Persistently low blood sugar, called hypoglycemia, happens when your blood glucose drops below 70 mg/dL (3.9 mmol/L). If this keeps happening to you, something is driving your body to either use glucose too quickly, produce too much insulin, or fail to release stored glucose when it needs to. The cause could be as straightforward as your eating pattern or as specific as a hormonal imbalance, and figuring out which one matters for getting it to stop.
What Low Blood Sugar Feels Like
Hypoglycemia produces two distinct waves of symptoms, and recognizing them helps you understand how far your glucose has dropped. The first set comes from your body’s stress response: sweating, shakiness, a pounding heart, hunger, and anxiety. These kick in because your nervous system detects falling glucose and floods your body with adrenaline to try to correct it.
If glucose keeps dropping, a second set of symptoms appears because your brain itself is running low on fuel. These include difficulty concentrating, confusion, slurred speech, blurred vision, and in severe cases, loss of consciousness. The brain uses more glucose than any other organ, so it’s the first to suffer when supply runs short. If you’re regularly experiencing that foggy, confused feeling between meals or after waking up, your blood sugar may be dipping lower than the early warning signs alone would suggest.
It’s worth noting that some young women can have fasting glucose levels between 50 and 70 mg/dL without symptoms, which is considered normal for them. The key diagnostic standard, known as Whipple’s Triad, requires three things to confirm a true problem: a measured low glucose level, symptoms consistent with low glucose, and improvement of those symptoms once glucose comes back up. If you feel terrible but your glucose reads normal, something else may be going on.
Reactive Hypoglycemia: The Most Common Culprit
The most frequent reason for recurring low blood sugar in people without diabetes is reactive hypoglycemia, where glucose crashes one to three hours after eating. The pattern usually looks like this: you eat a meal heavy in carbohydrates or sugar, your blood sugar spikes, your pancreas overreacts by releasing too much insulin, and then your glucose plummets below where it started.
The underlying mechanism involves your stomach emptying food into the small intestine faster than normal, which triggers a rapid glucose spike. That spike causes gut hormones called incretins to surge, which in turn amplify insulin release well beyond what was needed. The result is a sharp overcorrection. This pattern can also be an early sign of insulin resistance. One of the first changes as the body moves toward type 2 diabetes is a delayed initial insulin response, followed by an exaggerated second wave of insulin that overshoots and causes a glucose drop.
If your low blood sugar episodes consistently happen in the window after meals rather than first thing in the morning, reactive hypoglycemia is the most likely explanation.
Low Blood Sugar After Gastric Surgery
If you’ve had gastric bypass or another weight-loss surgery, recurring low blood sugar may be a consequence of how your digestive system now handles food. About 1 in 4 people who’ve had gastric bypass experience what’s called late dumping syndrome, where food moves too quickly from the smaller stomach pouch into the intestine. The rapid absorption of sugar triggers a massive insulin surge, and blood glucose crashes one to three hours later.
Symptoms can be intense: heart palpitations, sweating, confusion, tremors, extreme fatigue, and even fainting. These episodes are most likely after meals high in starches or sugars, including fructose and table sugar. If you had bariatric surgery months or even years ago and are now experiencing these drops, this is a well-documented complication worth discussing with your surgical team.
Conditions That Cause Fasting Hypoglycemia
If your blood sugar drops during long gaps between meals or overnight while you sleep, the cause is different from reactive hypoglycemia. Fasting hypoglycemia points to a problem with how your body maintains glucose when you’re not eating, and several conditions can be responsible.
Insulinoma
An insulinoma is a rare tumor in the pancreas that continuously releases insulin regardless of your glucose level. Most people with an insulinoma notice their worst episodes in the morning after an overnight fast, because the tumor kept pumping insulin all night while no food was coming in. About 5% to 10% of insulinoma cases are linked to an inherited condition called MEN1, which causes tumors across multiple hormone-producing glands.
To diagnose an insulinoma, doctors use a supervised fasting test. You fast at home for 8 to 12 hours, then continue fasting in a hospital where your glucose is checked every four hours, then hourly once it dips below 60 mg/dL. The fast ends when glucose drops below 45 mg/dL or severe symptoms develop. Blood tests at that point can reveal whether your insulin levels are inappropriately high for such low glucose, which is the hallmark of an insulinoma.
Adrenal and Hormonal Problems
Your adrenal glands produce cortisol, which plays a direct role in keeping blood sugar stable between meals by signaling the liver to release stored glucose. If your adrenals aren’t producing enough cortisol (a condition called adrenal insufficiency), your liver doesn’t get that signal, and blood sugar can drift dangerously low during fasting or stress. Growth hormone deficiency can cause a similar problem, since growth hormone also helps maintain glucose levels between meals.
Liver Disease
Your liver is the main glucose warehouse. It stores glucose after meals and releases it between meals to keep blood sugar steady. Severe liver disease can impair this storage-and-release system, leaving you without a buffer when you haven’t eaten recently.
Non-Islet Cell Tumors
In rare cases, large tumors outside the pancreas (often in the chest or abdomen) can cause severe hypoglycemia by producing a substance that mimics insulin’s effects. These tumors secrete an abnormal form of a growth factor that forces muscles to absorb glucose at a high rate while simultaneously blocking the liver from releasing its glucose stores. It also suppresses other hormones that would normally raise blood sugar, like glucagon and growth hormone. The result is profound and persistent low glucose that can be difficult to manage until the tumor is treated.
Medications That Lower Blood Sugar
Several medications prescribed for conditions other than diabetes can cause low blood sugar as a side effect. Common culprits include beta-blockers used for blood pressure and heart conditions, certain antibiotics in the fluoroquinolone family, the anti-malarial drug quinine, and some heart rhythm medications. Beta-blockers are particularly tricky because they can also mask the early warning symptoms of low blood sugar, like a racing heart, so you may not realize your glucose is dropping until confusion or dizziness sets in.
If your episodes of low blood sugar started around the same time as a new medication, that timing is worth flagging. Alcohol can also cause hypoglycemia, especially if you drink without eating, because it interferes with your liver’s ability to produce and release glucose.
How to Manage Recurring Low Blood Sugar
The right long-term strategy depends on the cause, but the dietary approach is the same regardless: keep your blood sugar from spiking so it doesn’t crash afterward. Eating small meals every three hours is one of the most effective changes you can make. Each meal should pair carbohydrates with protein or fat, which slows digestion and produces a gentler, more sustained rise in blood sugar. Think chicken with rice instead of rice alone, or cheese with crackers instead of crackers by themselves.
Choosing low-glycemic foods makes a significant difference. Foods high in fiber, like whole grains, legumes, and most vegetables, are absorbed more slowly and help keep glucose stable. Meanwhile, high-sugar foods like candy, honey, jam, and sugary drinks cause the rapid spikes that trigger overcorrection. Keeping carbohydrate portions moderate at each meal, rather than eating one large carb-heavy plate, also helps prevent the insulin overshoot that leads to reactive drops.
When you feel symptoms coming on or test your blood sugar below 70 mg/dL, the immediate fix is about 15 grams of fast-acting carbohydrate: a few glucose tablets, half a cup of juice, or a tablespoon of honey. Once symptoms improve, follow up with a small snack that includes protein and a slow-digesting carbohydrate to keep your levels from dropping again. This two-step approach, a quick fix followed by sustained fuel, prevents the rebound crash that often follows treating a low with sugar alone.
Getting the Right Diagnosis
If your blood sugar is dropping frequently, tracking when episodes happen relative to meals is one of the most useful things you can do before a medical appointment. Episodes that cluster one to three hours after eating point toward reactive hypoglycemia. Episodes that happen after overnight fasts or long gaps without food suggest a fasting cause that may need further investigation, including blood work to check insulin levels, cortisol, and liver function.
A continuous glucose monitor, which tracks your blood sugar around the clock, can reveal patterns you’d miss with occasional finger sticks. It can show whether your glucose is dipping at night while you sleep, how sharply it spikes and crashes after meals, and whether certain foods or activities are consistent triggers. This data transforms a vague complaint of “my blood sugar is always low” into a clear pattern that points toward a specific cause.