Best Prescription Weight Loss Pill in the UK

The best prescription weight loss pill depends on your individual health profile, medical history, and clinical eligibility rather than a single option suiting everyone. In the UK, several MHRA-authorised medicines are available, including GLP-1 receptor agonists such as semaglutide (Wegovy) and liraglutide (Saxenda), the dual GIP/GLP-1 agonist tirzepatide (Mounjaro), the oral GLP-1 agonist orforglipron (Foundayo), orlistat, and naltrexone/bupropion (Mysimba). Each works differently, carries distinct side effects, and has specific eligibility criteria. This guide explains how these medicines compare, how prescribers choose between them, and what to expect from treatment.

Which prescription weight loss medicines are available in the UK?

Seven MHRA-authorised prescription weight loss medicines are available in the UK, including semaglutide (Wegovy), tirzepatide (Mounjaro), liraglutide (Saxenda), orlistat, naltrexone/bupropion (Mysimba), and orforglipron (Foundayo), each with a distinct mechanism and eligibility criteria.

Several prescription weight loss medicines are currently authorised in the UK, and the right choice depends on individual health circumstances rather than a single option being universally best. The medicines available include:

• Orlistat (Xenical 120 mg capsules): a lipase inhibitor that reduces dietary fat absorption in the gut, available as a capsule taken with meals. Xenical (120 mg) is prescription-only; orlistat 60 mg (Alli) is available over the counter from a pharmacy without a prescription and is a lower-dose product.^[1]

• Semaglutide injection (Wegovy): a GLP-1 receptor agonist given as a weekly subcutaneous injection, MHRA-authorised for chronic weight management. Wegovy is available in doses up to 2.4 mg weekly, with a higher 7.2 mg strength also authorised by the MHRA.

• Oral semaglutide (Wegovy 25 mg tablets): MHRA-authorised on 11 June 2026 for chronic weight management, this is a distinct product from Rybelsus with its own licensed posology.^[4]

• Liraglutide (Saxenda): another GLP-1 receptor agonist, given as a daily subcutaneous injection.

• Tirzepatide (Mounjaro): a dual GIP and GLP-1 receptor agonist, MHRA-authorised both for type 2 diabetes and for chronic weight management, given as a weekly subcutaneous injection using a multiple-dose KwikPen.^[5][6]

• Naltrexone/bupropion (Mysimba): an oral combination tablet acting on appetite-regulating pathways in the brain.

• Orforglipron (Foundayo): an oral GLP-1 receptor agonist tablet, now holding a UK marketing authorisation for chronic weight management.

Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, where a prescriber may consider one of these options if it is clinically appropriate. Each medicine has a distinct mechanism, eligibility criteria, and safety profile, so a clinical assessment is always required before any prescription is issued.

How do doctors decide which weight loss medication is right for you?

Prescribers select a weight loss medicine based on BMI, comorbidities, contraindications, tolerability, and concurrent medications, as no single medicine is universally superior and the decision must be individualised following a clinical assessment.

Prescribers select a weight loss medicine based on a structured clinical assessment that weighs your medical history, current medications, BMI, and any weight-related health conditions. There is no single medicine that is universally superior; the decision is individualised.

Key factors a prescriber will consider include:

• BMI thresholds: NICE guidance generally recommends pharmacological treatment for adults with a BMI of 30 kg/m² or above, or 27.5 kg/m² or above in people from certain ethnic backgrounds at higher cardiometabolic risk. Eligibility thresholds and initiation requirements differ by medicine; many agents require a higher BMI threshold and initiation within a specialist weight management service, so individual NICE technology appraisals and local pathways should be consulted.

• Comorbidities: Type 2 diabetes, cardiovascular disease, or obstructive sleep apnoea may influence which medicine is most appropriate. For example, tirzepatide (Mounjaro) and semaglutide (Wegovy) have evidence in people with type 2 diabetes and cardiovascular risk.

• Contraindications and cautions: Orlistat is avoided in chronic malabsorption syndromes. UK SmPCs for GLP-1 and dual GIP/GLP-1 receptor agonists advise counselling patients on symptoms that may suggest thyroid problems, such as a neck lump or persistent hoarseness, and caution in people with a history of pancreatitis. The primary contraindication listed in UK SmPCs is hypersensitivity to the active substance or excipients.

• Tolerability: Gastrointestinal side effects are common with several of these medicines, and a prescriber will discuss which profile is most manageable for you.

• Concurrent medications: Drug interactions, particularly with oral contraceptives when starting tirzepatide, must be reviewed. The Mounjaro UK SmPC advises using an additional non-oral contraceptive method for four weeks after starting and four weeks after each dose increase.^[10]

A thorough consultation, including blood pressure measurement and a review of any existing conditions, is essential before any prescription is issued.

How much weight can you realistically lose with these medicines?

Weight loss varies by medicine and individual; clinical trials show orlistat produces modest losses of 3 to 5 kg, while tirzepatide (Mounjaro) achieved over 20 percent body weight loss at higher doses in the SURMOUNT programme under trial conditions.

The amount of weight lost with prescription medicines varies considerably between individuals and between medicines, and results are always greater when treatment is combined with dietary and lifestyle changes. Clinical trial data provide a useful guide, though individual outcomes will differ.

In clinical trials:

• Orlistat produced modest weight loss, typically in the range of 3 to 5 kg more than placebo over one year when combined with a reduced-calorie diet, based on published meta-analyses and Cochrane reviews.^[11]

• Liraglutide (Saxenda) was associated with an average weight loss of around 5 to 7 percent of body weight in the SCALE trial programme, though some participants lost considerably more.^[12][13]

• Semaglutide injection (Wegovy 2.4 mg) demonstrated substantially greater weight loss in the STEP trial programme, with participants losing on average around 15 percent of body weight over 68 weeks alongside lifestyle intervention. The higher 7.2 mg dose, studied in the STEP UP programme, showed greater weight loss than the 2.4 mg dose in Phase 3 data, though cross-trial comparisons have limitations.

• Tirzepatide (Mounjaro) showed even larger reductions in the SURMOUNT trial programme, with some participants losing over 20 percent of body weight at higher doses, though these are trial conditions and not guaranteed in routine clinical practice.

It is important to understand that these figures come from controlled research settings. In real-world use, adherence, tolerability, and lifestyle factors all influence outcomes. Weight loss typically slows after the first six months, and medicines generally need to be continued long term to maintain the benefit. Stopping treatment is often associated with weight regain. Your prescriber can help set realistic, personalised expectations based on your starting weight and health goals.

What are the side effects and safety considerations to know about?

GLP-1 and dual GIP/GLP-1 receptor agonists most commonly cause gastrointestinal effects such as nausea and diarrhoea; serious risks include acute pancreatitis and gallbladder conditions, and suspected side effects should be reported via the MHRA Yellow Card scheme.

All prescription weight loss medicines carry potential side effects, and understanding these before starting treatment supports safer use and better adherence. Side effects vary by medicine class.

GLP-1 and dual GIP/GLP-1 receptor agonists (Wegovy injection and tablets, Saxenda, Mounjaro):

• Nausea, vomiting, diarrhoea, and constipation are the most commonly reported effects, particularly during dose escalation.

• Acute pancreatitis has been reported, including post-marketing reports of necrotising pancreatitis and reports with a fatal outcome. If you develop persistent, severe abdominal pain, contact your GP promptly or call NHS 111 for urgent advice.

• Gallbladder-related conditions, including gallstones, have been reported.

• Rodent studies identified C-cell thyroid changes with this drug class; the relevance to humans is uncertain, and UK SmPCs advise counselling on symptoms such as a neck lump or persistent hoarseness rather than routine calcitonin testing.

• People with pre-existing pre-proliferative or proliferative diabetic eye disease should be aware that rapid improvement in blood glucose control may be associated with transient worsening of diabetic retinopathy.

• When these medicines are used alongside insulin or sulfonylureas in people with diabetes, the risk of hypoglycaemia is increased; your prescriber will advise on monitoring and any dose adjustments needed.

Orlistat: Oily stools, faecal urgency, and fat-soluble vitamin deficiency with long-term use are the main concerns. Orlistat can reduce absorption of some medicines, including warfarin and levothyroxine; inform your prescriber of all medicines you take.

Mysimba (naltrexone/bupropion): Nausea, headache, and elevated blood pressure have been reported; it is contraindicated in uncontrolled hypertension and seizure disorders, and must not be used with monoamine oxidase inhibitors or opioids.^[23][24]

Pregnancy, breastfeeding, and contraception: These medicines are generally not recommended during pregnancy or breastfeeding. Effective contraception is advised during treatment, and you should inform your prescriber immediately if you become pregnant or are planning a pregnancy, so that treatment can be reviewed before conception.

Suspected side effects from any of these medicines can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk. If you experience signs of a severe allergic reaction, call 999 immediately. For other concerning symptoms, contact your GP or call NHS 111.

How do you get a prescription for weight loss medication on the NHS?

NHS access is determined by NICE guidance and local commissioning decisions; the usual pathway is a GP referral to a specialist weight management service, though availability varies across England, Scotland, Wales, and Northern Ireland.

NHS access to prescription weight loss medicines is determined by NICE guidance and local commissioning decisions, which means availability can vary across the UK. In England, Integrated Care Boards (ICBs) make local commissioning decisions following NICE technology appraisals. In Scotland, the Scottish Medicines Consortium (SMC) advises NHS Scotland territorial boards. In Wales, the All Wales Therapeutics and Toxicology Centre (AWTTC) advises health boards. In Northern Ireland, the Department of Health and Health and Social Care (HSC) trusts apply their own processes. Meeting NICE or equivalent criteria does not automatically guarantee that a specific medicine will be funded locally.

To access treatment through the NHS, the usual pathway is:

1. Speak to your GP: A GP can assess your eligibility, review your medical history, and refer you to a specialist weight management service if appropriate.
2. Specialist weight management services: NICE guidance on medicines such as tirzepatide and semaglutide typically recommends initiation within a specialist or tier 3 weight management service, though this is evolving.
3. Eligibility criteria: These generally include a BMI of 30 kg/m² or above (or 27.5 kg/m² or above in certain ethnic groups) alongside at least one weight-related comorbidity, though exact thresholds differ by medicine and local policy.

For those who do not meet NHS criteria, or where NHS waiting times are lengthy, private prescribing through a regulated online pharmacy or clinic is an option. Any private prescriber must be registered with the GMC (gmc-uk.org) and any pharmacy dispensing the medicine in Great Britain must be registered with the GPhC. Prescriptions issued privately carry the same clinical standards and safety obligations as NHS prescriptions. Private costs vary and are separate from NHS prescription charges; never confuse a private consultation or medicine cost with the standard NHS prescription charge.

Are there lifestyle changes that make prescription treatment more effective?

Prescription weight loss medicines are significantly more effective when combined with a calorie deficit, at least 150 minutes of moderate physical activity per week, and behavioural support, as no medicine works optimally in isolation.

Prescription weight loss medicines are significantly more effective when combined with sustained dietary changes, increased physical activity, and behavioural support, and this combination is reflected in NICE guidance across all approved medicines. No medicine works optimally in isolation.

Dietary changes that support treatment:

• Reducing overall calorie intake, typically by 500 to 600 kcal per day below estimated requirements, is a widely recommended starting point in line with NICE obesity guidance.^[28]

• Prioritising protein and fibre-rich foods can help manage appetite, which is particularly relevant when GLP-1 medicines are already reducing hunger signals.

• Limiting ultra-processed foods and alcohol supports both weight loss and tolerability, as fatty or rich meals can worsen gastrointestinal side effects with orlistat and GLP-1 medicines.

Physical activity:

• UK Chief Medical Officers' guidelines recommend at least 150 minutes of moderate-intensity activity per week for adults.^[26][27] Resistance exercise is particularly valuable during weight loss to help preserve lean muscle mass.

• Even modest increases in daily movement, such as walking, can meaningfully support treatment outcomes.

Behavioural support:

• Cognitive behavioural approaches, group programmes, and regular check-ins with a healthcare professional improve long-term adherence to both lifestyle changes and medication.

• Keeping a food and activity diary can help identify patterns that undermine progress.

It is worth noting that weight loss medicines are intended as an adjunct to, not a replacement for, lifestyle intervention. When medicines are stopped, weight regain is common unless lifestyle habits have been durably changed. Discussing a long-term maintenance plan with your prescriber from the outset is an important part of treatment planning.

Scientific References

1. Orlistat safety update.
2. Single-dose 7.2 mg semaglutide (Wegovy) pen approved to treat adult patients with obesity.
3. Semaglutide 7.2 mg dose for managing obesity ID6699.
4. First GLP-1 tablet for weight loss approved in the UK.
5. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss.
6. Tirzepatide: a medicine to manage type 2 diabetes and obesity.
7. Tirzepatide | Drugs | BNF – NICE.
8. UK first in Europe to authorise orforglipron for weight management and type 2 diabetes.
9. Overweight and obesity management (NG246).
10. Women on 'skinny jabs' must use effective contraception, MHRA urges in latest guidance.
11. One-year treatment of obesity: a randomized, double-blind, placebo-controlled study of orlistat.
12. A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management (SCALE Obesity and Prediabetes).
13. Efficacy of Liraglutide for Weight Loss Among Patients With Type 2 Diabetes (SCALE Diabetes).
14. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1).
15. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity (STEP 4).
16. Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP).
17. Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP) – PubMed record.
18. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1).
19. GLP-1 receptor agonists and dual GLP-1/GIP receptor agonists: strengthened warnings on acute pancreatitis, including necrotising and fatal cases.
20. Suitability of the ICH S1B(R1) weight-of-evidence framework to evaluate GLP-1RA carcinogenicity risk. Regulatory Toxicology and Pharmacology.
21. Suppressed thyroid stimulating hormone levels after initiation of a subcutaneous GLP-1 receptor agonist in a post-thyroidectomy patient. Journal of the American Pharmacists Association.
22. On-target effects of GLP-1 receptor agonists on thyroid C-cells in rats and mice. Toxicologic Pathology.
23. Naltrexone with bupropion | Drugs | BNF – NICE.
24. Naltrexone/bupropion (Mysimba): risk of adverse reactions that could affect ability to drive.
25. Package leaflet: Mysimba 8 mg/90 mg prolonged-release tablets.
26. UK Chief Medical Officers' physical activity guidelines.
27. Physical activity guidelines for adults aged 19 to 64.
28. Overweight and obesity management (NG246) – Physical activity and diet chapter.

Frequently Asked Questions