Low blood sugar, or hypoglycemia, is a reading below 3.9 mmol/L (70 mg/dL), and below 3.0 mmol/L (54 mg/dL) is more serious. Here is how lows are classified, what your body does as glucose falls, and what the evidence says about treating and preventing them.
Your hands start to shake in the grocery line, or you wake at 3 a.m. sweating with your heart pounding. Hypoglycemia, or low blood sugar, is a common side effect of insulin and of pills that make the pancreas release more insulin. Diabetes Canada’s 2023 guideline notes that up to 65% of people using these medications report at least one low a year, with lows more frequent in type 1 diabetes 1.
This article explains how lows are classified, what your body does as glucose falls, the most common triggers, how guidelines describe treatment, why warning signs can fade and what research shows about getting them back. It is educational. Your own plan for preventing and treating lows should come from your diabetes care team.
In 2017, the International Hypoglycaemia Study Group set out three levels of hypoglycemia in a joint position statement of the American Diabetes Association and the European Association for the Study of Diabetes 2. Diabetes Canada adopted the same three levels in its 2023 update and linked each one to typical symptoms 1.
| Level | Glucose | What it means |
|---|---|---|
| 1 | Below 3.9 mmol/L (70 mg/dL) | Alert level; warning signs such as shaking or sweating |
| 2 | Below 3.0 mmol/L (54 mg/dL) | Clinically important; brain symptoms such as poor concentration |
| 3 | Any reading | Severe; you need someone else’s help to treat it |
Level 1 is an alert value that tells you to act. The study group chose 3.0 mmol/L (54 mg/dL) as the line for level 2 because lows below it are tied to weakened hormone defences and to loss of warning signs, two problems this article covers below 2. Level 3 is defined by what happens to the person, so it applies whatever the meter or sensor shows.
In people without diabetes, a falling glucose sets off a series of defences. The pancreas releases less insulin, and that drop in insulin inside the pancreas helps signal the release of glucagon, which tells the liver to put glucose back into the blood 3. Adrenaline is released too. In a Washington University study, researchers lowered glucose step by step in 10 healthy volunteers. Glucagon and adrenaline release began at about 3.8 mmol/L (68 to 69 mg/dL) and growth hormone at about 3.7 mmol/L (66 mg/dL). Symptoms appeared only at about 2.9 mmol/L (53 mg/dL) 4. The body normally starts correcting a low before you can feel it.
Symptoms come in two groups 1:
| Autonomic (warning) signs | Neuroglycopenic (brain) signs |
|---|---|
| Trembling | Difficulty concentrating |
| Pounding heart | Confusion |
| Sweating | Weakness or drowsiness |
| Anxiety | Changes in vision |
| Hunger or nausea | Slurred speech |
| Tingling | Headache or dizziness |
Autonomic signs come from adrenaline and the nervous system and act as the early warning. Neuroglycopenic signs mean the brain itself is short of fuel, which is why a low can make it hard to think clearly enough to treat it.
Diabetes changes this picture. Injected or pumped insulin keeps working whether glucose is high or low, so the first defence is missing for anyone who uses insulin. In type 1 diabetes and in advanced type 2 diabetes, the glucagon response is often lost as well, probably because the pancreas no longer makes enough of its own insulin to send the signal 3. That leaves adrenaline as the main remaining defence, and adrenaline can weaken too 3.
Hypoglycemia levels from the International Hypoglycaemia Study Group, with the glucose levels at which defences and symptoms began in a study of healthy volunteers.
Most lows come from a mismatch between insulin action and what the body needs at that moment, made worse by defences that are weaker than normal 3. The main medications involved are insulin and insulin secretagogues, pills such as sulfonylureas and meglitinides that make the pancreas release insulin 1. A smaller or later meal than planned, a dose matched to more food than you ate, or more activity than usual can all tip the balance.
Diabetes Canada lists the main risk factors for severe lows. They include a previous severe low, older age, a low or high A1c, impaired awareness of lows, long duration of diabetes or insulin treatment, nerve damage, reduced kidney function, food insecurity and reduced health literacy 1.
Muscles use more glucose during activity and for some time afterward. Diabetes Canada notes that exercise late in the day or in the evening can raise the risk of an overnight low in type 1 diabetes. Its guideline describes several ways to lower the risk around exercise, such as adjusting carbohydrate or insulin, which should be planned with your care team 5. Diabetes Canada’s hypoglycemia chapter adds that the body’s adrenaline response to a low is weaker after exercise 1.
Alcohol can cause a low hours after the last drink. In a controlled study in Bournemouth, England, six men with type 1 diabetes drank either dry white wine (0.75 g of alcohol per kg of body weight, about 50 g for a 70 kg man) or water at 9 p.m. Overnight glucose was similar on both occasions. The next morning, fasting and post-breakfast glucose were much lower after wine, and from about 10 a.m. five of the six men needed treatment for hypoglycemia, with lows between 1.9 and 2.9 mmol/L (34 to 52 mg/dL). None did after water 6. The study was tiny, but it shows why the morning after drinking deserves attention. Alcohol also blunts the adrenaline response to a low 1. Our article on alcohol and blood sugar covers carbohydrate in drinks and what guidelines say about limits.
Overnight lows are easy to miss. Diabetes Canada notes that lows without symptoms overnight are common and often last more than four hours, and that severe lows with seizures are more likely at night than during the day 1. Sleep itself dampens the alarm. In a study of eight teenagers with type 1 diabetes, adrenaline during a low of 2.8 mmol/L (50 mg/dL) peaked at 70 pg/mL while they slept, compared with 238 to 296 pg/mL when the same teenagers were awake 7. For people at risk, Diabetes Canada recommends CGM or more frequent checks, including during sleeping hours, to find lows that would otherwise go unnoticed 1.
Your care team’s plan comes first. As a reference point, here is how Diabetes Canada’s 2023 guideline describes treating a low in adults 1:
The guideline’s examples of 15 g of carbohydrate include 4 glucose tablets, 15 mL (3 teaspoons) or 3 packets of table sugar dissolved in water, 5 sugar cubes, 150 mL of juice or regular soft drink, 6 Life Savers, or 15 mL (1 tablespoon) of honey 1. Tablet sizes vary, so check the label. The guideline also notes that milk and orange juice raise glucose more slowly than glucose or sucrose, and that glucose gel is slow, raising glucose by less than 1.0 mmol/L in 20 minutes 1.
Glucagon prompts the liver to release glucose, and it is the main treatment when someone can’t safely swallow. Traditional kits require mixing a powder with liquid before injecting 8. Diabetes Canada notes that 1 mg injected under the skin or into a muscle raises glucose from about 3.0 to 12.0 mmol/L (54 to 216 mg/dL) within 60 minutes 1.
Nasal glucagon (3 mg) is given into the nose. Diabetes Canada reports that it works as well as injected glucagon in type 1 diabetes and in insulin-treated type 2 diabetes. When caregivers who had been taught both methods were tested, 93% gave a complete dose with the nasal device compared with 13% with an injection kit, and they did it faster (16 seconds vs 113 seconds) 1.
Ready-to-use liquid glucagon skips the mixing step. In a randomized, double-blind trial of 170 adults with type 1 diabetes, a ready-to-use analogue called dasiglucagon raised glucose by at least 1.1 mmol/L (20 mg/dL) in a median of 10 minutes, compared with 12 minutes for standard reconstituted glucagon and 40 minutes for placebo 8. Which products are available varies by country and changes over time, so ask your pharmacist what you can get. Diabetes Canada recommends that the support people of anyone at risk of a level 3 low learn how to give glucagon 1.
Impaired awareness of hypoglycemia means the early autonomic warning signs no longer come first. They appear at about the same glucose level as the brain symptoms, or lower 1. By the time you notice something is wrong, thinking may already be affected.
In an Edinburgh study of 518 randomly selected adults with type 1 diabetes, 19.5% had impaired awareness. They were older, had lived with diabetes longer and reported about six times as many severe lows in the previous year (2.36 vs 0.38 episodes per person) 9. An earlier prospective study from the same centre followed 60 people with type 1 diabetes for a year. Among those with impaired awareness, 66% had at least one severe low (2.8 episodes per person per year), compared with 26% (0.5 per year) of those with normal awareness 10. At the University of Virginia, 78 adults with type 1 diabetes kept diaries for six months. People who said their awareness was reduced were usually right. The 39 people with reduced awareness had 50 severe lows, against 17 among the 39 who felt their lows normally 11.
Philip Cryer at Washington University described the mechanism as hypoglycemia-associated autonomic failure. Recent lows shift the body’s thresholds, so the next low triggers less adrenaline and fewer warning symptoms. That makes further lows more likely, creating a cycle. Exercise and sleep can cause similar effects 3. Diabetes Canada adds long duration of diabetes, genetic factors and nerve damage to the list of risk factors 1.
Diabetes Canada recommends screening anyone at risk at each clinic visit, using a careful history or a validated tool such as the Gold or Clarke score 1. Research trials have used a Gold score of 4 or more to define impaired awareness 12.
The most consistent finding is that awareness can return when lows are strictly avoided. In Perugia, Italy, eight people with relatively short-duration type 1 diabetes and impaired awareness followed a program to meticulously prevent lows. Lows fell from about one every two days to about one every three weeks. A1c rose from 5.8% to 6.9% (40 to 52 mmol/mol), and by three months most hormone responses and warning symptoms had returned close to normal 13. Cryer’s review concluded that in most affected people, the problem is largely reversible with as little as 2 to 3 weeks of scrupulous avoidance of lows 3.
The UK HypoCOMPaSS trial tested this in 96 adults who had lived with type 1 diabetes for an average of 29 years. Everyone received education and support aimed at rigorously avoiding lows without letting overall control slip. Participants were also randomly assigned to a pump or injections and to real-time CGM or fingerstick checks. Over 24 weeks, time spent at or below 3.0 mmol/L (54 mg/dL) fell from 53 to 24 minutes a day, the average Gold score improved from 5.1 to 4.1, and severe lows dropped from 8.9 to 0.8 episodes per person per year, with no worsening in A1c. Awareness improved by a similar amount whether people used a pump or injections, CGM or fingersticks 14.
For people with impaired awareness, Diabetes Canada recommends avoiding hypoglycemia with individualized glucose targets. Where appropriate, that can include the care team reducing or stopping medications that cause lows for up to three months 1. Any change to insulin or other medication should be made with your diabetes team.
Continuous glucose monitoring shows lows you would otherwise miss. In the Dutch IN CONTROL crossover trial, 52 adults with type 1 diabetes and impaired awareness used real-time CGM for 16 weeks and fingerstick checks for 16 weeks. With CGM, time spent at or below 3.9 mmol/L (70 mg/dL) fell from 11.4% of the day to 6.8% (from about 2.7 hours to 1.6 hours). Time between 4.0 and 10.0 mmol/L (72 to 180 mg/dL) rose from 55.4% to 65.0%, and severe lows dropped from 34 to 14 12. The trial was funded by Eli Lilly and Sanofi.
In the German HypoDE trial, 149 adults with type 1 diabetes on multiple daily injections, who had impaired awareness or a severe low in the previous year, were randomized to real-time CGM or continued fingerstick checks for 26 weeks. Episodes at or below 3.0 mmol/L (54 mg/dL) lasting at least 20 minutes fell from 10.8 to 3.5 per 28 days with CGM. In the control group they barely changed (14.4 to 13.7), and overall CGM cut these episodes by 72% 15. Dexcom, which made the CGM used, funded the trial.
CGM is a tool, and the avoidance strategy still matters. In HypoCOMPaSS, awareness improved by a similar amount with or without CGM when everyone received strong education and support 14.
Diabetes Canada recommends that at every visit, your care team review your recent lows. That includes what contributed, how often they happen, which symptoms you had, whether you recognized them, how severe they were, how you treated them, and the risk of driving with hypoglycemia 1. A record that captures those details makes the conversation faster and more accurate.
Driving needs particular care because the brain symptoms of a low, such as confusion and changes in vision, are dangerous behind the wheel. Ask your team what checks they want before and during driving, and whether any licensing requirements apply to you.
If you want someone close to you to know about a low, Glyve’s Beacon lets you prepare a message to a trusted contact with your latest reading, your logged active insulin and, if you choose, your location. You review the message and send it yourself. Beacon doesn’t monitor you, doesn’t send anything automatically and isn’t an emergency service. In an emergency, call 911.
Lows are classified into three levels 1, 2. Level 1 is below 3.9 mmol/L (70 mg/dL), an alert level; level 2 is below 3.0 mmol/L (54 mg/dL), a clinically important low; and level 3 is a severe low at any reading, when you need someone else's help to treat it.
Symptoms come in two groups: autonomic (warning) signs such as trembling, pounding heart and sweating, and neuroglycopenic (brain) signs such as difficulty concentrating, confusion, changes in vision and slurred speech 1. Warning signs come from adrenaline and the nervous system; brain signs mean the brain itself is short of fuel.
For level 1 or 2 lows in adults, Diabetes Canada's 2023 guideline describes 15 g of fast-acting carbohydrate, preferably glucose or sucrose tablets or a solution, a recheck after 15 minutes, and another 15 g if glucose is still below 3.9 mmol/L (70 mg/dL) 1. Your care team's plan comes first.
With impaired awareness of hypoglycemia, warning signs appear at about the same glucose level as brain symptoms, or lower 1. Recent lows shift the body's thresholds, so the next low triggers less adrenaline and fewer warning symptoms, making further lows more likely 3. Awareness can return when lows are strictly avoided.
Hypoglycemia is a common side effect of insulin and of pills that make the pancreas release more insulin. Diabetes Canada's 2023 guideline notes that up to 65% of people using these medications report at least one low a year, with lows more frequent in type 1 diabetes 1.
When you log a low in Glyve, add the context your care team will ask about: what you ate and when, insulin, exercise, alcohol, how you felt, how you treated it and how long recovery took. Glucose can come in from Apple Health or your CGM company’s sharing service, though readings may arrive later than in the CGM’s own app. The day and week views place each logged moment on your glucose line with your target range shaded, so you can see whether lows cluster after evening exercise, overnight or on certain days. Insulin on board, based on the durations you set, shows how much logged insulin was still active. A PDF report or CSV export carries this to your next appointment. Glyve has no low-glucose alarms, and it shows what happened together without telling you what caused a low.
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