Glucagon is a hormone that raises your blood sugar. When glucose levels drop, your pancreas releases glucagon to signal the liver to push stored sugar back into your bloodstream. It works as the direct counterpart to insulin: insulin lowers blood sugar after you eat, and glucagon raises it when levels fall too low. Together, these two hormones keep your blood sugar in a narrow, healthy range throughout the day.
How Glucagon Raises Blood Sugar
Glucagon’s primary target is the liver, where it triggers two distinct processes. The first is glycogenolysis, which is essentially the breakdown of glycogen, a stored form of glucose your liver keeps on hand. Glucagon activates a chain of enzymes that unlocks these glycogen reserves and releases glucose directly into the blood. This is the fastest way your body restores blood sugar, and it kicks in within minutes.
The second process is gluconeogenesis, where the liver manufactures brand-new glucose from non-sugar building blocks like amino acids and certain fats. This pathway becomes more important during extended fasting, when glycogen stores start to run low. At the same time, glucagon shuts down the opposing processes: it inhibits glycogen production and slows down glycolysis (the burning of glucose for energy inside liver cells). The net effect is that your liver shifts entirely into glucose-exporting mode.
What Triggers Glucagon Release
Glucagon is produced by alpha cells in the pancreas. The strongest trigger for its release is a drop in blood sugar. When circulating glucose falls, alpha cells detect the change directly and begin secreting glucagon. Your nervous system also plays a role, with signals from the brain amplifying the response during stress or exercise.
Just as important as what triggers glucagon is what suppresses it. After a meal, when blood sugar rises, neighboring beta cells in the pancreas release insulin along with other signaling molecules like zinc and GABA. These paracrine signals act locally on the alpha cells and dial glucagon secretion down. Research shows that glucose itself is the dominant suppressor, capable of reducing glucagon output by about 70% even when insulin levels are held constant. This layered control system, part direct glucose sensing and part signals from neighboring cells, keeps insulin and glucagon in a precise, shifting ratio that matches your body’s needs moment to moment.
The Insulin-Glucagon Balance
In a healthy body, insulin and glucagon move in opposite directions. Immediately after a meal, insulin rises and glucagon falls. During an overnight fast or between meals, insulin drops and glucagon rises. It’s not just the absolute levels of each hormone that matter but their ratio to each other. A higher glucagon-to-insulin ratio tells the liver to release glucose; a lower ratio tells it to store glucose.
This balance breaks down in diabetes. People with type 1 and type 2 diabetes often have elevated glucagon levels or an abnormally high glucagon-to-insulin ratio, which drives the liver to keep pumping out glucose even when blood sugar is already too high. This is one reason blood sugar can be so difficult to control in diabetes: it’s not only about insufficient insulin but also about excess glucagon working against it.
Effects Beyond Blood Sugar
Glucagon does more than manage glucose. It has measurable effects on the heart, increasing both the force and rate of contraction. These effects operate through glucagon’s own dedicated receptor on heart muscle cells, independent of the adrenaline system. In dogs, glucagon infused directly into the heart’s pacemaker region speeds up the heart rate and increases conduction speed. Most human studies confirm similar effects on heart rate and contractile strength.
Glucagon also relaxes smooth muscle throughout the body, particularly in the gastrointestinal tract. This is why it’s sometimes used as a diagnostic tool during imaging: by temporarily relaxing the stomach and intestinal walls, it produces clearer X-ray and endoscopy images. It can also reduce peripheral arterial resistance, which lowers blood pressure, a side effect that shows up in clinical trials.
Emergency Use for Severe Low Blood Sugar
The most well-known medical use of glucagon is as an emergency treatment for severe hypoglycemia, the kind of dangerously low blood sugar that can cause confusion, seizures, or loss of consciousness in people taking insulin. When someone can’t eat or drink to bring their sugar back up, an injection or nasal spray of glucagon can do the job from the outside.
After injection, blood sugar begins rising within about 10 minutes. Peak glucose levels occur 30 to 45 minutes after a subcutaneous or intramuscular dose, and 5 to 20 minutes after an intravenous dose. The effect lasts roughly 60 to 90 minutes before blood sugar starts drifting back down, which is why eating as soon as possible afterward is important. Blood sugar typically returns to baseline within one to two hours.
The American Diabetes Association recommends that everyone taking insulin, or anyone at high risk for severe low blood sugar, should have a glucagon prescription on hand. Family members, school staff, coworkers, and caregivers should know where it’s kept and how to use it. Newer formulations that come as nasal sprays or prefilled syringes are preferred over the older powder-and-water kits, because they don’t require mixing and can be given faster by someone without medical training.
Side Effects of Glucagon
When glucagon is given as a medication, side effects are common but usually short-lived. In clinical trials of subcutaneous injection, nausea affected about 32% of recipients and vomiting about 36%. A temporary drop in blood pressure occurred in roughly 23% of people, and about the same percentage reported feeling weak. Headache, dizziness, and drowsiness each showed up in 7 to 13% of participants. Injection site swelling and redness were the most frequent reactions overall, affecting more than half of those who received subcutaneous doses.
Intramuscular injection tends to cause fewer side effects. In that group, nausea occurred in about 17% and vomiting in 7%. These differences likely reflect how quickly the hormone enters the bloodstream depending on the injection route.
Storing Glucagon at Home
Traditional glucagon emergency kits contain a powder that must be mixed with sterile water before injection. These kits should be stored at room temperature (around 20 to 25°C) and have a shelf life of about 24 months from manufacture. Once mixed, the solution must be used immediately, and any leftover portion has to be discarded because glucagon degrades within 24 hours after reconstitution. Newer ready-to-use products, including nasal sprays and prefilled auto-injectors, eliminate this mixing step entirely, which is a significant advantage in a panicked emergency situation.