Mounjaro and low blood sugar (hypoglycaemia)

In short

Low blood sugar is very common (more than 1 in 10) when Mounjaro is used with a sulfonylurea or insulin
With metformin alone low blood sugar is uncommon (up to 1 in 100)
SURPASS trials: 10% to 14% on a sulfonylurea and 14% to 19% on basal insulin had low blood sugar
SURMOUNT-2: 4.2% on tirzepatide against 1.3% on placebo, with no severe episodes
Treat below 4mmol/L with 15 to 20g of fast sugar and recheck in 10 to 15 minutes
DVLA: do not drive with a glucose of 4.0mmol/L or below

Mounjaro rarely causes low blood sugar on its own. Tirzepatide boosts insulin release only when glucose is raised, so the risk is low without diabetes or with metformin alone. The risk becomes very common, more than 1 in 10, when Mounjaro is combined with insulin or a sulfonylurea such as gliclazide. Treat a reading below 4mmol/L with 15 to 20g of fast-acting sugar and recheck after 10 to 15 minutes.

How often low blood sugar happens

The SmPC gives frequencies from the type 2 diabetes trials, split by the medicines taken alongside Mounjaro.

Taken with Mounjaro	Frequency of low blood sugar
A sulfonylurea or insulin	Very common (more than 1 in 10)
Metformin and an SGLT2 inhibitor	Common (up to 1 in 10)
Metformin alone	Uncommon (up to 1 in 100)

In the SURPASS 1 to 5 trials, low blood sugar below 3.0mmol/L or a severe episode occurred in 10% to 14% of people when tirzepatide was added to a sulfonylurea. With basal insulin the figure was 14% to 19%.

The SURMOUNT-2 weight loss trial enrolled adults with type 2 diabetes. Low blood sugar affected 4.2% on tirzepatide against 1.3% on placebo. The risk was higher in people taking a sulfonylurea, and no severe episodes were reported.

Why Mounjaro on its own carries a low risk

Tirzepatide acts on GIP and GLP-1 receptors. Both prompt the pancreas to release insulin, but only when blood glucose is raised. When your level falls back to normal, the push on insulin fades. This glucose-dependent action is why people without diabetes rarely get true hypoglycaemia on Mounjaro.

Insulin and sulfonylureas work differently. Insulin lowers glucose whatever the level, and sulfonylureas make the pancreas release insulin regardless of your glucose. Add Mounjaro, which cuts appetite and food intake, and glucose can drop too far.

Symptoms of low blood sugar

The UK leaflet lists these signs:

Headache
Drowsiness
Weakness
Dizziness
Feeling hungry
Confusion
Irritability
A fast heartbeat
Sweating

Guy's and St Thomas' NHS Foundation Trust adds shaking, tingling lips, anxiety, paleness and trouble concentrating. A hypo is a glucose level below 4mmol/L. Symptoms vary from person to person, and some people with long-standing diabetes notice fewer warning signs.

How to treat a hypo: the 15g rule

Check your glucose if you can. Treat anything below 4mmol/L.
Take 15 to 20g of fast-acting carbohydrate. Examples are 4 to 6 glucose tablets, 3 to 4 jelly babies, a tube of glucose gel, or a 150 to 200ml glass of fruit juice or non-diet fizzy drink.
Recheck after 10 to 15 minutes. If your level is still below 4mmol/L, repeat step 2.
Once your level is back up, eat a starchy snack if your next meal is not due. A slice of toast, two digestive biscuits or a glass of milk works.

Chocolate and biscuits act too slowly for the first step because the fat delays absorption.

A severe hypo

If someone is drowsy, confused and unable to swallow, or unconscious, do not give food or drink. Use a glucagon injection if one has been prescribed and a trained person is present, or call 999.

Adjusting your diabetes medicines

The SmPC says a lower dose of a sulfonylurea or insulin may be considered to cut the risk of low blood sugar when you start tirzepatide. The leaflet tells you your doctor may need to change these doses.

Your prescriber may lower your gliclazide or insulin at the start, then again as your Mounjaro dose steps up or your weight falls. Check your glucose more often in the first weeks and after each dose increase. Do not stop or change insulin or tablets without advice.

Days of vomiting or eating very little raise the risk further. The sick day rules page explains what to do with diabetes medicines when you are unwell.

Driving and low blood sugar

The SmPC says tirzepatide itself has no or negligible effect on driving. With a sulfonylurea or insulin, low blood sugar may reduce your concentration, and the leaflet advises you not to drive or use machines if you get any signs of a hypo.

The DVLA guide for drivers on insulin sets these rules:

Check your glucose just before you start driving and at least every 2 hours on a journey.
Do not drive if your glucose is 4.0mmol/L or below.
Between 4.0 and 5.0mmol/L, eat a fast-acting carbohydrate before driving.
If a hypo starts while driving, stop safely, switch off the engine and remove the keys.
Wait at least 45 minutes after your glucose returns to 5.0mmol/L or above before driving again.

Car and motorcycle drivers must tell the DVLA about 2 or more episodes of severe hypoglycaemia while awake in 12 months, or a severe episode while driving. If you take a sulfonylurea or a non-insulin injection, GOV.UK says to check with your doctor or nurse whether your treatment means you need to tell the DVLA. Bus and lorry drivers have stricter rules.

Low blood sugar and your eyes

Fast improvements in glucose control can cause a temporary worsening of diabetic retinopathy. If you have diabetic eye disease, see the diabetic eye changes page.

If you do not have diabetes

Shakiness, weakness or lightheadedness on Mounjaro without diabetes is usually from eating too little, a long gap between meals or not drinking enough. Eat something small every 3 to 4 hours and keep fluids up. The eating too little and dizziness pages cover these causes. If symptoms keep returning, ask your GP to test your blood sugar.

When to get help

Call 999 or go to A&E if:

Someone is unconscious, having a seizure or too drowsy to swallow
A hypo does not improve after two or three treatments with fast sugar
Confusion or strange behaviour continues after glucose returns to normal

Call 111 or see a GP today if:

You have had a severe hypo needing help from another person
You get repeated readings below 4mmol/L on the same day or over a few days
You are vomiting and cannot keep food or sugary drinks down while on insulin or a sulfonylurea
You have lost the warning signs of a hypo

Mention at your next check if:

You have had one or two mild hypos since starting Mounjaro
Your glucose readings are falling and you want your gliclazide or insulin reviewed
You need advice on DVLA rules for your treatment

Report hypos linked to Mounjaro to your prescriber and, if you wish, through the MHRA Yellow Card scheme.

Questions people ask

Does Mounjaro cause low blood sugar?

Rarely on its own. Tirzepatide increases insulin release only when glucose is raised, so people without diabetes and people on metformin alone have a low risk. The risk is high when Mounjaro is combined with insulin or a sulfonylurea such as gliclazide.

Can you get low blood sugar on Mounjaro without diabetes?

True hypoglycaemia is unlikely in people without diabetes. Feeling shaky, weak or lightheaded after a long gap without food is more often from eating too little or dehydration. If symptoms keep returning, ask your GP to check your blood sugar.

What should I eat if my blood sugar drops on Mounjaro?

Take 15 to 20g of fast-acting sugar, such as 4 to 6 glucose tablets, 3 to 4 jelly babies or a 150 to 200ml glass of fruit juice or non-diet fizzy drink. Recheck after 10 to 15 minutes and repeat if still below 4mmol/L. Then eat a starchy snack or your next meal.

Will my diabetes medicines be reduced when I start Mounjaro?

Possibly. The SmPC says a lower dose of a sulfonylurea or insulin may be considered to reduce the risk of low blood sugar. Your prescriber decides, often at the start and again as your dose steps up. Do not change insulin or tablets without advice.

Can I drive on Mounjaro if I take insulin?

Yes, if you follow DVLA rules. Check your glucose just before driving and at least every 2 hours on a journey, and do not drive at 4.0mmol/L or below. If you have a hypo while driving, stop safely, remove the keys and wait at least 45 minutes after your level is back to 5.0mmol/L or above.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Mounjaro and low blood sugar (hypoglycaemia). Site: Mounjaro Info (https://mounjaroinfo.co.uk/side-effects/mounjaro-low-blood-sugar/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

Mounjaro rarely causes low blood sugar on its own because its effect on insulin depends on glucose levels. The risk rises sharply with insulin or a sulfonylurea such as gliclazide, where low blood sugar is very common, and your prescriber may lower those doses. Treat a reading below 4mmol/L with 15 to 20g of fast-acting sugar, recheck after 10 to 15 minutes, and never drive with a glucose of 4mmol/L or below.

Low blood sugar is very common (more than 1 in 10) when Mounjaro is used with a sulfonylurea or insulin
With metformin alone low blood sugar is uncommon (up to 1 in 100)
SURPASS trials: 10% to 14% on a sulfonylurea and 14% to 19% on basal insulin had low blood sugar
SURMOUNT-2: 4.2% on tirzepatide against 1.3% on placebo, with no severe episodes
Treat below 4mmol/L with 15 to 20g of fast sugar and recheck in 10 to 15 minutes
DVLA: do not drive with a glucose of 4.0mmol/L or below

Cite as: Mounjaro Info, "Mounjaro and low blood sugar (hypoglycaemia)", https://mounjaroinfo.co.uk/side-effects/mounjaro-low-blood-sugar/, reviewed 22 October 2026.