Hypoglycaemia from GLP-1 Injections

Hypoglycaemia, or low blood sugar is more common in people taking insulin or certain diabetes medications, but it can happen to those using GLP-1 injections like semaglutide (Wegovy) or tirzepatide (Mounjaro) for weight loss too. Especially if you’re eating much less than usual.

So if you’re feeling shaky, dizzy, or unusually tired after starting your GLP-1 medication, here’s everything you need to know about why that might be happening. Learn what to look out for and how to keep your blood sugar stable while staying on track with your GLP-1 treatment.

What Is Hypoglycaemia?

Hypoglycaemia happens when your blood sugar level drops too low, typically below 4.0 mmol/L. Your body, especially your brain, relies on a steady supply of glucose for energy. When levels dip, even slightly, you can start to feel unwell very quickly.

This is your body’s way of sounding the alarm, and it’s important to act fast.

Common symptoms of low blood sugar:

• Shakiness or trembling
• Sweating or feeling suddenly cold
• Fatigue or weakness
• Dizziness or vertigo (a spinning sensation or feeling off-balance)
• Blurred vision
• Irritability or mood swings
• Hunger, even if you don’t feel like eating
• Racing or pounding heartbeat
• Difficulty concentrating or confusion

In more severe cases, hypoglycaemia can cause fainting, seizures, or loss of consciousness if left untreated.

Recognising these early warning signs is key, especially if you’re taking GLP-1 medications and your eating habits have changed. Acting quickly (by eating or drinking something sugary) can help prevent symptoms from getting worse.

Why Does Hypoglycaemia Happen on GLP-1s?

GLP-1 medications like Wegovy and Mounjaro don’t directly lower blood sugar the way insulin does—but they do change how your body manages food, energy, and digestion. For people using them for weight loss, the most common reason for low blood sugar is simply not eating enough to keep up with your body’s needs.

This can happen when:

• Your appetite drops sharply and you forget to eat
• You’re losing weight quickly, which affects how your body handles glucose
• You’re doing more exercise without adjusting your food intake
• You’ve just started or increased your GLP-1 dose and your body is still adapting

In short, it’s not usually the injection alone—it’s the combination of reduced food intake, shifting habits, and physical changes that can lead to a dip in blood sugar.

When is hypoglycaemia most likely to occur?

• 2–4 hours after taking certain diabetes medications (like insulin or sulfonylureas, if you’re using them together with GLP-1s)
• Between meals, when blood sugar naturally dips
• During or after exercise, especially if you haven’t eaten enough beforehand
• After dose changes, as your body adapts to stronger appetite-suppressing effects
• During rapid weight loss or dietary changes, when your energy intake is lower than usual

Who’s at higher risk?

If you’re using GLP-1s for diabetes:

• Combination therapy – using insulin or sulfonylureas alongside GLP-1s increases your risk
• Timing clashes – when two medications lower your blood sugar at the same time
• Dose adjustments – without matching changes in your food intake

If you’re using GLP-1s for weight loss only:

• Skipping meals or eating very little throughout the day
• Low-carb or restrictive diets that don’t provide steady energy
• Delayed digestion, which slows the release of glucose into your system
• Increased exercise without adjusting what or when you eat

Other contributing factors include:

• Kidney or liver problems, which affect glucose balance
• Recent illness, infection, or stress
• Alcohol consumption
• Certain non-diabetes medications that affect blood sugar

How to Manage Low Blood Sugar on GLP-1s

If you’re at risk of hypoglycaemia, or you’ve already experienced symptoms, there are simple steps you can take to prevent and manage it.

Recognise the Early Signs

• Shakiness or trembling
• Sweating or chills
• Fatigue or weakness
• Hunger, even if you don’t feel like eating
• Dizziness or blurred vision
• Irritability or confusion

Act Quickly

If you think your blood sugar is low:

1. Eat or drink something containing fast-acting sugar, such as:
   • 4-5 glucose tablets
   • 150ml fruit juice
   • 5-6 jelly babies
   • 3 teaspoons of sugar in water
2. Check your blood sugar (if you have a monitor). Recheck after 15 minutes.
3. Follow up with a snack containing protein or complex carbs, like a slice of toast or a small banana with peanut butter.

Prevent Future Episodes

• Don’t skip meals, even if your appetite is low
• Keep quick sugar sources with you at all times
• If you take insulin or sulfonylureas, ask your GP if your dose needs adjusting
• Let your pharmacist or GP know if symptoms happen more than once
• Stay hydrated and avoid excessive alcohol
• Track your symptoms to spot patterns (e.g., time of day, activity, or dose timing)

Important: If you pass out, have a seizure, or feel extremely confused, this could be a severe hypoglycaemic episode. Seek urgent medical attention.

When to Speak to a Healthcare Professional

Even mild symptoms should be discussed with your GP, especially if:

• You’re taking insulin or sulfonylureas
• You’ve had multiple low blood sugar episodes
• You’re unsure if you’re eating enough while on GLP-1s
• You’ve had a recent change in dose, weight, or diet

Your pharmacist or GP can help you adjust your treatment or recommend a nutrition plan to reduce the risk.

FAQs

Can GLP-1 medications cause hypoglycaemia on their own?

Usually not. GLP-1s don’t directly lower blood sugar the way insulin does. But the risk increases when taken with other diabetes medications that do.

What blood sugar level is considered too low?

Anything below 4.0 mmol/L is generally considered hypoglycaemia and should be treated quickly to avoid more serious symptoms.

I don’t have diabetes. Should I worry about low blood sugar?

It’s uncommon, but possible if you’re not eating enough or losing weight very rapidly. Be sure to eat regular meals and stay hydrated.

What should I eat if I feel symptoms coming on?

Start with something sugary (like juice or glucose tablets), then follow up with something longer-lasting like toast or nuts to stabilise your levels.

Should I stop taking my medication if I have hypoglycaemia?

No. speak to your healthcare provider first. There may be other ways to manage symptoms safely, such as adjusting other medications or changing how you eat.