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. For most people, blood sugar stays between 70 and 100 mg/dL through a tightly coordinated system of hormones and organ functions. When any part of that system misfires, whether from medication, missed meals, hormonal problems, or intense exercise, glucose can fall below 70 mg/dL and trigger symptoms ranging from shakiness to confusion.
How Your Body Normally Prevents a Drop
Your liver is the central player in keeping blood sugar stable. It stores glucose in a compact form called glycogen and releases it back into the bloodstream whenever levels start to dip. During a short fast, like the hours between meals, your liver breaks down glycogen to supply a steady stream of glucose. If fasting stretches longer (overnight, for example), glycogen stores run low, and the liver switches to manufacturing fresh glucose from other raw materials like amino acids and fats.
Two hormones from the pancreas orchestrate this process. Insulin, released after you eat, signals cells to absorb glucose and tells the liver to stop producing it. Glucagon does the opposite: when blood sugar falls, it tells the liver to break down glycogen and ramp up new glucose production. A drop in blood sugar typically means either too much insulin is circulating, the glucagon signal is weak, the liver can’t keep up with demand, or some combination of the three.
Medication-Related Drops
The most common cause of significant low blood sugar is diabetes medication. Injected insulin directly lowers glucose, so taking too much, timing a dose incorrectly, or eating less than expected after a dose can send blood sugar plummeting. The risk is straightforward: more insulin in the bloodstream than the available glucose can match.
Certain oral diabetes medications called sulfonylureas work by forcing the pancreas to release insulin regardless of what your blood sugar is doing at that moment. They bind to receptors on insulin-producing cells, trigger calcium to flow in, and cause stored insulin to be dumped into the bloodstream. Because this release isn’t tied to your actual glucose level, these drugs can push blood sugar too low, especially if you skip a meal or exercise more than usual. Sulfonylureas can also suppress glucagon, reducing your liver’s ability to compensate.
Reactive Hypoglycemia After Meals
Some people experience blood sugar drops within four hours of eating, a pattern called reactive hypoglycemia. This is common in people without diabetes and often catches them off guard because it happens after a meal, not during fasting.
The exact mechanism isn’t always clear, but the general pattern involves an exaggerated insulin response. You eat a meal (especially one high in refined carbohydrates), blood sugar spikes, and your pancreas overshoots with too much insulin. The excess insulin drives glucose into cells so aggressively that blood sugar falls below comfortable levels a couple of hours later. You feel shaky, hungry, or lightheaded right around mid-morning or mid-afternoon.
Other triggers for post-meal drops include alcohol, which impairs the liver’s ability to release glucose, and prior gastric bypass surgery, which changes how quickly food reaches the small intestine and can cause rapid, exaggerated sugar absorption followed by an insulin surge. Rare inherited metabolic conditions and certain tumors can also cause reactive drops.
Hormonal Causes Beyond Insulin
Insulin and glucagon aren’t the only hormones involved. Your body has several backup systems to prevent blood sugar from falling too low, and problems with any of them can leave you vulnerable.
Growth hormone acts as a safety net against drops. It stimulates the liver to produce glucose, reduces how much glucose muscles absorb, and helps counteract insulin’s effects. People with growth hormone deficiency have a higher rate of spontaneous low blood sugar episodes. In children, this deficiency can cause recurring drops during the early years before the issue is identified.
Cortisol, produced by the adrenal glands, plays a similar protective role. It helps mobilize glucose during stress and fasting. When the adrenal glands can’t produce enough cortisol (a condition called adrenal insufficiency), the body loses one of its key defenses against dropping blood sugar, particularly during illness, physical stress, or prolonged gaps between meals.
Exercise and Delayed Drops
Physical activity burns through glucose quickly, which is why blood sugar can fall during a workout. But the more surprising risk is what happens afterward. Exercise increases your body’s sensitivity to insulin for many hours after you stop, and there’s evidence of a second peak in insulin sensitivity that can occur well into the evening or overnight. For people with type 1 diabetes, this means the window of risk for a low blood sugar episode extends into the nighttime hours, sometimes catching people while they sleep.
Even for people without diabetes, a hard workout combined with insufficient food can result in a noticeable drop. The combination of depleted glycogen stores and heightened insulin sensitivity makes the post-exercise window a vulnerable time, especially if you skip your post-workout meal or snack.
Skipping Meals and Alcohol
Your liver’s glycogen stores are limited. After roughly 12 to 18 hours of fasting, they begin to run low, and the liver must work harder to manufacture glucose from scratch. Skipping meals, particularly breakfast after an overnight fast, forces this system to compensate. For most healthy people, the backup mechanisms hold. But if you combine a skipped meal with another risk factor (alcohol, exercise, a hormonal deficiency), the system can be overwhelmed.
Alcohol deserves special mention because it directly blocks the liver’s ability to produce new glucose. When you drink on an empty stomach or after exercise, your liver is busy processing alcohol and can’t respond to falling blood sugar the way it normally would. This is why low blood sugar from alcohol often strikes hours after drinking, not immediately.
What a Blood Sugar Drop Feels Like
The symptoms come in two waves, driven by different mechanisms. The first wave happens because your body releases adrenaline to try to push blood sugar back up. This causes sweating, trembling, a racing heartbeat, anxiety, and intense hunger. These warning signs typically appear when blood sugar dips below 70 mg/dL, and they serve an important purpose: they prompt you to eat.
If blood sugar continues to fall below about 50 mg/dL, the brain itself starts running short on fuel. At this point, symptoms shift to confusion, difficulty concentrating, slurred speech, blurred vision, and in severe cases, seizures or loss of consciousness. Unlike the adrenaline-driven symptoms, these brain-related effects indicate a more serious situation that requires immediate attention.
People who experience frequent low blood sugar episodes can lose the adrenaline warning signs over time. Their body stops sounding the alarm at 70 mg/dL, so the first noticeable symptoms are the more dangerous brain-related ones. This is called hypoglycemia unawareness and is most common in people with long-standing type 1 diabetes.
How to Bring Blood Sugar Back Up
The CDC recommends the 15-15 rule: eat 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck your blood sugar. If it’s still below 70 mg/dL, repeat the process until it reaches your target range. Good sources of 15 grams include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. Young children, especially infants and toddlers, need less than 15 grams.
The key is choosing simple carbohydrates that absorb quickly. Foods with fat or protein (like a candy bar or peanut butter crackers) slow digestion and delay the recovery. Once blood sugar stabilizes, eating a balanced snack or meal helps prevent it from dropping again, especially if the next meal is more than an hour away.