Tirzepatide (Mounjaro): How It Works, How Long It Lasts and Hair Loss

Tirzepatide (marketed in Europe as Mounjaro) is a prescription-only medicine. In the EU it is authorised for type 2 diabetes and, together with diet and physical activity, for weight management in adults with obesity (body mass index of 30 or more) or overweight (27 to under 30) with at least one weight-related condition, such as high blood pressure, abnormal blood fats, sleep apnoea or prediabetes. In this article I explain how it works, what the studies show, how it fits into a medical pathway and what to know about hair loss.

What to know first Tirzepatide is used only on prescription and under medical supervision. The most common side effects are gastrointestinal: nausea, vomiting, diarrhoea, constipation and abdominal pain; with insulin or sulphonylureas it can cause low blood sugar. It should not be bought online or used without an indication: the Italian Medicines Agency (AIFA) has reported counterfeit pens of medicines in this class.

A note before we begin. Tirzepatide is a prescription-only medicine. This article is informational and doesn’t constitute a promotion of the drug or medical advice: it can only be prescribed after a clinical assessment establishing that it’s appropriate for you.

Is tirzepatide just a weight-loss drug?

It was developed as a treatment for type 2 diabetes and is also authorised for weight management: these are its two official indications. Studies are assessing other possible uses, for example in sleep apnoea and heart failure, but at present these are not separately authorised indications.

What it is not: an aesthetic shortcut. It is a medicine with precise indications, side effects you need to know about, and the need for medical supervision over time.

How does tirzepatide (Mounjaro) work in the body?

Unlike medicines that act only on the GLP-1 receptor (such as semaglutide), tirzepatide acts on two receptors for gut hormones known as incretins.

GLP-1 receptor — GLP-1 (Glucagon-Like Peptide-1) is an incretin hormone that:

• Stimulates insulin secretion when blood sugar is high
• Reduces glucagon secretion
• Slows stomach emptying
• Increases the feeling of fullness

GIP receptor — GIP (Glucose-dependent Insulinotropic Polypeptide) helps to:

• Enhance the insulin response after meals
• Regulate fat metabolism

The overall effect is better blood sugar control and reduced appetite, which leads to eating less.

What do the studies show?

Results vary from person to person and no outcome is guaranteed: the data below describe what clinical studies have measured, not what can be promised.

• Weight. In the SURMOUNT-1 registration study, in adults with obesity or overweight without diabetes, the average weight reduction after 72 weeks was between about 15% and 21% depending on the dose, compared with about 3% with placebo, always alongside diet and physical activity.
• Blood sugar. In people with type 2 diabetes, tirzepatide lowers glycated haemoglobin (HbA1c), the measure of blood sugar control over the months.
• When treatment stops. When the medicine is discontinued, part of the weight lost tends to be regained. This is why decisions on duration and stopping should be made with the doctor, as part of a pathway.

How does tirzepatide fit into a medical pathway?

In my clinical practice tirzepatide, when it is indicated, is never a stand-alone therapy: it is one part of a complete, personalised medical pathway.

The goal is not simply weight loss — which can be achieved in many ways, often at the expense of health — but losing fat mass while preserving muscle mass, correcting any deficiencies and maintaining the result over time.

The three phases of the pathway

Phase 1 — Drug therapy, when indicated If the clinical assessment confirms the indication, the first phase involves tirzepatide alongside diet and physical activity. During this phase we monitor body composition, not just weight: the aim is to lose fat mass while preserving muscle mass, which is essential for basal metabolism.

Phase 2 — Infusion support, when the assessment justifies it Infusion therapies enter the pathway when the assessment — test results and clinical picture together — warrants them, following the same principle I apply to every infusion: measure first, supplement second.

• Correcting documented deficiencies — iron, vitamin B12, vitamin D. This is the most solid indication, and during significant weight loss deficiencies are common: they should be looked for through testing, not assumed.
• NAD+ and glutathione — the biochemical rationale is real: NAD+ is a central coenzyme in mitochondrial energy metabolism, and glutathione is the principal endogenous antioxidant. It must be said honestly, however, that human clinical data for intravenous administration is still preliminary: I assess these case by case, discussing their limits openly, never as a promise.
• What an infusion doesn’t do — it doesn’t “detoxify”: the liver and kidneys perform that function extremely efficiently, and the detox drip is a commercial simplification rather than a physiological mechanism. Without a documented deficiency, excess water-soluble vitamins are simply eliminated in the urine.

I explore this further in the dedicated page on infusion therapy.

Phase 3 — Functional nutrition and targeted supplementation Long-term success depends on adopting a sustainable, personalised way of eating. Not temporary restrictive diets, but a functional nutritional approach that accounts for individual biotype, intolerances, gut microbiome and specific metabolic needs.

How are results maintained in the long term?

One of the most important aspects of the pathway is its attention to the maintenance phase. The body tends to defend its starting weight through metabolic, hormonal and behavioural adaptations: the goal is to help keep the weight reached stable over time, including when drug therapy is reduced or stopped.

Integrated monitoring system:

Periodic body composition assessments — advanced multi-frequency bioimpedance is used to monitor not just weight, but the distribution of fat mass, lean mass, and total and segmental water.

Personalised biochemical analysis — complete metabolic panels every 3-6 months include: fasting and post-prandial glucose and insulin, HbA1c, advanced lipid profile, inflammatory markers (CRP, homocysteine), liver and kidney function, thyroid profile, vitamin D, B12, iron and ferritin.

Metabolic efficiency testing — metabolic flexibility is assessed through specific tests measuring the body’s capacity to use different energy substrates.

Lifestyle adaptation — the patient is guided towards sustainable habits: personalised physical activity (not exhausting, but regular and enjoyable), stress management, sleep hygiene and mindful eating techniques.

Does tirzepatide (Mounjaro) cause hair loss?

It’s one of the questions I’m asked most often since, at the end of July 2026, a study published in the British Medical Journal linked GLP-1 drugs to a higher risk of alopecia. I wrote about it for the Italian magazine Io Donna; here are the key points.

• An association, not a certainty. Studies show a higher risk of hair loss among people taking these drugs, but that doesn’t mean everyone who takes them will necessarily lose hair. The mechanisms are still being studied.
• The most common form is telogen effluvium: diffuse shedding that can appear even months after weight loss begins, especially when weight drops quickly or comes with deficiencies in protein, iron or zinc.
• In these cases the follicle isn’t destroyed. Once the cause is corrected and nutrition is stabilised, the hair cycle can resume, although recovering density takes several months.
• Before acting, it’s essential to understand what kind of hair loss it is. Blaming everything on the drug can mean other causes are missed. There are supportive treatments for the scalp, from hair fillers to platelet-derived therapies, but the evidence isn’t equivalent for all of them, and the choice depends on the diagnosis.
• Don’t stop treatment on your own. If hair loss appears during treatment, the most useful step is to talk to the doctor following you.

This is also why monitoring iron, ferritin, vitamins and body composition isn’t a detail: weight loss that preserves nutritional status removes one of the factors that can contribute to hair loss.

The full article (in Italian): Farmaci per dimagrire e caduta dei capelli: cosa succede davvero e come intervenire, Io Donna, 22 September 2026. I’ve written about hair loss more broadly, beyond medication, from seasonal shedding to post-pregnancy, in Hair Loss: When to Worry and What Actually Helps.

If you’re coming from abroad

A few practical points for international patients, because rules differ considerably between countries.

An Italian prescription is required. Tirzepatide is prescription-only in Italy. A prescription issued in another country isn’t valid here, and treatment can’t simply be “continued” on arrival: a clinical assessment is needed to establish whether it’s appropriate for you.

The assessment comes first, always. Before any prescription, medical history, current medication, blood tests and body composition are reviewed. This isn’t bureaucracy: it’s what determines whether the treatment is suitable and safe in your specific case, and there are situations in which the correct answer is that it isn’t.

Regulatory framework and indications differ by country. What is approved, and for which indication, varies between Italy, the UK and the United States — as do the brand names. If you’ve read about this drug abroad, the information may not apply here.

Follow-up requires continuity. This is a pathway with periodic monitoring, not a one-off prescription. If your stay in Italy is short, it’s worth discussing at the outset how the follow-up will be managed.

In summary

Tirzepatide is an effective medicine for the indications it is authorised for: type 2 diabetes and weight management in people with obesity, or overweight with associated conditions. It works better, and more safely, within a pathway that includes nutrition, physical activity, regular blood tests and a plan for afterwards.

That is why, when it is indicated, I include it in a long-term metabolic health strategy, where the goal is not only to lose weight but to stay healthy over time.

Tirzepatide is a prescription-only medicine: if you think it may be relevant to you, talk to your doctor. Official information on the medicine: the EMA summary for Mounjaro.