Mounjaro and Hair Loss: Causes, Evidence and Recovery

Yes, hair loss can happen on Mounjaro (tirzepatide). The UK product information lists it as a common side effect, and in the main weight management trials around one in twenty people taking tirzepatide reported hair loss, compared with about one in a hundred on placebo. In most cases it was mild and settled without stopping treatment. The leading explanation is that hair shedding is a response to rapid weight loss and eating less, a pattern called telogen effluvium, rather than the medicine directly damaging hair. This guide explains the evidence, the likely causes, what recovery looks like and when to see a doctor.

What the evidence shows

The UK product information

The Summary of Product Characteristics (SmPC) for Mounjaro, published on the Electronic Medicines Compendium, lists hair loss (alopecia) as a common adverse reaction in people treated for weight management. "Common" is a standard frequency category meaning it may affect up to one in ten people.

The SmPC states that, in the weight management studies, hair loss was reported in 4.9% of patients treated with tirzepatide. It adds that most events were mild and that most people recovered while continuing treatment. Hair loss was reported less often in the type 2 diabetes trials, where average weight loss was smaller. For an overview of the medicine and its licence, see our Mounjaro hub.

SURMOUNT-1

SURMOUNT-1, published in the New England Journal of Medicine in 2022, was the main trial behind Mounjaro's weight management licence. It enrolled adults with obesity, or overweight plus a weight-related condition, who did not have diabetes, and followed them for 72 weeks.

Average weight loss was substantial: around 15% on the 5mg dose and around 20 to 21% on the 10mg and 15mg doses, compared with about 3% on placebo. Alongside this, alopecia was reported as an adverse event in roughly 5% of people across the tirzepatide doses, compared with under 1% on placebo. Hair loss was more often reported by women than men, a pattern also seen in semaglutide trials.

The table below summarises the hair loss findings from the trials behind the two main UK weight-loss injections. Because the trials were separate, with different participants and designs, the figures should not be used to compare the medicines directly.

Sources: SURMOUNT-1 and STEP 1, New England Journal of Medicine; Mounjaro SmPC.

Is it the drug or the weight loss?

This is the key question, and the honest answer is that it is not fully settled. Several points support the idea that weight loss itself is the main driver:

• Hair loss is well documented after other forms of rapid weight loss, including bariatric surgery and very low calorie diets, where no GLP-1 medicine is involved.
• It tends to appear months into treatment, around the time weight loss is fastest, which fits the timing of telogen effluvium.
• It was less common in the diabetes trials, where weight loss was smaller.
• It usually resolved during continued treatment, which would be less expected if the medicine were directly toxic to hair follicles.

That said, the trials were not designed to separate these effects, and researchers have not ruled out other contributing factors. The fairest summary is that hair loss is a recognised side effect of treatment, most likely related largely to the pace and amount of weight loss.

What the trial figures do and do not tell us

Trial data are the most reliable source available, but they have limits when it comes to a side effect like hair loss.

• Hair loss was self-reported. In SURMOUNT-1 and STEP 1, alopecia was recorded as an adverse event when participants or investigators reported it. There was no systematic measurement of hair density, so mild thinning may have been under-reported, and some reports may have reflected normal variation.
• Severity was mostly mild. The SmPC describes most cases as mild. The trials do not tell us how many people felt the hair loss affected their quality of life.
• Follow-up was limited. The trials lasted around 68 to 72 weeks. They give less information about what happens to hair over several years of treatment, or after stopping.
• Participants were selected. People in trials are monitored closely, usually receive lifestyle advice, and may differ from people treated in everyday practice. Hair loss rates outside trials could be higher or lower.
• Women were more affected. Both programmes reported hair loss more often in women. The reasons are not clear, but may include differences in iron stores, hormones and how noticeable thinning is with longer hair.

Post-marketing reports to regulators, such as the MHRA's Yellow Card scheme, add real-world information but cannot show how common a side effect is, because not every case is reported. If you experience hair loss on Mounjaro, you or a healthcare professional can report it through the Yellow Card scheme, which helps the MHRA monitor medicine safety.

Does dose matter?

In SURMOUNT-1, the rate of reported hair loss was broadly similar across the 5mg, 10mg and 15mg doses, at around 5% each. That suggests the dose alone is not a strong predictor, although higher doses produced greater average weight loss. The pace of weight loss, how much people were eating, and individual susceptibility are likely to matter as much as the dose number.

For semaglutide, the UK Wegovy leaflet notes that hair loss is reported more often with the 7.2mg dose than with 2.4mg, which may reflect the greater weight loss seen at the higher dose.

Hair loss after stopping treatment

Some people notice shedding after they stop a GLP-1 medicine. This has not been studied in detail. Possible explanations include a delayed telogen effluvium from weight loss that happened in the preceding months, changes in eating pattern, or other life events. Because of the two-to-four-month delay, hair loss that appears after stopping may reflect what happened during treatment rather than the act of stopping itself. If it persists, a GP can investigate.

Questions to ask your prescriber

If hair loss is worrying you, these questions may help structure the conversation:

1. Is my rate of weight loss within the range you would expect, or faster?
2. Could I stay on my current dose for longer before increasing?
3. Should I have blood tests for iron, thyroid function or vitamins?
4. How much protein should I aim for, given my weight and appetite?
5. Are any of my other medicines known to affect hair?
6. Would you recommend seeing a GP or dermatologist?

Why rapid weight loss can cause hair shedding

The hair growth cycle

Each hair follicle on the scalp cycles independently through three main phases:

1. Anagen (growth): lasts several years. Most scalp hairs, often around 85 to 90%, are in this phase at any one time.
2. Catagen (transition): a short phase of a few weeks.
3. Telogen (resting and shedding): lasts around two to three months, after which the hair falls out and a new one begins to grow.

Losing a moderate number of hairs each day is normal. The NHS notes that it is common to lose between 50 and 100 hairs a day.

Telogen effluvium

Telogen effluvium happens when a stressor causes a larger than usual proportion of follicles to switch from the growth phase into the resting phase at the same time. Because the resting phase lasts a couple of months, the shedding is delayed: people typically notice it two to four months after the trigger.

Common triggers include:

• Rapid or significant weight loss.
• A sharp drop in calorie or protein intake.
• Major illness, surgery or high fever.
• Childbirth.
• Severe emotional stress.
• Some medicines.
• Iron deficiency or thyroid problems.

GLP-1 medicines reduce appetite considerably, especially in the first months. If you are eating much less and losing weight quickly, the body may prioritise essential functions over hair growth, which is not vital for survival.

What telogen effluvium looks like

• Diffuse shedding across the whole scalp rather than bald patches.
• More hairs than usual on the pillow, in the shower or in your hairbrush.
• Thinner-feeling hair, sometimes most noticeable at the temples or parting.
• No scarring, redness or scaling of the scalp.
• Club-shaped white bulbs at the root of shed hairs, which is characteristic of telogen hairs.

Telogen effluvium rarely causes complete baldness. Many people notice a change in volume more than others do.

Other possible contributors

Hair loss during treatment is not always caused by the medicine or the weight loss. A GP may want to rule out other causes, particularly if the pattern is unusual.

Nutritional deficiencies

Eating less overall can lead to lower intake of key nutrients. Those most often linked to hair shedding include:

• Iron. Low iron stores (ferritin) are a well-known contributor, particularly in people who menstruate.
• Protein. Hair is made mainly of a protein called keratin. Very low protein intake can affect hair growth.
• Zinc, vitamin D and B12, though the evidence linking these to hair loss is more mixed.

Our guides to protein on GLP-1 treatment and vitamins and supplements on GLP-1 treatment explain how to support nutrition while appetite is reduced.

Thyroid problems

Both an underactive and an overactive thyroid can cause diffuse hair thinning. Thyroid problems are common in the general population, so they are worth checking if hair loss is significant.

Hormonal changes

Female and male pattern hair loss (androgenetic alopecia), menopause, stopping hormonal contraception and conditions such as polycystic ovary syndrome (PCOS) can all affect hair. These usually follow a different pattern to telogen effluvium, but weight loss may make an existing tendency more noticeable. See our guides to GLP-1 medication and PCOS and the menopause.

Other medical causes

Alopecia areata (patchy hair loss caused by the immune system), scalp conditions, and some other medicines can also cause hair loss. These need assessment by a GP and sometimes a dermatologist.

How long does it last?

For telogen effluvium triggered by a time-limited event, the typical course is:

These timings are typical, and individual experience varies. Shedding can continue for longer if the trigger, such as ongoing rapid weight loss or low protein intake, persists. When telogen effluvium lasts longer than six months it is sometimes called chronic telogen effluvium, and it is worth seeing a GP.

Because scalp hair grows only around a centimetre a month, it takes time for regrowth to show. Many people notice short new hairs along the hairline first.

What you can do

There is no proven way to prevent hair loss on Mounjaro, but several sensible steps may reduce the risk or support recovery. Discuss any changes to your treatment with your prescriber first.

Eat enough protein and a varied diet

When appetite is low, it is easy to fall short on protein. Prioritising protein at each meal, from foods such as eggs, fish, poultry, dairy, tofu, beans and lentils, helps support hair, skin and muscle. Our protein guide suggests practical ways to do this when portions are small. Our article on what to eat on GLP-1 medication covers a balanced approach.

Avoid very rapid weight loss where possible

Weight loss on tirzepatide is often fastest in the first months. If you are eating very little, losing weight very quickly, or struggling with side effects that stop you eating, tell your prescriber. They may consider staying on a dose for longer before increasing it. The Mounjaro SmPC sets a minimum of four weeks on each dose; your prescriber can decide whether a slower pace is appropriate. Our guide to Mounjaro doses explains the titration schedule.

Ask about blood tests

If shedding is significant, your GP may check:

• Full blood count and ferritin (iron stores).
• Thyroid function.
• Vitamin D, B12 and folate.
• Sometimes zinc or other markers depending on your history.

This helps identify a deficiency that can be corrected, rather than guessing with supplements.

Be cautious with supplements

Biotin is widely marketed for hair, but good evidence that it helps people who are not deficient is lacking. High doses of biotin can also interfere with some laboratory tests, including thyroid tests and troponin (a heart test), so tell your doctor if you take it. Iron supplements can cause constipation and stomach upset, which may add to GLP-1 side effects, and iron should be taken only if a deficiency is confirmed. A pharmacist can advise on interactions and suitable products.

Look after your hair gently

• Use a mild shampoo and avoid harsh chemical treatments while shedding is active.
• Avoid tight hairstyles that pull on the scalp.
• Limit heat styling.
• Remember that brushing and washing do not cause more hair to fall out overall; they just remove hairs that were already shedding.

Treatments for persistent hair loss

Topical minoxidil is available from pharmacies and is used for some types of hair loss. Whether it is appropriate for you depends on the cause of your hair loss and your medical history, so ask a pharmacist or GP. It is not usually needed for typical telogen effluvium, which tends to recover on its own.

Should you stop Mounjaro?

For most people, hair shedding alone is not a reason to stop treatment, especially as the SmPC reports that most cases recovered during continued treatment. However, that decision belongs to you and your prescriber.

Things your prescriber may consider include:

• How much weight you have lost, and how quickly.
• Whether you are eating enough, and whether side effects are limiting your intake.
• Whether blood tests show a deficiency.
• How much the hair loss is affecting your wellbeing and confidence.
• The overall benefits of treatment for your health.

Do not stop or skip doses on your own. If you stop and later restart, you may need to begin again at a lower dose, and stopping is often followed by weight regain. Our guides to Mounjaro maintenance and weight regain after stopping GLP-1 medication explain what the evidence shows about stopping.

Hair loss and body image

Weight loss can bring other physical changes too, such as changes in the face and loose skin. For some people, losing hair at the same time can feel distressing, even when it is temporary. It is worth talking about this with your prescriber or GP, particularly if it is affecting your mood. Our guide to facial changes and loose skin and our article on GLP-1 medication and mental health may help.

How Mounjaro compares with other weight-loss medicines

Hair loss is listed as a common side effect for semaglutide (Wegovy) as well. The UK Wegovy leaflet notes that it occurs more frequently with the higher 7.2mg dose. In STEP 1, around 3% of people on semaglutide 2.4mg reported hair loss compared with about 1% on placebo.

Because the trials were run separately, it is not possible to say for certain whether one medicine causes more hair loss than the other. Greater average weight loss with tirzepatide in SURMOUNT-1 may partly explain the slightly higher figure. For a broader comparison, see Mounjaro vs Wegovy and our Wegovy side effects guide.

If you are comparing regulated services, it may be worth checking what follow-up support each offers if side effects arise. Our provider comparison sets out how services differ, and our prices page explains what affects overall cost, including whether follow-up consultations are included.

When to speak to a professional

Talk to your prescriber, GP or pharmacist if:

• Hair shedding is heavy or worrying you.
• Shedding continues for more than about six months.
• You are losing weight very quickly or struggling to eat enough.
• You have other symptoms that could suggest a deficiency or thyroid problem, such as extreme tiredness, feeling cold, palpitations, breathlessness, brittle nails or pale skin.
• You want to start a supplement or a hair treatment.

See a GP promptly if:

• Hair loss is patchy, with distinct bald areas.
• Your scalp is red, scaly, painful, itchy or scarred.
• You have hair loss on other parts of the body, such as eyebrows or eyelashes.
• Hair loss started suddenly with no obvious trigger.

Get urgent medical help (NHS 111, or 999 / A&E in an emergency) if, while taking Mounjaro, you develop:

• Severe, persistent abdominal pain, possibly spreading to your back, with or without vomiting.
• Signs of dehydration that do not improve, such as dizziness, confusion or passing very little urine.
• Signs of a serious allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing.

Your prescriber is the right person to weigh your side effects against the benefits of treatment and decide on any changes.