Weight Loss Medications in the UK: Which Are Licensed and What Do They Do?

Weight loss medications are licensed medicines in the UK, regulated by the MHRA (Medicines and Healthcare products Regulatory Agency). They require a prescription. No over-the-counter product in the UK legally makes the same therapeutic claims — because medicines claiming to treat obesity require clinical trial evidence and MHRA approval.

Understanding which medicines are actually licensed in the UK, what they do, and who is eligible prevents confusion between legitimate prescription medicines and unregulated supplements marketed with similar language.

Licensed UK Weight Loss Medications (2024)

Orlistat (Xenical 120mg / Alli 60mg)

Mechanism: Pancreatic and gastric lipase inhibitor. Blocks approximately 30% of dietary fat absorption in the small intestine. The unabsorbed fat passes to the colon.

Evidence: Davidson et al. (1999, JAMA, RCT, n=892, 2 years): orlistat 120mg three times daily plus diet produced approximately 10.3% weight loss vs. 6.1% with placebo — approximately 4.2% additional weight loss vs. placebo.

Side effects: Oily stools, oily spotting, flatulence with discharge, urgent bowel movements — direct consequences of unabsorbed fat. Severity is proportional to fat intake; keeping meals below 15g fat significantly reduces GI effects. Reduced fat-soluble vitamin (A, D, E, K) absorption — a multivitamin 2 hours before or after each dose is recommended.

NICE eligibility: BMI ≥30 (or ≥28 with weight-related comorbidities). Available through NHS GPs and Tier 2 weight management services. Alli 60mg is available OTC at pharmacies for BMI ≥28.

Cost: Alli OTC approximately £30–50/month; Xenical prescription approximately £50–80/month privately.

Liraglutide 3mg (Saxenda)

Mechanism: GLP-1 receptor agonist. Reduces appetite, slows gastric emptying, increases satiety signalling through GLP-1 receptors in the pancreas, gut, and brain.

Evidence: Davies et al. (2015, SCALE trial, Lancet, RCT, n=3,731, 56 weeks): liraglutide 3mg produced mean weight loss of 8.4% body weight vs. 2.8% placebo — approximately 5.6% additional loss.

Administration: Daily subcutaneous injection. Dose escalation from 0.6mg to 3mg over 5 weeks to reduce nausea.

NICE eligibility (TA664, 2020): BMI ≥35 (or ≥32.5 in South Asian, Chinese, Middle Eastern, Black African, or African-Caribbean adults) with a weight-related comorbidity; after completing a Tier 2 programme.

NHS availability: Tier 3 specialist weight management services.

Private cost: Approximately £200–250/month.

Semaglutide 2.4mg weekly (Wegovy)

Mechanism: GLP-1 receptor agonist — same class as Saxenda, but higher receptor binding affinity and weekly dosing.

Evidence: Wilding et al. (2021, STEP 1 trial, NEJM, RCT, n=1,961, 68 weeks): semaglutide 2.4mg weekly produced mean weight loss of 14.9% body weight vs. 2.4% placebo — approximately 12.5% additional loss. 32% of participants lost ≥20% of body weight.

Administration: Weekly subcutaneous injection. Dose escalation over 16 weeks to 2.4mg.

Advantages over Saxenda: Weekly vs. daily injection; approximately double the weight loss.

NICE eligibility (TA875, 2023): BMI ≥35 with at least one weight-related comorbidity, within a specialist weight management service. Implementation is phased due to supply constraints.

NHS availability: Specialist weight management services; access varies by ICB (Integrated Care Board) region. Private prescribers (online clinics) offer it widely.

Private cost: Approximately £200–260/month.

Tirzepatide 15mg weekly (Mounjaro)

Mechanism: Dual GIP and GLP-1 receptor agonist. The additional GIP activation appears to enhance weight loss beyond GLP-1 alone — possibly through increased energy expenditure and fat oxidation.

Evidence: Jastreboff et al. (2022, SURMOUNT-1 trial, NEJM, RCT, n=2,539, 72 weeks): tirzepatide 15mg produced mean weight loss of 20.9% body weight vs. 3.1% placebo. 57% of participants lost ≥20%.

Administration: Weekly subcutaneous injection. Escalation from 2.5mg to 15mg over 16–20 weeks.

NICE eligibility (TA1026, 2024): Similar criteria to semaglutide. Also has a separate diabetes indication at lower doses.

NHS availability: Specialist weight management services; also widely prescribed privately.

Private cost: Approximately £200–280/month.

Comparison Table

What Is Not Licensed in the UK

Phentermine: A controlled stimulant (amphetamine-class) used in the US for short-term weight loss. It is not licensed as a weight loss medicine in the UK and is a Schedule 3 controlled drug. It should not be purchased from online sources.

Topiramate/phentermine combinations (Qsymia): Licensed in the US, not licensed in the UK.

Bupropion/naltrexone (Contrave): Not licensed for weight loss in the UK.

Any online source selling prescription weight loss medicines without a valid UK prescription — or claiming to sell phentermine, Qsymia, or Contrave in the UK — is operating outside UK law.

Accessing Prescription Weight Loss Medicines

NHS pathway:

1. GP assessment (BMI, comorbidities, previous attempts at weight management)
2. Tier 2 referral (for orlistat and structured weight management programme)
3. Tier 3 referral if Tier 2 unsuccessful (specialist service for GLP-1 medications)
4. Tier 4: bariatric surgery (BMI ≥40, or ≥35 with comorbidities)

Private pathway: Multiple UK-registered online clinics (Numan, Voy, Juniper, Manual, Superdrug Online Doctor) provide private prescriptions following a clinical assessment. Requirements:

• BMI typically ≥30
• GP-level clinical assessment
• Ongoing prescription review

MHRA warning (2024): Counterfeit semaglutide and tirzepatide products have been identified in the UK. Do not purchase injectable weight loss medicines from non-prescriber sources. Counterfeits may contain incorrect doses, contaminants, or inactive ingredients.

Disclaimer: This article is for informational and educational purposes only. Weight loss medications require medical assessment and a valid prescription from a registered UK prescriber. Do not use injectable medications without medical supervision.