Blood sugar drops below normal when your body uses glucose faster than it can replace it, or when something interferes with the hormones that keep glucose steady. For people with diabetes, a reading below 70 mg/dL counts as low. For people without diabetes, the threshold is lower, around 55 mg/dL. The causes range from simple things like skipping a meal or drinking alcohol to medical conditions that need attention.
How Your Body Normally Keeps Blood Sugar Stable
Your liver stores glucose and releases it between meals to keep your blood sugar in a safe range. Hormones from the pancreas, adrenal glands, and pituitary gland coordinate this process. Insulin lowers blood sugar after you eat, while other hormones like glucagon raise it when levels start to dip. When any part of this system misfires, whether from medication, illness, or a hormonal imbalance, blood sugar can fall too low.
Common Everyday Causes
The most straightforward reason for low blood sugar is not eating enough or waiting too long between meals. Your brain alone burns through roughly 120 grams of glucose per day, so skipping meals or eating very little leaves your body short on fuel. Pairing a skipped meal with intense physical activity makes the drop even steeper because working muscles pull glucose from the bloodstream at a much higher rate than resting ones.
Alcohol is another frequent trigger. When your liver is busy processing alcohol, it can’t release stored glucose efficiently. The chemical breakdown of alcohol shifts the liver’s internal chemistry in a way that directly blocks glucose production. This is why low blood sugar can hit hours after drinking, especially if you drank on an empty stomach or had several drinks without eating.
Medications That Lower Blood Sugar
If you take diabetes medication, it’s the most likely explanation. Insulin and a class of drugs called sulfonylureas (like glipizide or glyburide) are the most common culprits because they actively push blood sugar down. Taking too much, eating less than usual, or exercising more than planned after a dose can tip you into hypoglycemia.
But diabetes drugs aren’t the only ones that cause this. Several medications prescribed for entirely different conditions can lower blood sugar as a side effect. These include certain antibiotics like levofloxacin, the antimalarial drug quinine, some heart rhythm medications, and even the pain reliever indomethacin. Beta-blockers like propranolol deserve special mention because they can both lower blood sugar and mask the early warning symptoms, making a drop harder to notice.
Reactive Hypoglycemia After Meals
Some people experience low blood sugar not from skipping meals but within a few hours after eating. This is called reactive hypoglycemia, and it typically hits within four hours of a meal. Your body overproduces insulin in response to the food you ate, especially if the meal was heavy in simple carbohydrates like white bread, sugary drinks, or pastries. The excess insulin clears too much glucose from your blood, leaving you shaky and lightheaded.
People who have had gastric bypass or other bariatric surgery are particularly prone to this because food moves into the small intestine faster than normal, triggering a rapid insulin spike. Avoiding sugary foods and processed simple carbohydrates, especially on an empty stomach, is one of the most effective ways to prevent these post-meal crashes. Eating smaller, more frequent meals that include protein and fiber slows glucose absorption and keeps insulin responses more proportional.
Exercise and Delayed Blood Sugar Drops
During exercise, your muscles can increase glucose uptake dramatically. Your liver ramps up glucose production to compensate, but if production can’t keep pace with demand, blood sugar falls. This is most likely during prolonged exercise or when you work out intensely shortly after eating a high-carbohydrate meal, which can cause what researchers call “rebound hypoglycemia.”
The timing can be deceiving. Your blood sugar might stay stable during the workout itself, then drop afterward as your muscles continue pulling in glucose to replenish their stores. If you’ve noticed low blood sugar symptoms an hour or two after a hard workout, this delayed effect is the likely reason.
Medical Conditions Behind Low Blood Sugar
When low blood sugar keeps recurring and you can’t trace it to meals, medications, or exercise, an underlying medical condition may be involved. Several organ systems can contribute:
- Liver disease. Severe hepatitis, cirrhosis, and other serious liver conditions impair your liver’s ability to store and release glucose, its primary job in blood sugar regulation.
- Kidney disease. Your kidneys help clear insulin from the bloodstream. When they’re not functioning well, insulin lingers longer than it should, continuing to push blood sugar down.
- Adrenal or pituitary disorders. These glands produce hormones that tell the liver when to release glucose. If they’re underperforming due to a tumor or insufficiency, the signal weakens and blood sugar can drop.
- Severe infections and advanced heart disease. Critical illness increases glucose demand across the body while simultaneously impairing the systems that produce it.
A rare but important cause is an insulinoma, a small tumor on the pancreas that continuously secretes insulin regardless of what your blood sugar is doing. These tumors keep pushing insulin out even when it’s not needed, causing repeated episodes of low blood sugar, particularly during fasting. Diagnosis involves blood tests measuring insulin and glucose levels simultaneously, followed by imaging to locate the tumor.
How to Recognize the Warning Signs
Low blood sugar produces symptoms in two waves. The early warning signs come from your body’s stress response kicking in: sweating, a pounding or racing heart, trembling, anxiety, and sudden intense hunger. These symptoms are your body’s alarm system, and they typically appear first.
If blood sugar continues to fall, brain-related symptoms take over because the brain depends almost entirely on glucose for fuel. These include confusion, difficulty concentrating, irritability, blurred vision, and slurred speech. In severe cases, seizures or loss of consciousness can follow. The progression from early stress symptoms to brain symptoms is what makes it important to act quickly when you notice the first signs.
What to Do When Blood Sugar Drops
The standard approach is the 15-15 rule recommended by the CDC: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat the process. Good sources of 15 grams of carbs include four glucose tablets, four ounces of juice, or a tablespoon of honey.
Once your blood sugar is back above 70, eat a small meal or snack that includes some protein and complex carbohydrates to keep it stable. A handful of nuts with a piece of fruit or cheese and crackers works well. The fast-acting sugar gets you out of the danger zone, and the follow-up snack prevents another drop.
If episodes keep happening and you’re not on medications known to cause them, that pattern is worth investigating. Repeated low blood sugar without an obvious trigger, particularly readings below 54 mg/dL (classified as Level 2 hypoglycemia), points toward something that needs medical evaluation rather than just a snack.