Your blood glucose drops below normal when your body uses sugar faster than it can replace it, or when something interferes with the hormones and organs that keep your blood sugar steady. A reading below 70 mg/dL is considered low, and anything below 54 mg/dL is serious enough to need immediate action. The causes range from everyday factors like skipping meals or drinking alcohol to medication side effects and, less commonly, underlying health conditions.
What Counts as Low Blood Sugar
Normal fasting blood glucose generally sits between 70 and 100 mg/dL. Below 70, you’re in mild hypoglycemia territory. Your body can usually compensate at this level, but you’ll likely start noticing symptoms. Below 54 mg/dL, the brain starts running short on fuel, and symptoms become more pronounced and harder to ignore. At the most severe level, blood sugar drops far enough that you may need someone else’s help to recover, regardless of the exact number on the meter.
How Low Blood Sugar Feels
The symptoms come in two waves, driven by different parts of your body responding to the sugar shortage. Early on, your nervous system fires off alarm signals: trembling, sweating, anxiety, feeling warm, and sometimes nausea. These are your body’s way of telling you to eat something, fast.
If blood sugar keeps falling, the brain itself starts struggling. You might have trouble concentrating, feel drowsy or weak, slur your words, get dizzy, or become confused. These brain-related symptoms are the more dangerous ones because they can impair your ability to recognize what’s happening and treat it yourself. Some people experience both sets of symptoms at once, while others, particularly those who have frequent low blood sugar episodes, may lose the early warning signs entirely.
Common Causes If You Have Diabetes
The most frequent reason for low glucose in people with diabetes is a mismatch between medication and what the body actually needs at that moment. Taking too much insulin, delaying a meal after your usual dose, or being more active than expected can all tip the balance. Certain oral diabetes medications that stimulate insulin production carry the same risk.
Exercise creates a particularly tricky window. Blood sugar can drop during physical activity, but the risk doesn’t end when you stop. Research on people with type 1 diabetes shows hypoglycemia risk peaks about an hour after exercise, then rises again 5 to 10 hours later. That delayed drop catches many people off guard, especially overnight after an active afternoon or evening.
Causes If You Don’t Have Diabetes
Low blood sugar in people without diabetes is less common but not rare. The causes generally fall into two categories: drops that happen after eating (reactive hypoglycemia) and drops that happen during fasting.
Reactive Hypoglycemia
This type hits within four hours of a meal. Your pancreas releases more insulin than needed in response to the food you ate, overshooting the mark and pulling blood sugar down too far. The exact reason this happens isn’t always clear, but it tends to be linked to meals heavy in refined carbohydrates. People who’ve had gastric bypass or other stomach surgery are especially prone to it because food moves into the small intestine faster, triggering a sharper insulin spike.
Fasting Hypoglycemia
When blood sugar drops between meals or overnight, the cause is usually something interfering with your liver’s ability to release stored glucose or with the hormones that regulate the process. Several things can do this:
- Alcohol. Your liver prioritizes breaking down alcohol over maintaining blood sugar. Drinking reduces your liver’s glucose production by roughly 12%, and the specific process of building new glucose molecules drops by about 45% in the five hours after drinking. This is why low blood sugar can hit hours after your last drink, especially if you haven’t eaten.
- Medications. Several non-diabetes drugs can lower blood sugar as a side effect. These include certain beta-blockers used for blood pressure, some heart rhythm medications, specific antibiotics (particularly fluoroquinolones), and certain anti-inflammatory painkillers. If your low readings started around the same time as a new prescription, that connection is worth exploring.
- Liver or kidney disease. Both organs play central roles in blood sugar regulation. The liver stores and releases glucose; the kidneys help clear insulin from the body. When either is compromised, the system can fall out of balance.
- Adrenal or pituitary problems. Hormones like cortisol and growth hormone act as counterweights to insulin, preventing blood sugar from dropping too low. If your adrenal glands or pituitary gland aren’t producing enough of these hormones, that safety net weakens.
- Insulinoma. This is a rare, usually benign tumor in the pancreas that produces insulin continuously, even when blood sugar is already low. Most insulinomas are small, single growths that can be surgically removed. They’re uncommon, but worth knowing about if you’re having repeated unexplained episodes of low blood sugar, especially while fasting.
Skipping Meals and Erratic Eating
The simplest and most overlooked cause is just not eating enough or waiting too long between meals. Your body burns through its readily available glucose within a few hours. After that, it relies on the liver to release stored glucose, but that supply is finite, especially if you went to bed without much dinner or skipped breakfast. Combine irregular eating with intense physical activity or alcohol, and the risk compounds quickly.
What to Do When It Drops
The standard approach is called the 15-15 rule. Eat or drink 15 grams of fast-acting carbohydrates: four glucose tablets, half a cup of juice, or a tablespoon of honey. Wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat. Keep going until you’re back in a normal range, then eat a small meal or snack to keep it stable.
The key is using simple carbohydrates, not foods high in fat or protein. A candy bar or peanut butter crackers might seem like a reasonable choice, but fat slows digestion and delays the glucose from reaching your bloodstream. You want something your body can absorb quickly.
If someone’s blood sugar has dropped so low that they’re confused, unconscious, or unable to swallow safely, they need glucagon, an injectable or nasal spray medication that signals the liver to dump its glucose stores into the blood. Anyone who takes insulin or has frequent severe episodes should have this on hand, and the people around them should know where it is and how to use it.
Patterns Worth Paying Attention To
A single episode of mild low blood sugar after skipping lunch is usually nothing to worry about. What matters more is the pattern. Repeated episodes, drops that happen without an obvious trigger like missed meals or exercise, or symptoms that consistently occur at the same time of day all suggest something beyond simple dietary timing. Fasting-related drops in particular, ones that wake you up at night or hit before breakfast, are more likely to point toward a hormonal issue, liver problem, or medication effect that needs investigation.
If you’re tracking your glucose with a monitor, look at when the lows cluster. Post-meal drops suggest reactive hypoglycemia. Overnight or early-morning lows suggest fasting hypoglycemia. That distinction helps narrow down the cause considerably and gives your doctor a clearer starting point for testing.