function is already impaired. This is called hypoglycemia unawareness, and it significantly raises the risk of a severe episode.
The condition is more common in people who have had diabetes for many years and in those who experience frequent mild lows. The good news is that it can often be partially reversed. Carefully avoiding any hypoglycemia for several weeks can help restore your body’s warning signals. This typically involves temporarily raising your blood sugar targets so your body recalibrates what “normal” feels like, then gradually tightening control again. Blood glucose awareness training, which teaches you to recognize subtler cues your body gives during a low, can also help.