Mounjaro (Tirzepatide) – Weight Loss Benefits, NHS & NICE Guidance
Managing obesity is a growing challenge in the UK. According to the NHS, lifestyle changes such as a balanced diet and regular physical activity remain the foundation of weight management[1], yet many people still struggle to achieve clinically significant weight loss. Newer pharmacological options can offer support to those with severe obesity and related health conditions. One of the most talked‑about drugs is Mounjaro, the brand name for tirzepatide. This article provides an in‑depth, evidence‑based overview of how Mounjaro works, the benefits seen in clinical trials, and the regulatory guidance governing its use in the UK.
What Is Mounjaro?
Mounjaro (tirzepatide) is a dual‑incretin medicine: it activates both the glucagon‑like peptide‑1 (GLP‑1) and glucose‑dependent insulinotropic polypeptide (GIP) receptors. These incretin hormones are normally released from the gut after eating. They stimulate insulin secretion, suppress glucagon release, slow stomach emptying and reduce appetite. Diabetes UK explains that tirzepatide works by raising levels of these hormones, helping the body produce more insulin when needed and reducing appetite[2]. Because it targets two receptors, tirzepatide may produce greater metabolic and weight‑loss effects than GLP‑1‑only medicines such as semaglutide (Wegovy). Clinical trials have shown that people taking tirzepatide lose substantially more weight than those taking semaglutide[3]. It is administered as a once‑weekly subcutaneous injection[4].
Originally developed to improve blood‑sugar control in adults with type 2 diabetes, tirzepatide is now licensed for weight management. Diabetes UK notes that Mounjaro is used for type 2 diabetes when three other glucose‑lowering medicines have not been effective, and it is considered for weight loss in adults with obesity when other approaches have failed[5]. In December 2024, the National Institute for Health and Care Excellence (NICE) recommended tirzepatide for managing overweight and obesity in specific circumstances[6]. This dual approval means Mounjaro may be prescribed for diabetes, obesity or both, provided patients meet the eligibility criteria outlined by NICE and the NHS.
How Mounjaro Helps with Weight Loss
Tirzepatide’s dual‑receptor action makes it one of the most potent pharmacological tools currently available for weight management. MedCare Health Clinic’s overview of the drug reports that clinical studies have shown up to 22 % total body‑weight reduction in participants[7], significantly more than the average 15 % reduction seen with semaglutide[8]. This dramatic effect stems from several mechanisms:
- Appetite suppression and satiety: By stimulating both GLP‑1 and GIP receptors, tirzepatide reduces hunger signals and increases feelings of fullness after meals, helping people naturally decrease their caloric intake[2]. The dual action may counteract the body’s natural compensatory mechanisms that often limit long‑term weight loss with diet alone.
- Improved glucose and lipid metabolism: Mounjaro enhances insulin secretion when blood sugar levels are high and suppresses glucagon when levels are normal. Diabetes UK notes that this helps improve insulin sensitivity and control blood sugar[5], which can indirectly support weight loss by reducing insulin resistance–related hunger. NICE’s technology appraisal concluded that tirzepatide with diet and exercise support is more effective at improving metabolic health than diet and exercise alone or even semaglutide[3].
- Slower gastric emptying: Like other GLP‑1 medicines, tirzepatide slows how quickly food leaves the stomach, prolonging satiety and stabilising blood‑glucose levels. This helps people avoid the spikes and dips in blood sugar that can trigger cravings.
- Dual benefit for people with diabetes: For adults with type 2 diabetes, Mounjaro offers glycaemic control and weight reduction. Stable blood sugar can make weight management easier by preventing hypoglycaemia‑driven overeating and reducing the need for insulin or other medications that contribute to weight gain.[9]
Clinical Evidence and UK Regulatory Guidance
NICE Recommendations
In December 2024, NICE issued technology appraisal TA1026, making tirzepatide the first dual‑incretin medicine approved for weight management on the NHS. The guidance recommends Mounjaro “alongside a reduced‑calorie diet and increased physical activity” for adults with an initial body‑mass index (BMI) of at least 35 kg/m² and at least one weight‑related comorbidity[6]. People from South Asian, Chinese, other Asian, Middle Eastern, Black African or African‑Caribbean backgrounds may qualify at a BMI 2.5 kg/m² lower because these groups face higher health risks at lower BMIs[6]. NICE emphasises that tirzepatide should be used when diet and exercise alone have not achieved adequate weight loss, and that treatment should be reassessed if less than 5 % of initial weight has been lost after six months on the maximum tolerated dose[10].
NICE clarifies that the drug should not be prescribed solely for people with a BMI between 30 kg/m² and 35 kg/m² unless they fall into the higher‑risk ethnic‑adjusted categories, because cost‑effectiveness estimates for this group exceed accepted thresholds[11]. It also states that tirzepatide must only be used as part of a comprehensive weight‑management programme that includes dietary and behavioural support[6].
NHS England Implementation
The NHS England weight management injections page provides details on how tirzepatide will be implemented within the health service. From 23 March 2025, tirzepatide may be prescribed for weight management only through specialist weight‑management services, where multidisciplinary teams can provide dietary counselling and behavioural support[12]. Initially, due to limited resources, the NHS is prioritising people with the highest clinical need. These include adults with a BMI of 40 kg/m² or more and at least four weight‑related conditions such as dyslipidaemia, hypertension, obstructive sleep apnoea, cardiovascular disease or type 2 diabetes[13]. Over the first three years, the programme will expand, but primary‑care prescribing will remain limited until sufficient specialist capacity exists[14].
In primary care, GPs may prescribe tirzepatide only if strict criteria are met, and patients will be reviewed after six months to confirm they have lost at least 5 % of their body weight[15]. Patients must also be counselled on contraceptive use: the NHS warns that tirzepatide may impair oral contraceptive absorption, so women should use condoms during the first four weeks of treatment and for four weeks after each dose increase[16]. Similar caution applies to hormone replacement therapy (HRT); patches or gels are recommended over oral tablets[17]. Tirzepatide is not recommended during pregnancy or breastfeeding[18].
Clinical Trial Outcomes
Phase III SURMOUNT trials evaluated tirzepatide for obesity without diabetes and reported average weight‑loss reductions of 15 % to 22 % after 72 weeks, depending on the dose. These trials compared tirzepatide to placebo and to semaglutide 1 mg; tirzepatide consistently produced greater weight‑loss and metabolic improvements. While the published NICE guidance summarises these findings, it is important to emphasise that the drug’s long‑term safety and effectiveness beyond two years remain under investigation, and weight regain can occur when treatment stops. Therefore, Mounjaro should be integrated into a holistic plan that includes lifestyle modifications and ongoing support.
Who Can Take Mounjaro?
Eligibility Criteria
According to Diabetes UK, adults over 18 with type 2 diabetes may be prescribed Mounjaro when three other medicines have failed to provide adequate control or cannot be tolerated[19]. For weight management, NICE and NHS guidelines require that patients have BMI ≥ 35 kg/m² with at least one weight‑related condition or BMI ≥ 30 kg/m² (or lower for certain ethnic groups) if weight‑related health problems warrant treatment[6][20]. NHS England’s interim commissioning plan further prioritises those with BMI ≥ 40 kg/m² and four or more weight‑related conditions for early access[21].
Ethnic Adjustments
Because people from Black African, African‑Caribbean, South Asian, Chinese and Middle Eastern backgrounds develop weight‑related conditions at lower BMI levels, NICE recommends reducing BMI thresholds by 2.5 kg/m² for these groups[22][23]. This means that someone of South Asian heritage with a BMI of 32.5 kg/m² and type 2 diabetes may qualify for tirzepatide. Such adjustments help address health inequalities and ensure that high‑risk individuals receive timely treatment.
Who Should Not Take It?
Tirzepatide is not recommended during pregnancy, breastfeeding or in people planning pregnancy[18]. Patients must also disclose all medications to their prescriber because interactions with insulin or sulfonylureas can increase the risk of hypoglycaemia[24]. People with severe gastrointestinal disease, pancreatitis, or gallbladder problems should exercise caution. Because tirzepatide slows gastric emptying, it may affect absorption of oral medications, including contraceptives and HRT[25].
Mechanism Compared with Wegovy and Other Medicines
Mounjaro stands out from other weight‑loss injections because it targets two hormones rather than one. Wegovy (semaglutide) is a GLP‑1 receptor agonist. Both drugs are administered once a week, but tirzepatide’s dual mechanism results in greater average weight loss (up to 22 % vs ~15 % with semaglutide)[8]. It may also provide superior blood‑sugar control[3]. However, Wegovy remains an effective option, particularly for patients who may not meet the stricter NHS criteria for tirzepatide[26]. Orlistat, by contrast, works in the gut by blocking fat absorption; it is available over‑the‑counter at lower doses and by prescription at higher doses. The NHS explains that orlistat is usually prescribed when lifestyle changes alone have not worked, for people with BMI ≥ 30 kg/m² or BMI ≥ 28 kg/m² with weight‑related conditions[27]. Orlistat’s common side effects include oily stools and urgent bowel movements[28], and treatment should be stopped if less than 5 % weight loss is achieved after three months[29].
Liraglutide (Saxenda) and semaglutide (Wegovy) share similar eligibility thresholds to tirzepatide, but they act solely through GLP‑1. The NHS notes that semaglutide is currently prescribed only through specialist services like medcare health clinic and pharmacy, with restrictions on BMI and health conditions similar to those for tirzepatide[30]. Weight loss medicines should always accompany a reduced‑calorie diet and increased physical activity[31].
Accessing Mounjaro in the UK: NHS vs Private Options
The rollout of tirzepatide on the NHS is gradual. The NHS England plan emphasises that, initially, only people with the highest clinical need will be eligible[21]. GPs will need to refer patients to specialist weight‑management services for assessment. After March 2025, some integrated care boards may pilot direct GP prescribing for those who meet strict criteria, but numbers will remain limited[32]. Patients considering tirzepatide should discuss eligibility with their GP or check their local integrated care board’s guidance[33].
For those who do not qualify for NHS treatment or who wish to start sooner, private clinics, including MedCare Health Clinic & Pharmacy, can provide tirzepatide after a thorough assessment. Patients still need to meet safety criteria and undergo medical screening. Private treatment allows more flexibility in BMI thresholds and may be suitable for individuals with moderate obesity who have not responded to lifestyle interventions. Costs vary depending on dose and supply; NICE notes that a four‑week supply costs between £92 and £122 depending on dose strength[34]. Private packages may include consultations, injection training, ongoing monitoring and lifestyle support. Regardless of how you access Mounjaro, it is essential to combine the injection with sustained changes to diet and activity levels.
Safety and Side Effects
All medicines carry risks. Diabetes UK lists nausea, indigestion, constipation and diarrhoea as common side effects of Mounjaro[35]. There is also a risk of low blood sugar when tirzepatide is taken with insulin or sulfonylureas[36], and a potential risk of high blood sugar if insulin doses are reduced too quickly[37]. Side effects often diminish over time, but any persistent or severe symptoms should be reported to a healthcare professional or via the Medicines and Healthcare products Regulatory Agency (MHRA) Yellow Card Scheme[38].
Women using the oral contraceptive pill should use an additional method of contraception for the first four weeks of tirzepatide treatment and for four weeks after each dose increase, because diarrhoea can reduce pill absorption[39][16]. Similarly, those taking HRT should consider transdermal preparations rather than tablets[17]. Tirzepatide should not be used during pregnancy or breastfeeding[18]. Like other GLP‑1 drugs, tirzepatide may slow gastric emptying, so it could interact with oral medicines requiring rapid absorption.
Conclusion: A Powerful New Tool that Requires Careful Use
Mounjaro represents a significant advancement in pharmacological weight‑management. Its dual‑incretin mechanism can lead to substantial weight‑loss and metabolic improvements, potentially outperforming current GLP‑1‑only drugs[8]. However, access through the NHS is restricted to those with severe obesity and comorbidities[6][13], and patients must commit to lifestyle changes and ongoing medical supervision. Private clinics may offer more flexible access but still require thorough assessments and responsible prescribing. Side effects, while generally manageable, must be monitored, and the drug is unsuitable during pregnancy or breastfeeding[18]. Ultimately, Mounjaro should be seen not as a quick fix but as one component of a comprehensive weight‑management plan that includes a balanced diet, regular exercise and psychological support.
References
[1] [15] [16] [17] [18] [20] [25] [26] [27] [28] [29] [30] [39] Obesity – Treatment – NHS
[2] [4] [5] [9] [19] [23] [24] [35] [36] [37] [38] Mounjaro – Uses, How it Works and Side Effects | Diabetes UK
[3] [6] [10] [11] [22] [34] Tirzepatide for managing overweight and obesity
[7] [8] Mounjaro (Tirzepatide) Weight Loss – Preston Prescription
[12] [13] [14] [21] [31] [32] [33] NHS England » Weight management injections