Hypoglycemia

What it is

Hypoglycemia (low blood sugar) is a condition in which blood glucose drops below 3.9 mmol/L (70 mg/dL), triggering an emergency hormonal response and symptoms that range from shakiness and sweating to, in severe cases, seizures or loss of consciousness. Also called low blood glucose, hypoglycemia is most common in people with diabetes who use insulin or certain glucose-lowering medications — a large global study found that 4 in 5 people with type 1 diabetes and nearly half of those with type 2 diabetes on insulin reported at least one low blood sugar episode over a four-week period.

The brain depends almost entirely on glucose for fuel and stores almost none of its own, which is why even a moderate drop in blood sugar can impair cognition within minutes. In Canada, where roughly 3.7 million people live with diabetes (Diabetes Canada, 2023), hypoglycemia is one of the most common acute complications managed in both primary care and emergency settings. Recurring or severe episodes carry real long-term risks: impaired cognitive function, increased cardiovascular events, and, in extreme cases, permanent neurological injury.

Causes and mechanism

The body maintains blood glucose through a balance of insulin (which lowers glucose) and counter-regulatory hormones — primarily glucagon, cortisol, adrenaline, and growth hormone — that raise it. Hypoglycemia occurs when this balance tips too far toward glucose removal or when counter-regulatory responses fail.

In people with diabetes, the most common triggers are:

• Insulin overdose or miscalculated dosing
• Sulfonylureas (e.g., glyburide, glipizide) or meglitinides, which stimulate insulin release regardless of blood glucose level
• Delayed or skipped meals after taking insulin or an insulin secretagogue
• Unplanned physical activity without adjusting insulin or carbohydrate intake
• Alcohol consumption, which blocks hepatic glucose production (gluconeogenesis) — particularly dangerous when combined with insulin or sulfonylureas

In people without diabetes, causes include:

Cause	Mechanism
Adrenal insufficiency (Addison's disease)	Cortisol and adrenaline deficiency impairs counter-regulatory glucose release
Growth hormone deficiency	Blunted counter-regulatory response, especially in children
Insulinoma	Rare insulin-secreting pancreatic tumour causing endogenous hyperinsulinism
Reactive hypoglycemia	Glucose drop 2–4 hours post-meal, often linked to insulin resistance or post-bariatric surgery
Severe liver disease	Impaired hepatic glucose release
Certain medications	Quinine, high-dose salicylates, some quinolone antibiotics

Symptoms and diagnosis

Symptoms occur in two recognizable phases.

Adrenergic (early) symptoms — driven by the counter-regulatory hormone surge: shakiness, sweating, rapid heartbeat, hunger, anxiety, and pallor. These are the body's warning signals to eat.

Neuroglycopenic (later) symptoms — as the brain is deprived of glucose: difficulty concentrating, confusion, blurred or double vision, slurred speech, weakness, headache, and irritability. Severe hypoglycemia can progress to seizures, loss of consciousness, or coma.

Hypoglycemia unawareness is a clinically important complication in which people with long-standing diabetes lose the ability to feel early adrenergic warning signs. Repeated low blood sugar episodes blunt the counter-regulatory response, meaning glucose can fall to dangerous levels before the person or anyone nearby recognizes a problem.

Diagnosis rests on Whipple's triad: documented low blood glucose at the time of symptoms, plus resolution of those symptoms after glucose is restored. Additional workup for non-diabetic causes may include fasting insulin, C-peptide, and proinsulin levels (to detect endogenous hyperinsulinism), a supervised prolonged fast, or a cortisol/ACTH stimulation test if adrenal insufficiency is suspected. In Canada, these tests are available through LifeLabs and Dynacare, and are typically ordered by an endocrinologist or internist.

Treatment options

Immediate treatment — the 15-15 rule: Consume 15 grams of fast-acting carbohydrate (approximately 4 glucose tablets, 150 mL of fruit juice, or 150 mL of regular — not diet — soft drink), wait 15 minutes, then recheck blood glucose. Repeat if still below 3.9 mmol/L. Fat-containing foods like chocolate slow glucose absorption and are not appropriate for acute treatment.

For severe hypoglycemia (person cannot swallow safely):

• Glucagon injection or nasal glucagon powder (Baqsimi), which can be administered by a trained family member or caregiver — both are available by prescription in Canada
• Intravenous dextrose in a hospital or emergency setting

Prevention and long-term management:

• Regular blood glucose monitoring or continuous glucose monitoring (CGM) with low-glucose alarms — CGM devices such as the FreeStyle Libre and Dexcom G7 are partially covered under several provincial formularies in Canada, including Ontario's Assistive Devices Program for type 1 diabetes
• Insulin dose review and timing adjustments with a diabetes care team
• Education on how exercise, alcohol, and meal timing affect glucose
• Treating underlying endocrine causes: hydrocortisone and fludrocortisone for adrenal insufficiency; growth hormone replacement for GH deficiency; surgical resection for insulinoma

For hypoglycemia unawareness, deliberate avoidance of low blood sugar for several weeks can partially restore counter-regulatory responses and symptom awareness in some patients. CGM with alerts is particularly valuable in this group.

When to see a clinician in Canada

Call 911 or go to the nearest emergency department if someone loses consciousness, has a seizure, cannot safely swallow, or if blood glucose falls below 2.8 mmol/L (50 mg/dL) and does not respond to oral carbohydrate treatment.

Book an appointment with your family physician or nurse practitioner if you are experiencing recurrent hypoglycemia episodes — even mild ones — if you have noticed you no longer feel early warning signs, or if you are having low blood sugar episodes without a diabetes diagnosis. Canadians without a regular primary care provider can access same-day or next-day virtual consultations through platforms such as Maple, Felix, or Cleo, which can arrange urgent referrals to endocrinology where needed.

Limitations and open questions

Research is still emerging on the long-term cardiovascular consequences of recurrent mild hypoglycemia in people with type 2 diabetes — some observational data suggest an association with increased cardiac events, but causality has not been established. The optimal blood glucose threshold for treatment in hospitalized patients remains debated, and institutional protocols vary across Canadian hospitals. Health Canada has not yet issued unified national guidance on CGM coverage criteria, leaving access inconsistent across provinces. The mechanisms underlying hypoglycemia unawareness are not fully understood, and not all patients recover symptom awareness even after sustained glucose avoidance. Evidence on reactive hypoglycemia — including its prevalence and best dietary management — remains limited and somewhat mixed.