Mounjaro and hair loss: what is known

Yes, hair loss is an effect described with Mounjaro (tirzepatide) and with other weight-loss pens. In the main clinical trials, about 5% of people treated with tirzepatide reported hair loss, compared with about 1% of those who received placebo. In clinical practice, the figures are similar and hair loss seems to be more common in women.

In most cases, it is not the medicine attacking the hair directly. Rapid weight loss, lower food intake and a lack of protein trigger a diffuse, temporary hair loss called telogen effluvium, the same as happens after bariatric surgery or a very restrictive diet. As a rule, it is reversible.

In this guide we explain what studies say, why it happens, how long it lasts, how to reduce the risk and when an assessment is worthwhile. One important rule from the start: do not stop the treatment on your own. Talk first to the doctor who prescribed it.

What Mounjaro and the other "pens" are

So-called weight-loss pens are injectable medicines that mimic hormones produced by the gut after meals. They reduce appetite, increase the feeling of fullness and slow down stomach emptying. They are used in the treatment of type 2 diabetes and obesity.

These are prescription-only medicines. In clinical trials in obesity, tirzepatide led to average weight losses of about 15% to 21% after around a year and a half, depending on the dose. It is precisely this rapid and significant weight loss that underlies most cases of hair loss.

What the studies say

Clinical trials with tirzepatide (SURMOUNT programme)

Source: Eli Lilly, medical information on the SURMOUNT trials.

In the type 2 diabetes trials (the SURPASS programme), in which weight loss is smaller, hair loss was far less common: 13 in 5,119 participants, or 0.25%. The manufacturer states that, in the weight-management trials, hair loss was associated with significant weight loss and may be transient.

Real-life studies

• GLP-1 in general. A study of almost 548,000 users of GLP-1 medicines, compared with the same number of people not taking them, found after 12 months a 40% higher risk of non-scarring hair loss. The risk of telogen effluvium was 76% higher, and that of diagnosed androgenetic alopecia 64% higher. Alopecia areata did not increase (Akiska et al., 2025).
• Tirzepatide vs. semaglutide. A 2026 study compared about 12,900 people in each group. After one year, hair loss appeared in 4.2% with tirzepatide and 2.9% with semaglutide. Even when comparing people with the same weight loss, the difference remained (4.2% vs. 3.3%). In women, the figures were 5.4% and 3.6% (Marwaha et al., 2026).

How to read these numbers

• Hair loss is a frequent but not universal effect: the great majority of people treated do not report it.
• It is clearly linked to the amount of weight lost, but weight loss may not explain everything, especially with tirzepatide.
• The rise in diagnoses of androgenetic alopecia may reflect a predisposition that becomes visible with the effluvium, and not necessarily a new condition.
• These are observational studies, which show associations and do not prove causation. The 2026 study does not yet have an identified journal publication.

Why it happens

The main mechanism: telogen effluvium

Hair has a cycle: about 85% to 90% of hairs are growing and 10% to 15% resting. When the body goes through a "shock", such as rapid weight loss, surgery, an illness or childbirth, many hairs move into the resting phase at the same time and fall out 2 to 4 months later. This is telogen effluvium.

With weight-loss pens, several factors may add up:

• Rapid and significant weight loss. The body interprets it as a period of scarcity and saves resources on non-essential structures, such as hair.
• Eating far less. Reduced appetite is the aim of the treatment, but it can lower protein, iron, zinc and other vitamins too far.
• Nausea and vomiting, especially at the start and when the dose is increased, which reduce food intake even further.
• Dehydration and tiredness, which add to the body's stress.

The 2025 joint recommendation of several North American nutrition and obesity societies lists hair loss as one of the possible consequences of insufficient intake of protein, vitamins and minerals during treatment with these medicines (Mozaffarian et al., 2025).

The comparison with bariatric surgery

Hair loss after obesity surgery is well known and helps to explain what happens with weight-loss pens. A meta-analysis of 18 studies found hair loss in 57% of those operated on, more common in the first year and in younger people. Those with hair loss had, on average, lower zinc, ferritin and folic acid (Global Bariatric Research Collaborative, 2021). Hair loss usually begins 3 to 4 months after surgery, lasts on average 5 to 6 months and does not leave permanent baldness (Smolarczyk et al., 2024).

Weight-loss pens cause weight loss that is usually slower than surgery, which helps to explain why hair loss is less common.

Could there be an effect of the medicine itself?

It is not yet known. The fact that tirzepatide has more hair loss than semaglutide even with similar weight loss suggests there may be other factors, but studies do not yet explain the mechanism. The receptors for these hormones exist in several tissues, and research continues.

When hair loss reveals something else

Effluvium can make visible an androgenetic alopecia that was starting, especially in women with a family history or at the menopause. Obesity and polycystic ovary syndrome, common in those having these treatments, are also associated with this type of hair loss. In these cases, hair loss does not fully recover on its own and may benefit from treatment.

When it starts, how long it lasts and whether it recovers

In telogen effluvium, the follicles are not destroyed. That is why hair loss is, as a rule, reversible. The first signs of recovery are short, spiky hairs along the front hairline and on top.

If hair loss goes on beyond 6 months, if the hair becomes thinner in a specific area or if there is no regrowth, an assessment is important: there may be a deficiency to correct or an associated androgenetic alopecia.

How to reduce the risk and intensity of hair loss

1. Protein at every meal

This is the most important point. With a reduced appetite, protein tends to be the first thing to fall short. Start each meal with the protein and only then the accompaniments.

• Good sources: fish, chicken, turkey, eggs, Greek yoghurt or skyr, fresh cheese, pulses, tofu.
• When you are not hungry: small, frequent portions, high-protein yoghurts, boiled eggs, soups with pulses or shredded fish.
• The right amount depends on your weight, age and physical activity; it should be set with the doctor or dietitian overseeing the treatment.

More details in Losing weight without losing hair: protein and nutrients.

2. Monitor micronutrients

The 2025 joint recommendation highlights iron, vitamin D and calcium as nutrients to watch and, when necessary, supplement during treatment (Mozaffarian et al., 2025). Zinc, vitamin B12 and folic acid also deserve attention, especially if you have had bariatric surgery or take metformin.

A simple multivitamin may be useful while you are eating little, but avoid "hair" supplements with high doses of vitamin A, selenium or biotin: excess can even cause hair loss, and biotin distorts blood tests.

3. A sustainable pace of weight loss

The dose is increased gradually for a reason: to give the body time to adapt. Following the doctor's schedule, without speeding up on your own, and reporting persistent nausea or vomiting helps to avoid periods when you hardly eat.

4. Strength training

Strength training, two to three times a week, helps to preserve muscle mass during weight loss and is recommended during these treatments. A healthier body composition also benefits the body as a whole.

5. Blood tests before and during treatment

Having blood tests at the start and a few months later makes it possible to detect deficiencies before the hair reveals them:

• full blood count and ferritin;
• vitamin D;
• vitamin B12 and folic acid;
• zinc, in selected cases;
• thyroid function, if there is significant hair loss or other symptoms.

Find out what to ask for in Blood tests for hair loss: what to ask for.

6. Look after your hair gently

While hair loss is active: loose hairstyles, less heat from hairdryers and straighteners, a gentle shampoo and a cut that gives volume. Washing does not increase hair loss; it only releases hairs that were already going to fall.

Should I stop the treatment?

In most cases, it is not necessary. Hair loss from effluvium is temporary and the health benefits of treatment, when properly indicated, are important. Stopping suddenly also does not halt the hair loss that has already begun, because the hairs that will fall out entered the resting phase months earlier.

The decision should always be made with the doctor who prescribed the medicine. Together, you can assess:

• adjust the dose or the pace of increase;
• boost your diet and correct deficiencies;
• refer to a nutrition consultation;
• treat the hair loss in parallel, when there is an associated androgenetic alopecia.

Other causes to rule out

Not all hair loss that appears during treatment is caused by it. It is worth ruling out:

• thyroid problems;
• iron deficiency, especially in women with heavy periods;
• other medicines started at the same time;
• stress, recent illness, surgery;
• hormonal changes, such as the menopause or polycystic ovary syndrome;
• previous androgenetic alopecia.

A note on products bought without a prescription: pens bought outside the pharmacy channel, without a prescription or of doubtful origin may not contain what they claim and carry serious health risks. Use only medicines that are prescribed and dispensed in a pharmacy.

When to seek a medical assessment

At Luxmed, the Hair Medicine consultation assesses the cause of hair loss with trichoscopy and, when indicated, blood tests, and liaises with the doctor overseeing your obesity or diabetes treatment.

This article is for information only and does not replace follow-up with your doctor. Do not change or stop any medicine without medical advice.

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