Low blood sugar (hypoglycaemia)
Hypoglycaemia means blood glucose has dropped below 4 mmol/L. Nearly always it happens to people treating diabetes with insulin or with tablets that push the…
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Medicines commonly prescribed for Low blood sugar (hypoglycaemia)
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: INJECTABLE, 100 U/mlActive substance: insulin aspartManufacturer: Novo Nordisk A/SPrescription requiredDosage form: INJECTABLE, 100 U/mlActive substance: insulin aspartManufacturer: Novo Nordisk A/SPrescription requiredDosage form: INJECTABLE, 100 IU/mLActive substance: insulin (human)Manufacturer: Lilly S.A.Prescription required
Hypoglycaemia means blood glucose has dropped below 4 mmol/L. Nearly always it happens to people treating diabetes with insulin or with tablets that push the pancreas to release more of its own. The episode is short, and most people sort it out themselves in ten or fifteen minutes — but only if they know what to do and have something sugary within reach. The danger is not the number itself: the brain runs on glucose and keeps no reserve, so when glucose runs low the ability to think and act disappears before there is time to react.
How a low feels
The first warnings do not come from the brain but from the surge of adrenaline the body uses to push glucose back up:
- sudden hunger, sometimes with nausea;
- trembling hands, weak legs, cold clammy sweat;
- pounding heart, anxiety, irritability for no reason;
- pallor, tingling or numbness around the lips.
If nobody steps in and glucose keeps falling, it is the brain itself that runs short, and the picture changes: a fogged head, trouble finding words, blurred or double vision, odd behaviour that looks like drunkenness from the outside, drowsiness. After that come seizures and loss of consciousness.
A night-time low happens below the level of awareness, which is what makes it treacherous. It gives itself away through a pillow soaked in sweat, vivid dreams and shouting in sleep, headache and exhaustion on waking, and an unexplained high fasting reading.
Loss of warning signs deserves its own note. In someone with long-standing diabetes and frequent lows, the adrenaline response gradually fades and confusion becomes the first symptom. This is the most dangerous version, because that person can no longer help themselves. If you have stopped feeling a low coming, tell your doctor: the warning usually returns after a few weeks of strictly avoiding low readings.
What to do in the first few minutes
The routine is simple and always the same: about 15 grams of fast carbohydrate, wait, then check. Fifteen grams is a small glass of fruit juice or ordinary sugary fizzy drink (never diet or zero), three or four glucose tablets, a tube of glucose gel, or a tablespoon of sugar or honey.
- Sit down first. Standing risks a fall, and this is not a moment to be driving.
- Take the fast sugar and wait 15 minutes without adding more.
- Check your glucose. If it is still below 4 mmol/L, repeat the dose and wait another 15 minutes.
- Once it has come up, eat something slower — a sandwich, cereal, biscuits — or bring your next meal forward if it is due soon. Otherwise the whole thing repeats within the hour.
Chocolate, ice cream and pastries are wrong for the first step: fat slows absorption and the sugar arrives too late. So is eating extra "to be safe" — after overshooting, glucose climbs, a correction dose goes in, and the see-saw starts again. If you have no meter to hand and the symptoms fit, treat it as a low: an error in that direction is harmless, an error the other way is not.
Severe hypoglycaemia: when to call an ambulance
A low is called severe when the person can no longer deal with it alone: they cannot swallow, cannot answer, or are unconscious. Then:
- Put nothing in their mouth — no drink, no food, no sugar under the tongue. All of it will go into the airway.
- Lay them on their side with the head tilted slightly back so the airway stays clear.
- Give glucagon if you have it and know how to use it: an injection into the thigh or a nasal powder. It brings glucose up within 10 to 15 minutes.
- When they come round and can swallow safely, give a sugary drink and then some slower carbohydrate.
- Stay with them until they have fully recovered.
Call an ambulance (in European countries, the single number 112) if the person is unconscious or fitting and there is no glucagon or you do not know how to give it; if there is no improvement ten minutes after glucagon; if the low followed drinking alcohol, because glucagon barely works then; or if episodes come one after another.
One more situation cannot be handled at home. If the glucose was driven down by sulfonylurea tablets — gliclazide, glimepiride, glibenclamide — the low can last many hours and come back after everything appears settled. That person needs to be seen the same day, and older people are usually kept under observation in hospital. The same applies to any hypoglycaemia in someone who does not have diabetes: it is not an episode but a symptom, and it needs looking into straight away.
Why glucose falls in diabetes
Diabetes medicines lower blood glucose — sometimes more than that particular day required. The usual triggers:
- the dose of insulin or tablets is too large for the food and activity of the day;
- a meal was skipped or delayed, or carried less carbohydrate than expected;
- unaccustomed physical work or exercise: glucose falls not at the time but hours later, sometimes during the following night;
- alcohol — the liver is busy clearing it and stops releasing glucose, so the low arrives late, in the small hours, long after the drinking;
- insulin injected into an area of lipohypertrophy: the lump left by repeated injections into one spot absorbs unpredictably;
- vomiting and diarrhoea, which stop carbohydrate being absorbed;
- insulin needs have dropped — weight loss, declining kidney function, a newly added thyroid or adrenal problem.
The risk is higher in older people, in long-standing diabetes, in kidney and liver disease, and in anyone trying to keep glucose as close to ideal as possible. Sometimes no explanation turns up, and that too is a reason to review the regimen rather than shrug it off.
When there is no diabetes
In someone without diabetes the metabolism will not let glucose fall: the liver releases its stores and the pancreas switches insulin off. A confirmed low outside diabetes is therefore rare and always needs an explanation. What gets looked for:
- Insulinoma — a small pancreatic tumour producing insulin on its own. Episodes come on fasting and at night, and for years get put down to nerves, epilepsy or a psychiatric diagnosis. It is almost always benign, and surgery cures it.
- Reactive hypoglycaemia — weakness and shaking one to three hours after a meal heavy in fast sugars. It is commoner after stomach surgery. The treatment is not a drug but smaller, more frequent meals with protein and fibre.
- Adrenal insufficiency and growth hormone deficiency: alongside the low readings come fatigue, weight loss, salt craving and low blood pressure.
- Severe liver disease, kidney failure, sepsis, prolonged starvation — here a low says the underlying illness is far advanced.
- Medicines and alcohol. Accidental or deliberate use of someone else's insulin or diabetes tablets belongs here, and is worth considering when a low appears in a person living alongside someone with diabetes.
The decisive test is taken during the low itself: glucose, insulin, C-peptide and ketones all drawn at the same moment. That single set separates most of the causes, which is why bloods taken on a quiet day usually show nothing.
How to have fewer lows
- Always carry fast sugar. Glucose tablets or a small carton of juice in a pocket, in the car, in the sports bag, by the bed.
- Tell family and colleagues what a low looks like and what to do. Arguing with a confused person is pointless — the people around have to act on their own initiative.
- Keep glucagon at home if you use insulin, and show your household where it is and how it works.
- Do not skip meals or leave a long gap after insulin has gone in.
- Plan around exercise: check before, during and after, add carbohydrate or reduce the dose in advance, and after an evening session check again before bed.
- Alcohol only with food and without cutting the evening meal; check before sleep and again in the morning.
- Rotate injection sites so that lumps do not form.
- Driving: check before setting off and every couple of hours on a long journey, and keep glucose in the car. If you feel a low, pull over, switch off the engine and move out of the driver's seat. Do not drive on until 45 minutes after the reading has recovered: the head clears later than the meter does.
- Ask about the technology. Continuous glucose monitoring warns of a fall before it happens and is particularly valuable for anyone who has lost their warning symptoms or has lows overnight.
What to raise with your doctor
A single low that you dealt with easily does not change the treatment. It is worth booking an appointment if lows happen more than once a week, if you have had even one severe episode, if they come at night, if you have stopped noticing them coming, or if you have started skipping meals out of fear of high readings. A short log helps: time, reading, and what came before it — food, dose, exercise, alcohol.
Your doctor will review doses and timings, check kidney and thyroid function, look at injection technique and sites, and if necessary swap a sulfonylurea for medicines that do not cause hypoglycaemia in their own right. Often the answer is not a new drug but removing something unnecessary and moving one dose to another time of day. Discuss your personal glucose targets as well: for an older person, or for anyone who has already had a severe low, they should be looser, and that is sound strategy rather than a concession.
Online consultation
Hypoglycaemia can be worked through almost entirely at a distance, because what matters here is figures and circumstances rather than examination. The doctor will go through the download from your meter or sensor, find the pattern that is hard to spot in your own log, and explain which dose or which meal sits behind the night-time falls. Online you can adjust insulin doses, review injection technique, build a plan for training and travel, talk through alcohol and driving, and teach the household to use glucagon. If a low has turned up in someone without diabetes, the doctor will say which blood tests to have and at exactly which moment, so that time is not wasted. And separately, they will name the signs that mean calling an ambulance rather than writing to the clinic.
This material is for information only and does not replace medical advice.
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