Key questions on obesity medications

In this CPD module, GP and expert in obesity and lifestyle medicine Dr Ellen Fallows answers key questions on the prescribing of medications for weight loss in patients with obesity. Complete the module on Pulse 365 today

The management of obesity has been transformed in recent years with the use of glucagon-like peptide-1 receptor agonist (GLP-1 RA) drugs semaglutide (Wegovy) and liraglutide (Saxenda), and the dual GLP-1/glucose-dependent insulinotropic polypeptide (GIP) RA tirzepatide (Mounjaro).

The prescribing of tirzepatide in NHS primary care, albeit as part of a phased roll-out, and wider prescribing of all these drugs through private providers, has shifted much more responsibility for the medical management of obesity onto GPs.

Experience and real-world evidence with these drugs are constantly evolving, including on side effects and potential interactions, while eligibility and availability varies over time and by region, presenting a challenge for GPs to keep on top of the constantly shifting focus.

Learning objectives

This module will bring you up to date and extend your knowledge of:

• Efficacy, safety profile and clinical role of oral and injectable pharmacological treatments for obesity, including orlistat and injectable GLP-1-based therapies.
• Current UK eligibility criteria for semaglutide, liraglutide and tirzepatide across England, Wales and Scotland, recognising regional variation and phased commissioning arrangements.
• Interpret forthcoming changes to tirzepatide eligibility in England, including BMI thresholds, qualifying comorbidities and the interaction between obesity and type 2 diabetes guidance.
• Identify, counsel and manage common adverse effects of GLP-1-based agents, including perioperative considerations and medication adjustments in patients with type 2 diabetes.
• Support shared decision-making regarding treatment targets, duration of therapy, discontinuation and risk of weight regain, including considerations for repeat prescribing and private-sector treatment.

1. With all the publicity around injectables, orlistat tends to be forgotten as an option. When might this be appropriate, should it be tried before resorting to injectables and how effective is it in comparison?

In practice, many people have already tried the 60mg orlistat dose as it has been available over the counter since 2009. It is easy to take and has a longer-term evidence base supporting its safety than newer weight loss medicines. 

Weight loss reported in trials of orlistat is often only 3-5% of body weight and while it is also meant to help with reduction in LDL cholesterol in real world settings it may be less effective.

People have often experienced unpleasant side effects of orlistat such as anal leakage or excessive flatulence particularly if their diet is high in fat. This may contribute to weight loss through behavioural feedback, where these unpleasant side effects lead to consumption of a low-fat diet. However, low-fat diets are not always nutritionally adequate so this may lead to insufficient healthy fat consumption (such as oily fish, nuts) and deficiencies in fat soluble vitamins (A, D, E and K).

In summary, while cheap, relatively safe and easily available, orlistat is relatively ineffective, often stopped early and has unpleasant side effects, while potentially compromising nutrition. Moreover, unlike the injectables, there is no evidence that orlistat, in the long term, provides improvements in cardiovascular disease risk, which is the number one cause of morbidity and mortality in obesity.

2. Can you provide a refresher on the current eligibility criteria for the available medications – do these differ in the devolved health systems, compared to England?

Table 1 below details guidance as of February 2026 but this is subject to updates, local Integrated Care Board (ICB) commissioning variation and availability of specialist weight management services (which is very patchy across UK) as well as the availability of medicines – there are on-going shortages of liraglutide and supply concerns over semaglutide and tirzepatide.

Table 1. Eligibility criteria for injectable weight-loss medications in obesity^1,2

How are the eligibility criteria for tirzepatide going to change in the forthcoming years in England?

NICE has laid out a gradual cohort prioritisation to last for a maximum 12 years in England.¹ Very few patients will be able to access tirzepatide until this Summer (2026) when the BMI threshold drops to over 35 with four comorbidities. From March 2027 the BMI threshold rises again to 40 but only three comorbidities are required. (See table 2 below.)

Complicated guidance created around disease labels rather than people’s real lives is sometimes resulting in inappropriate denial of a prescription to patients with type 2 diabetes to help with weight loss. Current NICE guidance for tirzepatide use in Type 2 diabetes – as recommended for use of GLP-1 RAs as a group – includes situations where theHbA1c remains above target despite trial of three agents or if these agents are contraindicated or not well tolerated. New draft guidance updates suggest that these eligibility criteria may be widened further in the very near future, and hence this situation is highly likely to change soon.3

Tip: Assess eligibility for tirzepatide first under NICE type 2 diabetes guidance; only after this consider NICE obesity guidance for people with both obesity and type 2 diabetes. The titration is slightly different for obesity with higher maintenance doses often needed to achieve weight loss. For GPs in England, remember patients can be prescribed GLP-1 medicines while on the NHS England Type 2 diabetes Paths to Remission Programme. This includes total diet replacement for 12 weeks so may be an option for people who potentially are struggling to achieve all their nutritional needs when their appetite is suppressed.  

Table 2. Planned changes in eligibility criteria for tirzepatide in England

How do the injectables compare in terms of efficacy and side effects? As eligibility rules for tirzepatide ease, are we likely to see the use of liraglutide and semaglutide decline – or are there circumstances when these would be preferred over semaglutide?

Liraglutide would not be considered a realistic choice as it currently is not available (either as Victoza for type 2 diabetes or Saxenda for weight-loss in obesity) and is far less efficacious than tirzepatide (Mounjaro) or semaglutide (Ozempic for diabetes or Wegovy for obesity).

As noted, semaglutide (Wegovy) can be considered the ‘standard of care’ as there has been much more experience with this agent, and as there is strong data to show that this medication improves cardiovascular disease, fatty liver disease and other co-morbidities of obesity. Semaglutide is now licensed to be given at up to 7.2 mg weekly for patients with obesity only, higher than the previous top dose of 2.4 mg. The 7.2 mg dose has been shown to be superior to the 2.4 mg dose.⁴

Tirzepatide has not been on the market as long as semaglutide has, but it does have superior weight loss outcomes compared to the standard 2.4 mg dose of semaglutide,⁵ though it has never been tested against the newer 7.2 mg weekly dose of semaglutide. In practice, tirzepatide seems to have similar or perhaps fewer adverse effects compared to semaglutide, despite its enhanced efficacy, and use preference is often driven by commissioning pathways and supply chain issues.

Dr Ellen Fallows is a GP with specialism in obesity, a fellow of the British Society of Lifestyle Medicine and past RCGP advisor on obesity and type 2 diabetes

References

1. NHS England. Interim commissioning guidance. Implementation of the NICE Technology Appraisal TA1026 and the NICE funding variation for tirzepatide (Mounjaro®) for the management of obesity 2024
2. NHS Scotland. Consensus statement: national criteria for the prioritisation of glucagonlike peptide-1 receptor agonists (GLP-1 RAs) and GLP-1 RA/glucosedependent insulinotropic polypeptide receptor agonists (GIP RAs) for the treatment of obesity in NHS Scotland. 2024
3. NICE. Type 2 diabetes in adults: management. Draft for consultation. August 2025
4. Wharton S et al. Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP): a randomised, controlled, phase 3b trial. Lancet Diabetes Endocrinol 2025 Nov;13(11):949-63
5. Aronne L et al. Tirzepatide as compared with semaglutide for the treatment of obesity. NEJM 2025;393:26-36