Last updated: October 2026
Yes, Mounjaro (tirzepatide) can make you tired. The UK patient leaflet lists feeling tired (fatigue) as a common side effect for people using it for weight loss, affecting up to 1 in 10. Eating much less, fluid loss from sickness or diarrhoea and poor sleep can all add to it. Speak to your prescriber if it doesn’t ease.
Checked against the UK leaflet (revised August 2026) and NHS advice in October 2026.
Is tiredness a side effect of Mounjaro? What the leaflet says
Yes. The UK patient information leaflet for Mounjaro KwikPen lists “feeling tired (fatigue)” as a side effect. It was common (up to 1 in 10 people) in people treated for weight management and type 2 diabetes, and very common (more than 1 in 10) in a heart study of people with type 2 diabetes. The NHS lists it as common too.
Other listed side effects can drain you too:
| Side effect | How common (weight loss use) | Why it matters for energy |
|---|---|---|
| Feeling tired (fatigue) | Common | Listed in its own right |
| Nausea, diarrhoea, vomiting | Very common | Fluid loss and eating less |
| Feeling less hungry | Listed | Fewer calories and nutrients |
| Dizziness, low blood pressure | Common | Can feel weak or light-headed |
| Low blood sugar | Mainly with insulin or a sulphonylurea | Drowsiness, weakness, confusion |
The leaflet says the stomach side effects are most common when you first start and decrease over time in most people. Not everybody gets side effects.
Why Mounjaro can make you so tired
The leaflet doesn’t say why fatigue happens, and there’s no single proven cause. Likely contributors:
- Eating a lot less. Mounjaro reduces appetite and helps you feel full, so you eat less food. A big drop in calories can leave you low on energy. See also tired after eating.
- Dehydration. The leaflet warns that vomiting, nausea or diarrhoea can cause loss of fluids, especially when starting treatment. The NHS lists feeling tired, dizziness and headaches as signs of dehydration.
- Low blood sugar. This is mainly a risk if you also take insulin or a sulphonylurea such as gliclazide. Symptoms include drowsiness, weakness, dizziness and confusion.
- Dizziness and low blood pressure. Both are listed as common in people using Mounjaro for weight loss.
- Poor sleep. Night-time nausea, reflux or a busy mind can break up your nights. See can’t sleep on Mounjaro? for the sleep side.
- Nutrient gaps and muscle loss. A 2025 joint advisory from four US nutrition and obesity societies lists nutritional deficiencies from eating less, and loss of muscle and bone, among the challenges of GLP-1 treatment. Low iron or vitamin B12 can cause tiredness on its own.
Other everyday causes: why am I always tired?
How long does Mounjaro tiredness last?
There’s no official timeline for fatigue. The leaflet says stomach side effects are most common at the start and ease over time for most people, so tiredness linked to them often eases as your body adjusts. Two times to expect a dip:
- The first weeks. The starting dose is 2.5mg once a week for four weeks, then 5mg.
- After each dose increase. Your prescriber may raise the dose in 2.5mg steps, with at least four weeks on each dose, and side effects can return for a while.
Is it worse the day after the injection?
Some people feel flatter in the day or two after their weekly dose, often alongside nausea, though the leaflet doesn’t describe this pattern. Keep a simple diary of injection day, meals, fluids and energy and share it with your prescriber. The leaflet allows you to change your injection day if it has been at least 3 days since your last dose, so ask whether moving it would suit your week.
If you’ve felt tired for a few weeks and it isn’t improving, or it affects daily life, the NHS advises seeing a GP.
What helps tiredness on Mounjaro
- Eat regular small meals, even when you’re not hungry, and follow any diet advice from your prescriber or dietitian. Build meals around protein, plus vegetables and whole grains. See how much protein do I need?
- Drink plenty of fluids, sipping little and often if you feel sick. See how much water should I drink? If you’re losing fluid through sickness or diarrhoea, the NHS says a pharmacist can recommend oral rehydration solutions. See electrolytes.
- Avoid alcohol. The NHS says it’s best to avoid alcohol on tirzepatide because it can increase nausea and vomiting.
- Keep moving gently. The advisory recommends strength training to help protect muscle while you lose weight.
- Protect your sleep: regular bed and wake times and no late caffeine. See afternoon slump.
- Don’t stop or change your dose on your own. The leaflet says not to stop Mounjaro without talking to your doctor.
Our Magnesium Glycinate Sleep Complex is a berry-flavoured drink powder with 148mg of magnesium per serving, from magnesium bisglycinate and citrate, plus glycine, L-theanine and chamomile, passionflower, hops and oat straw extracts. Magnesium contributes to a reduction of tiredness and fatigue. It isn’t a treatment for medicine side effects, so check with your prescriber or pharmacist first and ask how far apart to take it from any other medicines.
Our Reishi Mushroom Adaptogenic Complex is a reishi hot chocolate with cacao and maca; it contains a little natural caffeine, so have it before mid-afternoon. Both are vegan, UK-made and for adults (18+).
Blood tests and supplements: what’s worth checking
No supplement treats Mounjaro side effects. If tiredness lasts, ask your GP whether a blood test for iron, vitamin B12 or vitamin D makes sense. Signs to mention:
- Pale skin, breathlessness or heart palpitations: see iron deficiency symptoms.
- Pins and needles, a sore tongue or memory problems: see vitamin B12 deficiency symptoms.
- Bone pain or aching, weak muscles: see vitamin D deficiency symptoms.
The authorised GB health claims are specific: iron and vitamin B12 each contribute to the reduction of tiredness and fatigue, and magnesium contributes to a reduction of tiredness and fatigue. They help when you’re short of them; they don’t override a medicine side effect. See supplements for energy and magnesium for energy.
The NHS says some supplements and herbal remedies may not mix well with tirzepatide, so tell your doctor or pharmacist about anything you take. See magnesium for Mounjaro. Thinking about CBD? The FSA advises people taking any medication not to take CBD unless under medical direction, so speak to your prescriber first.
Does Mounjaro cause hair loss?
It can. The leaflet lists hair loss as common (up to 1 in 10) in people using Mounjaro for weight management, and the NHS includes it in the common side effects.
The NHS lists weight loss and iron deficiency among the causes of temporary hair loss. The British Association of Dermatologists says marked weight loss can trigger telogen effluvium, a shedding that often starts around 3 months after the trigger, lasts 3 to 6 months and usually gets better without treatment. Eating enough protein and iron-rich foods may help. See why is my hair falling out? and stress and hair loss, and see a GP if you’re worried.
When to get advice or urgent help
| If you have | What to do |
|---|---|
| Tiredness or other side effects that bother you or don’t go away | Speak to your prescriber, GP or pharmacist |
| Signs of dehydration: dark pee, peeing less, dizziness that doesn’t go away | Urgent GP appointment or NHS 111 |
| Low blood sugar signs (shaking, sweating, confusion) on insulin or a sulphonylurea | Treat as your diabetes team advised; get help if it doesn’t improve |
| Severe stomach pain that won’t go away, possibly spreading to your back | Stop Mounjaro and call 999 or go to A&E |
| Swelling of the lips, tongue or throat, or trouble breathing | Call 999 |
Severe, persistent stomach pain can be a sign of acute pancreatitis, which the leaflet calls serious and potentially life-threatening. You can report side effects via the MHRA Yellow Card scheme.
Pregnancy: the leaflet says Mounjaro shouldn’t be used during pregnancy and recommends contraception. If you use the pill, it advises adding a barrier method for 4 weeks after starting and after each dose increase. We don’t recommend our products during pregnancy or breastfeeding.
FAQs
Does Mounjaro make you tired?
It can. The UK leaflet lists fatigue as common in people using Mounjaro for weight loss, affecting up to 1 in 10. Eating less, fluid loss from sickness or diarrhoea and poor sleep can add to it.
How long does Mounjaro tiredness last?
There’s no official timeline. Stomach side effects ease over time for most people, so related tiredness often eases too, though it can return after a dose increase. See a GP if it lasts more than a few weeks.
Is Mounjaro tiredness worse after the injection day?
Some people feel flatter for a day or two after their dose, often with nausea. Keep a diary and tell your prescriber, who can advise on changing your injection day.
Can Mounjaro cause hair loss?
Yes. The leaflet lists hair loss as common in people using it for weight management. Shedding after marked weight loss can start around 3 months later and usually settles without treatment. See a GP if you’re worried.
What helps tiredness on Mounjaro?
Regular small meals with protein, plenty of fluids, no alcohol, gentle activity and good sleep. Don’t change your dose without your prescriber.
Should I take supplements on Mounjaro?
Only after checking with your prescriber or pharmacist, as some supplements and herbal remedies may not mix well with tirzepatide. If tiredness lasts, ask your GP about checking iron, vitamin B12 and vitamin D rather than guessing.
Sources
- emc. Mounjaro KwikPen: patient information leaflet (revised August 2026).
- NHS. Tirzepatide.
- NHS. Dehydration.
- NHS. Acute pancreatitis.
- NHS. Hair loss.
- British Association of Dermatologists. Telogen effluvium.
- Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory. Am J Clin Nutr. 2025;122(1):344-367. PMID 40450457.
- FSA (gov.uk). Cannabidiol (CBD) guidance.
- gov.uk. Great Britain nutrition and health claims register.
This guide is general information, not medical advice. Always follow the advice of your prescriber and the leaflet that comes with your medicine. Evopure makes the Magnesium Glycinate Sleep Complex and Reishi Mushroom Adaptogenic Complex, and isn’t connected with Eli Lilly, which makes Mounjaro.
