Persistent low blood sugar that won’t come up, or keeps dropping after you raise it, usually means something is actively pulling glucose out of your bloodstream or blocking your body’s ability to produce it. A normal fasting blood sugar sits between 70 and 100 mg/dL. Below 70 mg/dL is considered low (hypoglycemia), and below 54 mg/dL is serious enough to cause confusion, vision changes, or loss of consciousness.
What Happens When Blood Sugar Drops
Your body has a layered defense system to keep blood sugar from falling too far. When glucose starts to dip, your pancreas releases a hormone called glucagon, which tells your liver to dump stored sugar into your bloodstream. If that’s not enough, your adrenal glands release stress hormones that trigger your liver to make new glucose from scratch (a process called gluconeogenesis) and slow down how fast your muscles burn through what’s available. These defenses work in sequence, each one kicking in as levels continue to fall.
When blood sugar won’t come up despite eating, it means one or more of those defenses has failed, or something is overwhelming them. The causes range from simple and fixable to medical conditions that need treatment.
The Most Common Everyday Causes
Before considering medical explanations, it’s worth ruling out the most frequent triggers. Not eating enough is the obvious one, but how you eat matters too. If you go long stretches without food, your liver’s stored sugar (glycogen) gradually depletes. Once those stores run out, your body relies entirely on making glucose from protein and fat, which is slower and less efficient. Skipping meals, fasting, or eating very low-carb without adjusting can leave your system unable to keep up.
Intense or prolonged exercise is another common culprit. Your muscles can burn through glucose faster than your liver can replace it, especially if you haven’t eaten recently. This can drop blood sugar for hours after a workout.
Alcohol and Low Blood Sugar
Alcohol is one of the most underrecognized causes of stubborn low blood sugar. When your liver processes alcohol, the chemical reaction shifts the balance of a key molecule (NAD) that your liver needs to manufacture new glucose. This essentially blocks gluconeogenesis for as long as alcohol is being metabolized. If you’ve been drinking on an empty stomach or after a period of not eating much, your liver can’t make glucose and its stored supply may already be low. The result is blood sugar that drops and stays down, sometimes for hours. This effect is more dangerous than most people realize, especially because the symptoms of low blood sugar (dizziness, confusion, slurred speech) can look a lot like intoxication.
Medications That Lower Blood Sugar
If you take diabetes medication, especially insulin or drugs that stimulate insulin release, too much medication relative to your food intake is the single most common reason blood sugar won’t come up. This can happen when you take your usual dose but eat less than normal, exercise more, or take your medication at the wrong time.
Several non-diabetes medications also lower blood sugar as a side effect. Beta-blockers used for blood pressure and heart conditions can suppress some of the warning signals your body sends during low blood sugar, making it harder to detect and respond to drops. Certain antibiotics, particularly fluoroquinolone antibiotics like levofloxacin and gatifloxacin, have also been linked to unexpected glucose drops. If your blood sugar problems started around the same time as a new prescription, that connection is worth investigating.
Reactive Hypoglycemia After Eating
Some people experience blood sugar that spikes after a meal, then crashes hard one to three hours later. This is called reactive hypoglycemia. What happens is the initial spike triggers your pancreas to release a large burst of insulin, but the insulin keeps working after the sugar from your meal has been absorbed, pulling your blood sugar down too far. Meals heavy in refined sugars and starches are the most common trigger.
This pattern is especially common after gastric bypass or other stomach surgeries, where food moves into the small intestine faster than normal. The rapid absorption of sugar causes an exaggerated insulin response. In this context it’s called dumping syndrome, and it can make blood sugar extremely difficult to stabilize after meals.
Hormonal Causes
Cortisol, the hormone your adrenal glands produce, plays a central role in keeping blood sugar stable. It promotes glucose production in the liver and slows down how quickly your tissues absorb sugar from the blood. When cortisol is deficient, as in adrenal insufficiency (sometimes called Addison’s disease), the effects on blood sugar are significant. Without adequate cortisol, your body becomes more sensitive to insulin, meaning tissues pull sugar from the bloodstream faster than normal. At the same time, your liver produces less glucose. The combination makes blood sugar stubbornly low, particularly during illness, stress, or fasting, when cortisol would normally rise to compensate.
Growth hormone deficiency has a similar, though typically milder, effect. Both cortisol and growth hormone serve as longer-acting safety nets that prevent blood sugar from falling during sustained periods without food. When either is missing, fasting tolerance drops sharply.
Liver and Pancreatic Problems
Your liver is essentially a glucose factory. It stores sugar after meals and releases it between meals, and it can manufacture new glucose when stores run low. Severe liver disease, whether from cirrhosis, acute liver failure, or advanced hepatitis, impairs all of these functions. The liver can’t store enough glycogen, can’t convert other molecules into glucose efficiently, and may not properly regulate insulin and glucagon. People with advanced liver disease often struggle with blood sugar that drops unpredictably and resists correction.
On the pancreatic side, a rare but important cause is an insulinoma, a small tumor in the pancreas that continuously secretes insulin regardless of how low blood sugar gets. The hallmark is fasting blood sugar dropping below 50 mg/dL while insulin levels remain inappropriately high. These tumors are almost always benign and can be surgically removed, but they cause persistent, hard-to-explain low blood sugar that characteristically worsens with fasting.
In very rare cases, large non-pancreatic tumors (often found in the chest or abdomen) can produce a substance similar to insulin called IGF-2. This mimics insulin’s effects throughout the body: driving glucose into cells, shutting down liver glucose production, and suppressing the hormones that would normally raise blood sugar. The result is severe, refractory hypoglycemia that doesn’t respond well to standard treatment.
Why Repeated Low Episodes Make the Problem Worse
If you have diabetes and experience frequent low blood sugar, your body can lose its ability to detect and respond to drops. This creates a dangerous cycle. Normally, when blood sugar falls, your body releases adrenaline, which produces noticeable warning symptoms: shaking, sweating, a racing heart. But repeated episodes of low blood sugar gradually reset the threshold at which these alarms fire, pushing it lower and lower. Eventually, you may not feel any symptoms until your blood sugar is dangerously low.
This condition, called hypoglycemia unawareness, also blunts the glucagon and adrenaline responses that would normally raise your blood sugar back up. So not only do you miss the warning signs, but your body’s automatic correction system is weakened. The key to reversing this cycle is strictly avoiding low blood sugar for several weeks, which allows the body’s warning thresholds to reset back to normal levels.
What to Do When Blood Sugar Won’t Come Up
For an acute episode, 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 recheck your blood sugar. If it’s still below 70 mg/dL, repeat. Keep repeating until your levels return to your target range. Good sources of 15 grams of fast-acting carbs include four glucose tablets, four ounces of juice, or a tablespoon of honey.
If the 15-15 rule isn’t working after two or three rounds, or if symptoms are worsening (confusion, inability to swallow safely, loss of consciousness), that’s a medical emergency. Glucagon kits, available by prescription, can be administered by another person when someone is too impaired to eat.
For blood sugar that keeps dropping chronically, the fix depends entirely on the cause. If medication is responsible, dose adjustments or timing changes often solve the problem. If reactive hypoglycemia is the pattern, smaller and more frequent meals with protein and fat (which slow sugar absorption) and fewer refined carbohydrates can flatten the spike-and-crash cycle. If none of the obvious explanations fit, a medical workup is warranted. Doctors look for what’s called Whipple’s triad: documented low blood sugar, symptoms that match hypoglycemia, and resolution of those symptoms once blood sugar is corrected. Meeting all three criteria is the starting point for investigating hormonal, liver, or pancreatic causes.