In a previous post, we explored the class of medications known as GLP-1 receptor agonists and their growing role in medically supervised weight management. Since that post, a number of patients have been asking us about tirzepatide — the active ingredient in Mounjaro — and how it differs from earlier treatments. It is a fair and important question, and one that reflects just how quickly this area of medicine is evolving.

This post aims to explain what tirzepatide is, what the clinical evidence tells us about it, and why the distinction between different medication classes matters when thinking about weight management options. As always, our aim here is to inform — not to recommend any specific treatment. All decisions about prescription medication must be made on an individual basis following a thorough clinical assessment.

A Quick Recap: How GLP-1 Treatments Work

As we discussed previously, GLP-1 (glucagon-like peptide-1) receptor agonists work by mimicking a naturally occurring hormone involved in blood sugar regulation and appetite control. They slow gastric emptying, reduce hunger signals in the brain, and improve insulin response. In clinical trials, they produced meaningful and sustained weight loss in patients who met the criteria for their use.

Semaglutide — the active ingredient in Ozempic and Wegovy — is the most well-known GLP-1 receptor agonist and attracted widespread public attention over the past few years. However, the science has continued to advance, and tirzepatide represents the next significant development in this field.

What Is Tirzepatide — and How Is It Different?

Tirzepatide, marketed under the brand name Mounjaro, works through a dual mechanism that distinguishes it from earlier GLP-1 treatments. Where semaglutide acts on a single receptor pathway (GLP-1), tirzepatide acts on two: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). For this reason, it is sometimes described as a dual agonist or twin incretin.

GIP is another naturally occurring gut hormone that plays a role in energy metabolism, fat storage, and insulin secretion. By targeting both GLP-1 and GIP receptors simultaneously, tirzepatide appears to produce a more pronounced effect on both blood sugar control and body weight than treatments acting on GLP-1 alone.

This dual action is not simply a marketing distinction — it reflects a genuinely different pharmacological mechanism, and the clinical trial data suggests that this difference translates into meaningful outcomes for patients.

What Does the Clinical Evidence Show?

Tirzepatide has been studied in a substantial clinical trial programme. The SURMOUNT trials, which evaluated tirzepatide specifically for weight management in adults with obesity, produced results that attracted significant attention within the medical community.

In the SURMOUNT-1 trial, participants without type 2 diabetes who took the highest dose of tirzepatide lost on average around 20–22% of their body weight over 72 weeks, compared to approximately 2–3% in the placebo group. This level of weight reduction is substantially greater than that seen in earlier GLP-1 trials and begins to approach the outcomes historically associated with bariatric surgery in some patients.

Alongside weight loss, the trials demonstrated improvements in a range of metabolic markers including blood pressure, cholesterol, blood sugar levels, and waist circumference. Additional trials in patients with type 2 diabetes showed similarly impressive glycaemic control alongside weight reduction.

It is worth noting, as with any emerging treatment, that long-term follow-up data continues to accumulate, and the full picture of both benefits and risks over many years is still developing. The medical community will be watching this evidence base closely.

Regulatory Approval in the UK

Tirzepatide was originally approved by the MHRA in the UK for the treatment of type 2 diabetes under the Mounjaro brand. Following the weight management trial results, it subsequently received approval for use in obesity management in adults who meet specific clinical criteria — namely a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related health condition.

As a prescription-only medication, tirzepatide can only legally be prescribed by a qualified clinician following an appropriate assessment. It is not available over the counter and should never be obtained without a proper clinical consultation.

How Does It Compare to Semaglutide?

This is the question most patients ask, and it is a reasonable one. Based on the available trial data, tirzepatide appears to produce greater average weight loss than semaglutide at their respective licensed doses. However, direct head-to-head comparisons between the two are still limited, and individual responses vary considerably.

Some important points worth understanding:

• Neither treatment works for everyone, and the degree of weight loss varies significantly between individuals
• Both require ongoing use to maintain the benefit — weight tends to return if medication is stopped without other long-term strategies in place
• The side effect profiles are broadly similar — predominantly gastrointestinal symptoms such as nausea, which typically improve as the dose is gradually increased
• The choice between treatments, if either is appropriate, depends on individual clinical factors that a doctor will assess
• Cost and availability may also be practical factors, which your clinician can discuss with you

The most important point is that the question of which treatment is most appropriate for any individual patient is a clinical one — not one that can or should be answered by online research alone.

What About Side Effects and Safety?

As with all medications, tirzepatide carries potential side effects that patients should be aware of and that a prescribing clinician will discuss fully before any treatment is initiated.

The most commonly reported side effects are gastrointestinal in nature — nausea, vomiting, diarrhoea, and constipation — and are most likely to occur during the dose escalation phase at the start of treatment. In most patients these improve over time as the body adjusts. The gradual dose titration schedule used with tirzepatide is specifically designed to minimise these effects.

There are also specific contraindications. Tirzepatide is not appropriate for patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2. It requires caution in patients with a history of pancreatitis, and is not currently recommended in pregnancy. A thorough medical history is therefore essential before prescribing.

This is another reason why proper clinical assessment — rather than online prescribing with minimal checks — is so important. Contraindications that are easily identified in a face-to-face consultation can be dangerously missed when assessment is superficial.

The Bigger Picture: Medication as Part of a Managed Programme

One of the most important messages from the clinical literature on tirzepatide — and on weight management medications more broadly — is that the best outcomes occur when medication is used as part of a structured, supervised programme rather than in isolation.

The SURMOUNT trials, for example, were conducted alongside intensive lifestyle intervention support. The question of what happens to weight loss outcomes when medication is used without that support structure is one the evidence base is still working through.

At Belfast Private GP, Dr Toner’s approach to weight management reflects this understanding. Medication — where it is clinically appropriate — is considered within the context of a broader plan that addresses lifestyle, nutrition, health monitoring, and long-term weight maintenance. The goal is not simply short-term weight loss but sustainable improvement in health.

A Note on the Online Market for These Medications

Given the level of public interest in tirzepatide and semaglutide, it is worth repeating a caution we raised in our previous post. The online market for these prescription medications has grown rapidly — and so have the risks associated with obtaining them without proper clinical oversight.

The MHRA and professional bodies including the General Medical Council have raised concerns about the proliferation of online prescribing services offering minimal clinical assessment. There have also been reports of counterfeit and falsified versions of these medications entering circulation through unregulated supply chains.

If you are considering any prescription treatment for weight management, please ensure you do so through a regulated, qualified clinician who carries out a proper assessment, knows your medical history, and provides ongoing monitoring. Your safety depends on it.

Thinking About a Weight Management Consultation?

If you have been reading about tirzepatide or other weight management treatments and wondering whether they might be relevant to your situation, the right first step is a proper consultation with a GP who has specialist knowledge in this area.

At Belfast Private GP, Dr Phil Toner holds the SCOPE certification from the World Obesity Federation — a specialist qualification in obesity medicine held by very few GPs in Northern Ireland. He offers comprehensive weight management consultations that take the time to properly understand your individual situation, assess your health risks, and discuss all appropriate options with you.

A consultation is not a commitment to any particular treatment — it is a conversation. One that could give you a much clearer picture of where you stand and what might genuinely help.

To book a weight management consultation at Belfast Private GP, contact us today. No referral is required. Appointments are typically available within days.

Frequently Asked Questions

Is Mounjaro available privately in Belfast?

Tirzepatide (Mounjaro) is a prescription-only medication. Whether it is appropriate for any individual patient depends on a clinical assessment. Belfast Private GP offers specialist weight management consultations to assess suitability and discuss options in full.

Is Mounjaro better than Ozempic for weight loss?

Clinical trial data suggests that tirzepatide produces greater average weight loss than semaglutide at their respective licensed doses. However, individual responses vary, and the question of which treatment is most appropriate — if either — is a clinical one that should be discussed with a qualified GP or specialist following a thorough assessment.

What is the difference between Mounjaro and Wegovy?

Wegovy contains semaglutide and acts on a single receptor pathway (GLP-1). Mounjaro contains tirzepatide and acts on two receptor pathways (GLP-1 and GIP), which is believed to contribute to its stronger average effect on weight loss in clinical trials. Both are prescription-only medications with their own eligibility criteria and contraindications.

How quickly does tirzepatide work?

Most patients begin to notice changes in appetite relatively early in treatment, with meaningful weight loss typically becoming apparent within the first few weeks to months. The dose is increased gradually over time according to a structured titration schedule. Results vary between individuals and are best sustained within a broader supervised programme.

Do I need a referral to discuss weight management options at Belfast Private GP?

No. You can contact Belfast Private GP directly to book a consultation with Dr Toner. No GP referral is needed.

This article is intended for informational and educational purposes only. It does not constitute medical advice, a clinical recommendation, or a promotion of any specific prescription treatment. All prescription medications must be assessed, prescribed, and monitored by a qualified clinician. If you have concerns about your weight or health, please consult your GP.