Mounjaro, Wegovy and hair loss: is it the jab or the weight loss?

Hair loss is a listed side effect of both Mounjaro and Wegovy, and the usual explanation is that it's the weight loss, not the medicine. A UK pharmacist goes through how sure anyone can actually be, and what to do if your hair is shedding..

The good news is that it changes less than you'd think about what to do. Stopping your injection won't bring back hair that's already shedding, and in the trials most people's hair recovered while they stayed on treatment. ^[1][2]

If you're taking Mounjaro or Wegovy and finding more hair in the shower or on your brush, you're not imagining it, and for most people it isn't permanent. Hair loss is listed as a common side effect of both medicines in their UK product information, which means it affects between 1 in 100 and 1 in 10 people taking them. ^[1][2]

It's most likely a temporary type of shedding called telogen effluvium, which tends to start a few months after a big change in the body, such as losing weight quickly. ^[3][4] The usual explanation is that it's the weight loss, not the jab. That's probably mostly right, but nobody has measured how much of it the weight loss explains, and one study from this year suggests it may not be all of it.

The UK labels take their figures from the trials the medicines were licensed on. Across three Mounjaro weight loss trials, 4.9% of people taking it reported hair loss, against 1.0% of people on a dummy injection, or placebo. ^[1] Across the four main Wegovy trials, which ran for 68 weeks, it was 2.5% on the standard 2.4mg dose against 1.0% on placebo. ^[2]

So out of every 100 people on Mounjaro in those trials, about 5 reported hair loss, against 1 on placebo. On Wegovy 2.4mg it was 2 or 3 in every 100.

Both labels say the hair loss was mainly mild and that most people recovered while staying on treatment. ^[1][2] In the Mounjaro trials, nobody stopped taking it because of hair loss. ^[1]

Two things are worth knowing about these numbers. The trials were run and paid for by the manufacturers: Eli Lilly for Mounjaro and Novo Nordisk for Wegovy. ^[5][6] And they weren't set up to look at hair. Hair loss was counted when it was reported as a side effect rather than measured, so milder shedding may have gone unrecorded. ^[4]

Most of it was reported by women. In the tirzepatide weight loss trials, hair loss was reported by 7.1% of women against 0.5% of men, and in the Wegovy 7.2mg trials by 8.4% of women against 0.2% of men. ^[7][8] It isn't currently known why.

At any one time, most of the hair on your head is growing. Normally only about 15% is in the resting phase before it falls out, but in telogen effluvium a shock to the body pushes that up to 30% or more. ^[3]

Those hairs don't fall out straight away. Shedding usually starts around 3 months after whatever triggered it, and it tends to begin suddenly, which is why it can seem to come out of nowhere. ^[3] Marked weight loss and extreme dieting are recognised triggers, along with illness, surgery, childbirth, stressful events and starting new medicines. ^[3] So is a sudden drop in how much protein you eat. ^[9]

The hair comes out from all over the scalp rather than in patches. The shedding phase usually lasts 3 to 6 months, and then new hair starts to grow, although it can take many more months for your hair to get back to its normal thickness. ^[3]

That fits with the largest study so far, the extra hair loss it found with these medicines was mainly the non-scarring kind, where the follicles aren't destroyed, and there was no clear link with alopecia areata, the patchy autoimmune type. ^[4]

Our guide to the different types of hair loss goes through telogen effluvium in more detail, including how to tell it apart from other types.

The usual answer is that it's the weight loss, not the medicine causing the hair loss.

The case for the weight loss

Losing weight quickly causes hair shedding on its own, with no medicine involved. ^[3][9] The clearest example is weight loss surgery. A 2021 review that pooled 18 studies of more than 2,500 people found 57% reported hair loss after surgery, although the figure varied hugely from study to study. ^[10] A larger 2025 update, pooling 41 studies of more than 7,000 people, put it at 47%. ^[11] In the 2021 review, hair loss was more common in younger people and in those with low folic acid or low ferritin, a measure of iron stores. ^[10]

The Wegovy SPC says hair loss was reported more often in people who lost 20% or more of their body weight, and tirzepatide says hair loss was associated with weight reduction. ^[2][7]

Another case that points it towards being the weight loss rather than the jab is depsite being the same active ingredient (semaglutide) hair loss isn't listed as a side effect of Ozempic, which uses lower doses for type 2 diabetes.

The most direct evidence comes from Wegovy's higher dose. When the European Medicines Agency reviewed the 7.2mg trials, it found hair loss was linked with weight loss. On 7.2mg, it was reported by 9.0% of people who lost 20% or more of their weight, against 4.1% of people on the same dose who lost less. ^[13]

Because everyone in that comparison was on the same dose, it gets closer to separating the weight loss from the medicine. It still isn't proof, as the people who lose the most weight may differ from the rest in other ways.

A study published in the BMJ in July 2026, used the health records of about 12,000 US adults with type 2 diabetes who started a GLP-1 medicine, a group that in this study included semaglutide and tirzepatide, and compared them with people starting two other types of diabetes medicine. ^[4] It was paid for by the US National Institutes of Health rather than a drug company. ^[4]

After adjusting for differences between the groups, people starting a GLP-1 medicine were 37% more likely to be diagnosed with hair loss than people starting an SGLT-2 inhibitor, and 68% more likely than people starting a DPP-4 inhibitor. Those percentages sound big, but they’re increases on very small numbers. Each year, about 5 in every 1,000 people on SGLT-2 inhibitors were diagnosed with hair loss, and about 4 in every 1,000 on DPP-4 inhibitors. So in real world terms, that’s 2 or 3 extra people in every 1,000 each year. ^[4]

Diagnoses were concentrated in the first year of treatment, and the authors think weight loss and eating less are the most likely explanation. ^[4]

Where it gets less certain

The BMJ study didn't test how much of the extra hair loss was down to weight loss, and the authors say that still needs working out. ^[4] It's also an observational study rather than a trial, everyone in it had type 2 diabetes, and it only counted hair loss that a doctor had diagnosed and recorded. ^[4]

In the main Mounjaro trial, hair loss was reported about as often on the lowest dose as on the highest, 5.1% against 5.7%, even though people on the highest dose lost more weight where we would expect the one who lost the most to experience the most hair loss. ^[5] Though everyone in that trial lost a lot of weight, so it may not mean much.

One study has tried to separate the two. Posted online in July 2026, it compared about 11,000 people starting tirzepatide with the same number starting semaglutide, matched on roughly how much weight they'd lost. ^[14] If weight loss were the whole story, people who lost similar amounts should have had a similar risk. Within a year, 4.2% of the tirzepatide group had hair loss recorded, against 3.3% on semaglutide, so there was a slight difference reported between the two drugs despite the weight loss amount being the same. ^[14]

But that same study also backs up the weight loss explanation. On both medicines, recorded hair loss rose steadily with the amount of weight lost. And the authors found no sign of the receptors these medicines act on in the skin cells of the hair follicle, which makes a direct effect on the follicle less likely. ^[14]

But it's a preprint, which means other scientists haven't checked it through peer review yet. All four authors are from nference, the health data company whose patient records it used. It matched people on broad bands of weight loss rather than exact amounts, and it picked up hair loss from diagnosis codes and doctors' notes. ^[14]

So which is it?

Weight loss is the most likely main cause, and the extra hair loss seen so far is mostly the temporary, non-scarring kind. But nobody has measured how much of it the weight loss explains, and one unreviewed study suggests it may not be all of it.

So "it's just the weight loss" is a reasonable best guess, not a proven fact. The reassuring part is that what you should do doesn't change either way.

Hair loss was reported about twice as often with Mounjaro as with Wegovy 2.4mg, 4.9% against 2.5%. ^[1][2] But those numbers come from different trials with different people, and Mounjaro produced more weight loss in its trials. Setting separate trials side by side is a weak way to compare two medicines, as we explain in our Wegovy vs Mounjaro guide.

The only trial to give people the two medicines side by side was SURMOUNT-5, which was funded by Eli Lilly. Hair loss was reported by 8.3% of people on Mounjaro and 6.1% on Wegovy, but the Mounjaro group also lost more weight, 20.2% against 13.7% on average. ^[15] With 54 cases across both groups, a gap that size could easily be down to chance.

The unreviewed study above found a little more hair loss on tirzepatide, even in people who'd lost similar amounts of weight. ^[14]

So Mounjaro may carry a slightly higher risk, but it hasn't been shown in a trial. Hair loss on its own isn't a reason to switch. Which medicine suits you is a decision for you and your prescriber, based on everything else as well.

Probably not and definitely not without speaking to your provider first. Telogen effluvium shows up around 3 months after its trigger, so the shedding you're seeing now was set in motion months ago. ^[3] Stopping today won't bring those hairs back. In the trials, most people's hair recovered while they stayed on treatment, and nobody on Mounjaro stopped because of it. ^[1][2]

Stopping has effects of its own too. In trials where people were switched from the medicine to a dummy injection, much of the weight they'd lost came back within a year. ^[1][2]

If you're worried, or the shedding is getting you down, talk it through with your prescriber before you change anything. Do not lower your dose or skip injections on your own.

For most people, all they need is time. Telogen effluvium usually gets completely better on its own, and taking medication doesn't speed up the regrowth. ^[3] In a Korean study that looked back at the records of 140 people whose shedding followed weight loss, every one of them improved without treatment, after about 5 months on average. ^[16]

Make sure you're still eating enough.

These medicines cut your appetite, which is how they work, but it's easy to end up eating very little. The British Dietetic Association's guide for people on them suggests having protein rich foods at each of your three meals, and warns that not eating enough can leave you dizzy, tired, low and losing hair. ^[17] If you're worried you're not getting enough, your prescriber or a dietitian can help. ^[17] The guide was part-funded by Novo Nordisk and Eli Lilly, who the BDA says had no input into its content. ^[18]

Don't add a crash diet on top.

The medicine is already reducing how much you eat. Cutting back hard on top of it adds more of the thing that sets off shedding in the first place: rapid weight loss and eating much less. ^[3][9] If the weight is coming off very fast, or you're struggling to eat at all, tell your prescriber.

Get your bloods checked if there's a reason to.

If the shedding hasn't settled after 6 months, or you have other symptoms, your GP may suggest a blood test to rule out other causes, such as thyroid problems or low iron. ^[3] Low iron is worth sorting out, because telogen effluvium can come back if it's left untreated. ^[3]

Save your money on hair supplements.

No trials have shown that biotin helps hair loss unless you're actually low in it, and there's little evidence for most other hair supplements either. ^[9] Some can do harm in large amounts: too much vitamin A or selenium can cause hair loss itself. ^[9] Biotin can also give falsely high or low results on some blood tests, including thyroid tests, and it's in a lot of hair, skin and nails products. ^[19][20] If you take it, tell your GP before any blood test.

We prescribe hair loss treatments, and this is still the kind of shedding we'd rather you waited out than spent money on.

Some of what you're seeing may not be down to the medicine at all. Telogen effluvium can unmask pattern hair loss that was already on its way. ^[21] When a lot of hair sheds at once, thinning at the temples, crown or parting that you hadn't noticed can suddenly look obvious.

How your hair loss is progressing is a clue on what you may be suffering with. Telogen effluvium thins hair all over the scalp. Pattern hair loss is concentrated at the temples and crown in men, and along the parting in women, and it carries on gradually after the shedding has settled.

Shedding has other causes too, including thyroid problems, low iron, illness and coming off the contraceptive pill. ^[3] Patchy bald areas, a sore or scaly scalp, or losing your eyebrows point to something else altogether and need seeing by a GP.

If you were already using finasteride or minoxidil for pattern hair loss before you started, a bout of shedding doesn't mean they've stopped working.

Neither is a treatment for telogen effluvium, which normally gets better without one. ^[3] Finasteride is licensed for men with male pattern hair loss, and not for women. ^[22] It works by lowering DHT, the hormone behind pattern hair loss, which isn't what drives shedding after weight loss.

If pattern hair loss is showing through, that's a separate question, and treatment can help. Our guide to using minoxidil and finasteride together goes through how much each one adds.

Quite a lot, considering how many people take these medicines.

• No trial has been designed to answer this question, and the licensing trials only recorded hair loss when people reported it. ^[4]
• The largest study only included people with type 2 diabetes, only counted hair loss that a doctor diagnosed, and came from one US health system. ^[4]
• The same study found more scarring hair loss compared with DPP-4 inhibitors, but not compared with SGLT-2 inhibitors, which is hard to read either way. ^[4]
• The study pointing to something beyond weight loss hasn't been peer reviewed, and its authors are from the company whose data it used. ^[14]
• Nobody has tested whether losing weight more slowly, or eating more protein, lowers the risk.
• And nobody has measured how much of the hair loss the weight loss explains, which is the question this whole article turns on.

Most shedding on these medicines settles by itself. Arrange to see your GP, or speak to your prescriber, if any of the following apply:

1. The shedding has gone on for more than 6 months, rather than settling.
2. You have one or more bald patches, rather than thinning all over.
3. Your scalp is red, scaly, sore or burning, or looks smooth and shiny.
4. You're also losing hair from your eyebrows, eyelashes or body.
5. You have other new symptoms, such as tiredness or changes to your periods.
6. You're struggling to eat or drink, or you're being sick often.
7. The hair loss is affecting your mood or how you feel about yourself.

Seek urgent medical attention for severe and persistent abdominal pain, particularly if it spreads through to the back or is accompanied by vomiting. ^[1][2] If you have swelling of your face, lips, tongue or throat, or difficulty breathing, call 999. ^[1][2]