Blood sugar drops when your body uses glucose faster than it can replace it, or when too much insulin pushes glucose out of your bloodstream and into cells. A reading below 70 mg/dL is considered low, and anything below 54 mg/dL is classified as severely low. The causes range from everyday habits like skipping meals and exercising hard to medications, alcohol, and rare medical conditions.
How Your Body Regulates Blood Sugar
Understanding what makes blood sugar drop starts with how your body manages glucose in the first place. After you eat, carbohydrates break down into glucose, which enters your bloodstream. In response, your pancreas releases insulin. Insulin works by signaling your cells to open special glucose channels on their surfaces. These channels, normally stored inside cells, physically move to the cell wall so glucose can pass through. Once glucose enters your muscle and fat cells, blood sugar levels fall.
When blood sugar gets too low, your body has a backup system. Your pancreas releases glucagon, a hormone that tells your liver to convert stored glycogen back into glucose and release it into the blood. Stress hormones like adrenaline and cortisol also kick in, typically when glucose drops into the range of 65 to 70 mg/dL. This counter-regulatory response is why most healthy people rarely experience dangerously low blood sugar. Problems arise when something disrupts either side of this equation: too much glucose leaving the blood, or not enough being released back in.
Skipping or Delaying Meals
Your liver stores enough glycogen to maintain blood sugar for several hours between meals, but those reserves aren’t unlimited. When you skip a meal or go unusually long without eating, your liver’s glycogen supply starts running low. If you’re also physically active or under stress during that window, glucose gets used up even faster. This is one of the most common and straightforward reasons blood sugar drops in otherwise healthy people.
The timing matters too. Going without dinner, for example, creates a long overnight fast that can push blood sugar lower by morning. People who eat irregularly or follow very restrictive diets are more prone to these dips, especially if their meals are small when they do eat.
Exercise and Physical Activity
Physical activity pulls glucose out of your bloodstream to fuel working muscles. During exercise, your muscles can absorb glucose even without insulin, which means blood sugar can fall quickly during intense or prolonged workouts. But what surprises many people is how long the effect lasts. According to the American Diabetes Association, physical activity can lower blood sugar for up to 24 hours after a workout by increasing your body’s sensitivity to insulin.
This extended window means a hard afternoon workout could lead to a blood sugar drop during sleep that night. The risk is higher if you exercised without eating enough beforehand, or if you take insulin or other blood sugar-lowering medications. Even people without diabetes can feel shaky or lightheaded after unusually strenuous activity if they haven’t fueled properly.
Reactive Hypoglycemia After Eating
It sounds counterintuitive, but eating can actually cause blood sugar to drop, sometimes significantly. Reactive hypoglycemia occurs when blood sugar falls within four hours after a meal. The typical pattern involves eating a large amount of refined carbohydrates, which causes a rapid spike in blood sugar followed by an oversized insulin response. That excess insulin then drives blood sugar below where it started.
In people without diabetes, the exact cause often isn’t clear, though it tends to correlate with what and when a person eats. High-sugar, low-fiber meals are the most common trigger. People who have had gastric bypass or other bariatric surgery are particularly prone to reactive hypoglycemia because food moves through their digestive system faster, causing a more dramatic glucose spike and subsequent crash. Certain inherited metabolic conditions and, rarely, tumors that produce insulin can also cause post-meal drops.
How Alcohol Blocks Glucose Production
Alcohol is one of the most underappreciated causes of low blood sugar. When you drink, your liver prioritizes breaking down alcohol over its other jobs, including producing new glucose. Normally, when blood sugar starts to fall, your liver manufactures glucose through a process called gluconeogenesis. Alcohol directly disrupts this process by changing the chemical environment inside liver cells, essentially blocking the conversion of raw materials into usable glucose.
This means your liver can’t respond to falling blood sugar the way it normally would. The risk is highest when you drink on an empty stomach or drink heavily without eating, because your liver’s glycogen stores may already be low. The drop can happen hours after your last drink, which is why nocturnal hypoglycemia is a known risk after evening alcohol consumption. This isn’t limited to people with diabetes; anyone who drinks enough on an empty stomach can experience it.
Medications That Lower Blood Sugar
Diabetes medications, particularly insulin and drugs that stimulate insulin release, are the most common pharmaceutical cause of low blood sugar. Taking too high a dose, taking your usual dose but eating less than normal, or combining medication with heavy exercise can all tip the balance.
Several non-diabetes medications can also cause blood sugar drops. These include certain beta-blockers used for blood pressure and heart conditions, some antibiotics in the fluoroquinolone family, the anti-malaria drug quinine, and certain heart rhythm medications. Beta-blockers pose a double risk because they can also mask the early warning signs of low blood sugar, like a racing heart, making it harder to recognize a drop before it becomes severe. If you take any of these medications and notice symptoms of low blood sugar, it’s worth discussing with your prescriber.
Overnight Blood Sugar Drops
Blood sugar can fall during sleep for several reasons, and the tricky part is you may not wake up to notice. According to Johns Hopkins Medicine, nocturnal hypoglycemia is more likely in people who skip dinner, exercise before bedtime, drink alcohol in the evening, or have an active infection. Certain types of insulin that peak six to eight hours after injection are a particular risk when taken at dinner, since their strongest effect hits in the middle of the night.
Signs that your blood sugar dropped overnight include waking up with a headache, feeling unusually tired despite a full night’s sleep, or finding damp sheets from sweating. Some people experience restless sleep or nightmares without realizing the cause. If you use a continuous glucose monitor, overnight data can reveal dips you’d otherwise miss entirely.
Rare but Serious Causes
In uncommon cases, persistent low blood sugar points to an underlying medical condition. Insulinomas are small tumors of the pancreas that produce excess insulin regardless of what your blood sugar is doing. They’re diagnosed using a set of criteria known as Whipple’s triad: symptoms of low blood sugar, a confirmed low reading at the time of symptoms, and relief of symptoms when glucose is given. During diagnostic testing, people with insulinomas typically show blood sugar levels below 40 mg/dL alongside inappropriately high insulin levels. These tumors are usually benign and treatable with surgery.
Adrenal insufficiency, severe liver disease, and certain kidney conditions can also impair your body’s ability to maintain blood sugar. These are far less common than dietary or medication-related causes, but they’re worth investigating if you experience repeated unexplained episodes of low blood sugar.
Recognizing and Treating a Drop
The early symptoms of falling blood sugar include shakiness, sweating, a rapid heartbeat, irritability, and sudden hunger. As blood sugar falls further, you may experience confusion, blurred vision, difficulty speaking, or trouble concentrating. Severe drops below 54 mg/dL can cause seizures or loss of consciousness.
The standard approach for treating a mild to moderate drop is called the 15-15 rule: consume 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat. Good options for those 15 grams include half a cup of juice or regular soda, one tablespoon of honey or sugar, or three to four glucose tablets. Once your blood sugar is back in a normal range, follow up with a balanced snack or small meal that includes protein to keep it stable. Young children typically need less than 15 grams per dose.
If someone is unconscious or unable to swallow safely, they need emergency glucagon, which comes in injectable and nasal spray forms, and immediate medical attention.