Low blood sugar, or hypoglycemia, happens when your blood glucose drops below about 70 mg/dL. If you don’t have diabetes, experiencing low blood sugar can be confusing and even alarming. The causes range from something as simple as skipping a meal or drinking alcohol to less common conditions involving your hormones, medications, or rarely, a tumor on your pancreas.
What Low Blood Sugar Feels Like
The symptoms tend to come on quickly: shakiness, sweating, a racing heartbeat, irritability, and sudden hunger. As blood sugar drops further, you might feel dizzy, confused, or have trouble concentrating. In severe cases, you could faint or have a seizure. These symptoms happen because your brain depends on a steady supply of glucose to function, and it reacts fast when supply runs low.
Doctors confirm a true hypoglycemic disorder using three criteria known as Whipple’s triad: you have symptoms consistent with low blood sugar, a lab test shows your glucose is genuinely low at the time of those symptoms, and the symptoms go away once your blood sugar comes back up. This matters because many of these symptoms overlap with anxiety, dehydration, or other conditions. If your symptoms consistently resolve after eating something sugary, that’s a strong clue the problem is your blood sugar.
Blood Sugar Drops After Eating
One of the most common patterns in people without diabetes is reactive hypoglycemia, where blood sugar drops within four hours after a meal. You eat, your body releases insulin to process the glucose, but for some reason it overshoots, pulling your blood sugar too low. This often happens after meals heavy in refined carbohydrates or sugar, which cause a rapid spike followed by an exaggerated insulin response.
In many cases, the exact cause of reactive hypoglycemia isn’t clear. But certain factors make it more likely. People who’ve had gastric bypass or other bariatric surgery are particularly prone to it because food moves through the digestive system faster, triggering a more intense insulin release. Rare inherited metabolic conditions can also play a role.
Alcohol and Skipping Meals
Your liver acts as a glucose reservoir, steadily releasing stored sugar into your bloodstream between meals to keep levels stable. It does this through a process called gluconeogenesis, essentially manufacturing new glucose from raw materials. Alcohol directly interferes with this process. Research published in the American Journal of Physiology found that alcohol consumption reduced the liver’s glucose production by about 45% over the five hours after drinking, while also cutting the availability of the building blocks the liver needs to make glucose by 61%.
This is why drinking on an empty stomach is a recipe for low blood sugar. Your liver is already working to keep glucose steady because you haven’t eaten, and alcohol effectively shuts down its main backup system. The combination of fasting and alcohol is one of the most common causes of hypoglycemia in people who don’t take diabetes medications. Even moderate drinking with a light meal can cause a noticeable dip, especially if you’re not eating enough carbohydrates alongside the alcohol.
Medications That Lower Blood Sugar
Several medications can cause low blood sugar, and not all of them are diabetes drugs. Certain antibiotics, including some fluoroquinolones and the antimalarial drug quinine, have been linked to hypoglycemia. Some heart rhythm medications and even the common pain reliever indomethacin can lower blood sugar. Beta-blockers, used for high blood pressure and anxiety, are another culprit, and they can also mask the typical warning symptoms like a racing heart, making it harder to notice the drop.
If you take diabetes medications, the risk is more straightforward. Sulfonylureas and similar drugs work by stimulating your pancreas to produce more insulin, which can overshoot if you skip a meal, eat less than usual, or exercise more than expected. If you’ve recently started a new medication or changed your dose and notice symptoms like shakiness, sweating, or sudden confusion, the medication is worth investigating as a possible cause.
Hormonal Causes
Your body relies on several hormones to keep blood sugar from falling too low. Cortisol, produced by the adrenal glands, plays a key role in helping your body convert stored energy into usable glucose. When the adrenal glands don’t produce enough cortisol, a condition called adrenal insufficiency or Addison’s disease, low blood sugar is one of the early symptoms. People with this condition may also experience fatigue, weight loss, darkened skin, and low blood pressure.
Problems with the pituitary gland can have a similar effect. The pituitary controls many of the body’s hormone-producing glands, including the adrenals, and deficiencies in the hormones it produces can impair your body’s ability to maintain stable blood sugar. These hormonal causes are less common, but they’re worth considering if you have persistent or unexplained episodes of low blood sugar alongside other symptoms like chronic fatigue or unintentional weight loss.
Insulinomas and Other Rare Causes
An insulinoma is a small tumor on the pancreas that produces excess insulin, flooding the body with more than it needs and driving blood sugar dangerously low. These tumors are rare, but they cause a distinctive pattern: repeated episodes of low blood sugar that don’t have an obvious trigger, often occurring during fasting or between meals.
Diagnosis typically involves a supervised fasting test lasting up to 72 hours, during which doctors monitor whether your blood sugar drops and measure insulin levels at the same time. In a healthy person, insulin production slows down as blood sugar falls. In someone with an insulinoma, insulin stays inappropriately high even as glucose plummets. If the fasting test points to an insulinoma, imaging with CT, MRI, or endoscopic ultrasound helps locate the tumor. The vast majority of insulinomas are benign and can be surgically removed.
Exercise-Related Blood Sugar Drops
Intense or prolonged exercise burns through your glucose stores, which is why you might feel shaky or lightheaded during or after a hard workout. But the effect doesn’t always stop when the exercise does. Physical activity increases your body’s sensitivity to insulin for several hours afterward, meaning your cells continue pulling glucose out of the bloodstream more efficiently than usual. This can lead to a delayed drop in blood sugar that shows up hours later, sometimes even during sleep after an evening workout.
For most people without diabetes, this effect is mild and easily corrected by eating a balanced meal or snack after exercising. But if you’re combining intense exercise with restricted eating, fasting, or alcohol, the risk of a meaningful blood sugar drop increases substantially.
What to Do When Blood Sugar Drops
The standard approach is called the 15-15 rule: 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 quick carbohydrates include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
If you’re having repeated episodes of low blood sugar and you don’t have diabetes, that’s worth tracking carefully. Note when the episodes happen (fasting, after meals, after exercise, during the night), what you ate beforehand, and what made the symptoms go away. This pattern is often the most useful information in figuring out the underlying cause. Frequent episodes that occur during fasting, that wake you up at night, or that happen without an obvious dietary trigger are the ones that most warrant further investigation.