Low blood sugar, or hypoglycemia, can be a sign of several underlying conditions ranging from medication side effects and hormonal imbalances to liver disease, kidney problems, or rarely, a pancreatic tumor. A blood sugar reading below 70 mg/dL is considered low, while anything below 54 mg/dL is more serious and may require immediate help. If you’re experiencing repeated episodes, your body is signaling that something needs attention.
Diabetes Medication Effects
The most common reason for low blood sugar is diabetes treatment itself. Insulin and a class of oral medications called sulfonylureas are the biggest culprits because they actively push blood sugar down, sometimes more than intended. This can happen if you take your usual dose but eat less than normal, skip a meal, exercise harder than expected, or drink alcohol.
Several other medications can also trigger drops in blood sugar, including certain heart rhythm drugs, some antibiotics, and pain relievers like indomethacin. Beta-blockers deserve special mention because they can both contribute to low blood sugar and mask the early warning signs your body would normally give you, like a racing heart or trembling hands.
Hormonal and Endocrine Disorders
Your body has a built-in defense system against low blood sugar. When glucose starts to drop, hormones like cortisol and growth hormone kick in to tell the liver to release stored sugar and make new glucose. If the glands that produce these hormones aren’t working properly, that safety net fails.
Adrenal insufficiency, where the adrenal glands don’t produce enough cortisol, is one of the more significant hormonal causes. Cortisol plays a key role in keeping blood sugar stable, especially during illness, fasting, or physical stress. Without adequate cortisol, your body can’t mount the normal response to prevent glucose from dropping too low. The risk climbs even higher when adrenal insufficiency is paired with growth hormone deficiency. A large cohort study of patients with multiple pituitary hormone deficiencies found that hypoglycemia was highlighted in 31% of sudden, unexpected deaths in that group.
Thyroid disorders and pituitary gland problems can also disrupt glucose regulation, though they tend to cause less dramatic drops on their own.
Liver and Kidney Disease
Your liver is essentially your blood sugar warehouse. It stores glucose and releases it between meals to keep levels steady. When the liver is severely damaged from conditions like cirrhosis, hepatitis, or liver failure, it loses the ability to store and release glucose effectively. This makes low blood sugar episodes more likely, particularly during fasting or overnight.
Chronic kidney disease adds its own layer of risk. The kidneys contribute to glucose production directly, and when they’re impaired, that contribution drops. Kidney disease also changes how your body processes medications, meaning drugs that normally wouldn’t cause low blood sugar may linger in the system longer and push glucose down further. On top of that, people with advanced kidney disease often deal with poor appetite and malnutrition, which compounds the problem.
Reactive Hypoglycemia After Meals
Some people experience low blood sugar not from fasting, but two to five hours after eating. This is called reactive hypoglycemia, and it can be a sign of several things. In some cases, it’s an early indicator of prediabetes. The body overproduces insulin in response to a meal, bringing sugar down too far after the initial spike.
People who’ve had stomach surgery, including weight loss procedures, are particularly prone to a form called alimentary reactive hypoglycemia. Food empties from the stomach into the small intestine too quickly, triggering a flood of insulin. This typically happens within two hours of eating. A similar pattern can occur in people with naturally fast gastric emptying, even without prior surgery, a condition sometimes called Middleton Syndrome.
If your low blood sugar episodes consistently happen a few hours after meals rather than during fasting, reactive hypoglycemia is a likely explanation worth investigating.
Alcohol and Fasting
Alcohol is one of the most overlooked causes of low blood sugar. When you drink, your liver prioritizes breaking down alcohol over its usual job of producing glucose. This suppresses two critical processes: the liver’s ability to make new glucose and its ability to release glucose from stored reserves. Alcohol can also increase insulin secretion and slow glucose absorption from the intestines.
The risk is highest when drinking on an empty stomach or after prolonged fasting, because your glucose reserves are already low. The combination of alcohol and limited food intake can produce dangerously low blood sugar levels, and the symptoms of hypoglycemia (confusion, unsteadiness, slurred speech) are easy to mistake for intoxication, which means the problem often goes unrecognized.
Insulinoma and Other Rare Causes
In rare cases, recurrent low blood sugar points to an insulinoma, a small tumor in the pancreas that produces excess insulin regardless of how much glucose is in the blood. These tumors are uncommon, occurring in roughly 1 to 32 cases per million people per year, but they’re worth considering when someone without diabetes has repeated, unexplained hypoglycemia episodes, especially during fasting.
Doctors diagnose insulinomas by measuring insulin, a related protein called C-peptide, and blood sugar simultaneously. A key finding is abnormally high insulin alongside blood sugar below 55 mg/dL. The vast majority of insulinomas are benign and can be surgically removed.
Other rare causes include large tumors outside the pancreas that produce insulin-like substances, certain autoimmune conditions where the body makes antibodies against insulin or its receptor, and inherited metabolic disorders that typically present in childhood.
How to Recognize the Warning Signs
Low blood sugar produces two distinct waves of symptoms. The first wave is your body’s alarm system: trembling, a pounding heart, sweating, anxiety, hunger, and tingling in the hands or lips. These early signs come from your nervous system responding to the drop in glucose and are your cue to act.
If blood sugar continues to fall, a second wave hits. This time the symptoms come from the brain itself being starved of fuel: confusion, difficulty thinking, weakness, a strange sensation of warmth, and in severe cases, seizures or loss of consciousness. People who experience frequent episodes of low blood sugar can develop what’s called hypoglycemia unawareness, where the early alarm signals become blunted and the first noticeable symptoms are the more dangerous neurological ones.
What to Do During an Episode
The standard approach is the 15-15 rule recommended by the CDC: eat or drink 15 grams of fast-acting carbohydrates (about four glucose tablets, half a cup of juice, or a tablespoon of honey), wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process. Once your levels stabilize, eat a small meal or snack with protein and complex carbohydrates to prevent another drop.
Severe episodes where a person can’t eat or drink safely, or has lost consciousness, require emergency treatment. This is classified as level 3 hypoglycemia regardless of the actual glucose reading, because the person needs someone else’s help to recover.
How Doctors Identify the Cause
Clinicians use a framework called Whipple’s triad to confirm true hypoglycemia: you must have symptoms of low blood sugar, a documented blood glucose below 55 mg/dL at the time of symptoms, and resolution of those symptoms once blood sugar is brought back up. All three criteria need to be met, because many symptoms of hypoglycemia overlap with anxiety, dehydration, and other conditions.
From there, the workup depends on context. If you’re on diabetes medication, the cause is usually straightforward. For people without diabetes, doctors typically check cortisol levels, liver and kidney function, and insulin levels to narrow down the possibilities. Patterns matter too: episodes that happen after fasting point toward different causes than those occurring after meals. Keeping a log of when your symptoms happen, what you’ve eaten, and any medications you’ve taken gives your doctor the clearest picture of what’s going on.