What Is Considered A Low Blood Sugar Level?

A low blood sugar level is generally defined as a reading below 70 milligrams per deciliter (mg/dL) in people who have diabetes and are taking glucose-lowering medications. This threshold is used by major diabetes organizations and is based on the point at which the brain and body begin to show signs of glucose deprivation. For people without diabetes, blood sugar rarely drops below 70 mg/dL because the body has strong regulatory systems that keep it stable.

The number matters, but context matters just as much. A reading of 68 mg/dL in someone taking insulin is a clinical concern that needs action. The same reading in a healthy person who just finished a long run may be temporary and cause no symptoms at all. Understanding what counts as low — and why — helps you respond correctly.

What Is Considered A Low Blood Sugar Level?

For people with diabetes, the standard definition of hypoglycemia is a blood glucose reading below 70 mg/dL. This is called a “level 1” low. A “level 2” low is below 54 mg/dL, which is considered more serious and requires immediate treatment. A “level 3” low is any reading that causes severe symptoms — confusion, unconsciousness, or seizure — regardless of what the meter reads, because at that point the person cannot treat themselves.

These categories come from a consensus report published jointly by the American Diabetes Association and the European Association for the Study of Diabetes. The thresholds are not arbitrary. They reflect the glucose level at which counter-regulatory hormones like glucagon and epinephrine start surging, and the level at which cognitive function begins to decline in most people.

For people without diabetes, the picture is different. Fasting blood sugar normally stays between 70 and 99 mg/dL. The body regulates this tightly through the liver, which releases stored glucose when levels dip, and through hormones that signal the liver to produce more. True hypoglycemia in people without diabetes is uncommon and usually has a specific underlying cause.

What Are the Symptoms of Low Blood Sugar?

Symptoms fall into two groups: those caused by the body’s emergency response, and those caused by the brain not getting enough glucose.

The first group — sometimes called autonomic symptoms — happens because the body releases epinephrine (adrenaline) when it senses glucose dropping. These include:

• Shakiness or tremors
• Sweating, often sudden and clammy
• Heart palpitations or a racing heartbeat
• Anxiety or a feeling of dread
• Hunger
• Tingling around the mouth or fingers

The second group — neuroglycopenic symptoms — happens when the brain itself is running low on fuel. These include:

• Difficulty concentrating or confusion
• Slurred speech
• Blurred vision
• Dizziness or lightheadedness
• Unusual behavior or irritability
• Drowsiness

Not everyone gets the early warning signs. Some people — particularly those who have had diabetes for many years or who experience frequent lows — develop what is called hypoglycemia unawareness. Their body stops producing the early adrenaline symptoms, and the first sign of a low may be confusion or difficulty functioning. This is a meaningful clinical concern because it removes the window for self-treatment.

What Causes Blood Sugar to Drop?

In people with diabetes, the most common causes are well established:

• Too much insulin or diabetes medication relative to food intake
• Skipping or delaying meals after taking glucose-lowering medication
• Unusual physical activity without adjusting medication or food
• Drinking alcohol, which can block the liver from releasing glucose
• Kidney disease, which can slow the clearance of insulin from the body

Alcohol deserves a specific mention. The liver normally releases glucose between meals to keep blood sugar stable. Alcohol interrupts that process. A person who drinks heavily without eating can develop low blood sugar even without diabetes medications — though this is uncommon.

In people without diabetes, hypoglycemia has different causes. These include certain medications, critical illness, hormone deficiencies (such as adrenal insufficiency), severe liver disease, and a rare condition called insulinoma — a tumor of the pancreas that produces too much insulin. Reactive hypoglycemia, which occurs within a few hours after eating, is sometimes reported but is not consistently confirmed by clinical testing and remains debated among researchers.

How Is Low Blood Sugar Treated?

Treatment depends on how low the reading is and whether the person can swallow safely.

For a conscious person with a reading below 70 mg/dL, the standard approach is the “15-15 rule”: consume 15 grams of fast-acting carbohydrate, wait 15 minutes, and recheck. If still below 70 mg/dL, repeat. Fifteen grams of carbohydrate can come from 4 ounces of juice or regular soda, 1 tablespoon of sugar or honey, or 3 to 4 glucose tablets. These are established clinical recommendations from diabetes care guidelines.

After blood sugar returns above 70 mg/dL, eating a small snack containing protein and complex carbohydrates can help prevent another drop, especially if the next meal is more than an hour away.

For a person who is unconscious or cannot swallow, this becomes a medical emergency. Nothing should be given by mouth because of choking risk. Glucagon — available as an injection or nasal spray — is the standard treatment. Glucagon is a hormone that signals the liver to release stored glucose. It requires a prescription. If glucagon is not available, emergency services should be called.

For people without diabetes who experience documented hypoglycemia, treatment addresses the underlying cause rather than the glucose level alone. A single low reading without symptoms is generally not treated the same way as recurrent symptomatic lows.

When Should You Check Your Blood Sugar?

Checking frequency depends on your medications and your risk of lows. People who take insulin or sulfonylureas — a class of oral diabetes drugs that can cause hypoglycemia — need to check more often than those on medications that do not typically cause lows, such as metformin.

Common times to check include before meals, before driving, before and after exercise, and any time you feel symptoms. Checking before driving matters because low blood sugar impairs reaction time and judgment in ways that are similar to alcohol. Some diabetes guidelines recommend checking before every drive for people at risk of lows.

Continuous glucose monitors (CGMs) have changed how many people track glucose. These devices measure glucose in the fluid under the skin every few minutes and can alert users when levels are dropping. Research consistently shows that CGM use reduces the frequency and severity of low blood sugar events in people with type 1 diabetes and in those with type 2 diabetes who use insulin. However, CGM readings can lag behind blood glucose readings by several minutes, so a fingerstick confirmation is sometimes needed.

Can Low Blood Sugar Happen Without Diabetes?

Yes, but it is uncommon. The body has multiple backup systems to prevent glucose from dropping too low. For hypoglycemia to occur in someone without diabetes, one of those systems usually has to be disrupted.

Documented causes in people without diabetes include:

• Medications such as certain antibiotics, pain relievers, or heart medications
• Excessive alcohol intake without food
• Adrenal insufficiency — the adrenal glands do not produce enough cortisol, a hormone that helps maintain blood sugar
• Severe liver or kidney disease
• Insulinoma — a rare pancreatic tumor
• Bariatric surgery — some people develop low blood sugar after gastric bypass, a condition called post-bariatric hypoglycemia

The diagnostic process for hypoglycemia without diabetes typically involves a supervised fasting test in a clinical setting. This is not something to attempt at home. If you suspect you are having low blood sugar episodes and you do not have diabetes, that warrants a medical evaluation rather than self-diagnosis.

What Happens If Low Blood Sugar Goes Untreated?

Untreated low blood sugar can progress from uncomfortable to dangerous. Early symptoms like shakiness and sweating give way to confusion, coordination problems, and eventually loss of consciousness or seizures. The brain depends on glucose for fuel and has very limited storage of its own.

Severe hypoglycemia — the kind that requires someone else’s help — is the most serious acute complication of insulin therapy. It is also a major barrier to tight glucose control. Some people with diabetes run their blood sugar higher than recommended because they fear lows, which over time raises the risk of long-term complications.

There is also evidence that repeated severe lows may affect cognitive function over time, though the research here is mixed and the relationship is not fully understood. What is clear is that the immediate danger of an untreated severe low is real and potentially life-threatening.

How Can You Prevent Low Blood Sugar?

Prevention is built on matching medication to food and activity. For people with diabetes, this means:

• Not skipping meals after taking insulin or sulfonylureas
• Checking blood sugar before exercise and adjusting food or medication as discussed with your care team
• Limiting alcohol or always eating when drinking
• Keeping fast-acting carbohydrate within reach at all times
• Wearing a medical alert ID
• Reviewing your medication regimen with your doctor if you have frequent lows

If you experience lows regularly, that is information your doctor needs. It may mean your medication dose needs adjustment. Frequent lows are not something to accept as normal.

For people without diabetes, prevention means addressing the underlying cause. There is no general prevention strategy for a condition that should not normally occur.