Prescription Weight Loss Pills in the UK: what’s available, and what isn’t

​

If you’ve been searching for “prescription weight loss pills”, “phentermine 37.5 mg” or “Qsymia pills Amazon”, you’ll mostly be seeing US-focused content – which can be very misleading if you live in the UK.

In the UK:

• Some prescription weight loss medication is available in pill form

• Many famous Rx diet pills from the US are not licensed here

• Newer, more effective injectable treatments (like GLP-1s) are often used instead of older stimulants

This guide explains:

• Which prescription weight loss pills are actually licensed in the UK

• Why drugs like phentermine and Qsymia are not routinely used here

• How doctors decide whether to prescribe doctor-prescribed pills for weight loss at all

• Why “no-questions” online pills are a serious red flag

• Where evidence-based alternatives (like GLP-1 injections) fit in

1. UK vs US: totally different landscapes for Rx diet pills

A lot of the hype you see online is US-specific. In the US, commonly discussed prescription diet pills / appetite suppressants include:

• Phentermine (e.g. 37.5 mg tablets/capsules)

• Qsymia (phentermine + topiramate)

• Contrave (bupropion + naltrexone – EU version is Mysimba)

• Liraglutide, semaglutide, etc., on the injectable side

In the UK, it’s very different:

• Phentermine is not widely used or routinely prescribed for weight loss

• Qsymia is not licensed in the UK or EU

• The main licensed oral prescription weight loss medication are:

  • Orlistat (Xenical – prescription; Alli – OTC lower dose)

  • Naltrexone/bupropion combo under the brand Mysimba (EU/UK brand similar to US Contrave)

And for many patients who qualify, injectables (GLP-1 and similar) have now become first-line weight-loss medicines rather than traditional “diet pills”.

2. What prescription weight loss pills are licensed in the UK?

Orlistat (Xenical, Alli)

Orlistat is the best-known prescription weight loss pill in the UK.

• How it works: Blocks up to about one-third of dietary fat from being absorbed in the gut. The unabsorbed fat is excreted in the stool.

• Brands & strengths:

  • Xenical® 120 mg – prescription-only

  • Alli® 60 mg – lower dose, pharmacy/OTC with pharmacist advice

• Who it’s for: Adults with BMI ≥ 30 kg/m², or BMI ≥ 28 kg/m² with risk factors, combined with a low-fat, reduced-calorie diet (criteria differ for Xenical vs Alli packs).

• Main side-effects:

  • Oily or fatty stools

  • Urgent bowel movements

  • Flatulence with discharge

  • Possible fat-soluble vitamin deficiencies if used long-term

Because orlistat doesn’t affect appetite or the brain like stimulants, it’s sometimes preferred for patients where psychiatric or cardiovascular safety is a concern – but the GI side-effects can be significant if dietary fat is not reduced.

You’d typically link to a separate Orlistat/Xenical/Alli deep-dive article from here.

Mysimba (naltrexone/bupropion)

Mysimba is a fixed-dose combination of two drugs:

• Naltrexone – usually used for addiction

• Bupropion – an antidepressant and smoking-cessation medicine

Mechanism: Works on brain reward and appetite centres, helping reduce cravings and hunger.

Licensed indication (EU/UK):

• Adults with BMI ≥ 30 kg/m², or

• BMI ≥ 27 kg/m² with at least one weight-related comorbidity (e.g. type 2 diabetes, high cholesterol, controlled hypertension) – always combined with diet and physical activity.

Key considerations:

• Side-effects: Nausea, headache, insomnia, dry mouth, dizziness; it can raise blood pressure and heart rate in some, so vitals need monitoring.

• Psychiatric considerations: Because bupropion affects neurotransmitters, clinicians are cautious in people with certain mental health conditions or seizure risk.

Mysimba is a good example of prescription appetite suppressant / craving modulator that’s actually used in the UK – but strictly under medical supervision.

3. What about phentermine, phentermine 37.5 mg, and Qsymia?

This is where UK vs US gets really confusing.

Phentermine

In the US, phentermine tablets (e.g. phentermine 37.5 mg / “phentermine 375”) are one of the most common Rx diet pills. They’re stimulant-like appetite suppressants, somewhat similar in action to amphetamines, used short-term in obesity treatment.

In the UK/EU:

• Phentermine has historically existed in some markets, but it is not a mainstream, widely used obesity drug the way it is in the US.

• NICE and UK obesity guidelines do not list phentermine as a routine option, and it’s not something a typical GP or weight-loss clinic will prescribe.

• Safety concerns (cardiovascular, psychiatric, dependence potential) have made stimulant-type prescription appetite suppressants far less acceptable in European practice.

So if you search “phentermine weight loss UK” or “phentermine diet pills online”, you’ll mostly get:

• Non-UK sites

• Questionable online pharmacies

• Forums where users share experiences acquired abroad

For a UK reader, the safest mental model is: phentermine is not a standard, evidence-based obesity treatment here.

Qsymia

Qsymia (phentermine + topiramate) is approved in the US as a chronic weight-management medication.

In the UK and EU:

• Qsymia is not licensed

• Qsymia pills on Amazon or “Qsymia for sale in the UK” are either:

  • Being shipped from abroad

  • Or not genuine Qsymia at all

Any UK-based consumer trying to order Qsymia pills Amazon-style is almost certainly stepping outside UK regulatory protection.

4. How doctors decide on prescription weight loss medication

Regardless of whether we’re talking about pills, injections or other Rx diet meds, UK clinicians follow broad principles.

A doctor considering weight loss pills prescribed by doctors will assess:

1. BMI & weight-related health risks

• Is your BMI high enough to justify prescription treatment?

• Do you have weight-related comorbidities, such as:

  • Type 2 diabetes or pre-diabetes

  • High blood pressure

  • High cholesterol

  • Sleep apnoea

  • Joint problems, PCOS, etc.

Most prescription weight loss pills (and injectables) are intended for overweight/obesity with health risks – not for dropping a dress size from normal BMI.

2. Medical history & other medication

Your doctor will review:

• Cardiovascular history: heart disease, arrhythmias, uncontrolled hypertension

• Gastrointestinal and liver disease: important for drugs like orlistat

• Kidney function

• Seizure history and psychiatric history: crucial for Mysimba and any stimulant-like drugs

• Current meds: interactions with antidepressants, anticoagulants, diabetes meds, etc.

3. Mental health & relationship with food

Responsible prescribers look at:

• Current or past eating disorders (e.g. bulimia, binge-eating disorder)

• Significant depression, anxiety or bipolar disorder

• Risk of misuse of stimulant-type medicines

Some patients may be diverted toward psychological or dietitian support or GLP-1 programmes rather than appetite-suppressant pills.

4. Ability to commit to lifestyle changes

All doctor prescribed pills for weight loss should be used as an adjunct to lifestyle, not in place of it.

A clinician will typically only prescribe if you’re also:

• Ready to make realistic changes in eating patterns

• Able to increase physical activity at least modestly

• Willing to attend follow-up reviews

5. Why “no-questions” online prescription diet pills are dangerous

You’ll see many sites advertising:

• “Prescription weight loss pills online – no doctor visit”

• “Prescription appetite suppressant shipped in 24 hours”

• “Phentermine 37.5 mg without prescription”

For UK patients, these pose several serious risks:

1. They bypass medical assessment

   • No check of BMI, blood pressure, comorbidities, pregnancy status, mental health or drug interactions.

2. You may receive an unlicensed or counterfeit product

   • Pills labelled as “phentermine” or “Qsymia” might contain completely different substances, or dangerous dosages.

3. No monitoring or follow-up

   • No one checks your blood pressure, mood, liver function or side-effects as you take them.

4. Legal and regulatory risk

   • Importing prescription-only medicines for personal use from outside the UK/EU can sit in a grey or illegal area, and you lose the protection you’d have with regulated UK pharmacies.

Any legitimate UK service for weight loss pills from a doctor will:

• Ask for a detailed medical questionnaire, often plus ID checks

• Have your case reviewed by a GMC-registered doctor or other authorised prescriber

• Dispense only licensed UK medicines via a GPhC-registered pharmacy

• Provide clear written information about risks, side-effects and follow-up

If you don’t see those elements, treat it as a red flag.

6. Pills vs injections: where do GLP-1s fit in?

When people think “doctor prescribed pills for weight loss”, they often imagine something like phentermine. But in modern UK practice, there’s a big shift toward GLP-1 based treatments, which are usually injections, not tablets.

Examples include:

• Wegovy (semaglutide) – weekly injection licensed for weight management

• Saxenda (liraglutide) – daily injection for weight management

• Newer GIP/GLP-1 combos like tirzepatide (Mounjaro) primarily for diabetes, with strong weight-loss effects

These aren’t “pills”, but they are often more effective and better-studied for long-term obesity management than traditional Rx diet tablets.

This is why a comprehensive treatment discussion with a weight-management clinician will usually cover:

• Lifestyle approaches (diet, activity, behavioural support)

• Orlistat or Mysimba (the main UK oral options)

• GLP-1 injectables (Wegovy, Saxenda, etc.)

…rather than immediately jumping to phentermine-style drugs you’ve seen on US TikTok.

You’d typically cross-link here to your GLP-1 hub article plus Wegovy and Saxenda deep dives.

7. Key takeaways for UK patients

• Prescription weight loss pills in the UK mainly means:

  • Orlistat (Xenical, Alli) – blocks fat absorption

  • Mysimba (naltrexone/bupropion) – affects appetite/reward in the brain

• Famous US Rx diet pills like phentermine and Qsymia are not mainstream, licensed UK options, and should not be purchased from unregulated sites.

• Any prescription weight loss medication must be tailored to you after:

  • BMI and health risk assessment

  • Full review of your medical & mental health history

  • Check of all current medications and potential interactions

• Online “no-questions” pills or “Qsymia/phentermine on Amazon” are high-risk: you may be buying unlicensed or counterfeit drugs without any safety monitoring.

• Many UK clinicians now see GLP-1 injectables (like Wegovy or Saxenda) as the more effective evidence-based options for appropriate patients, with pills like orlistat/Mysimba as alternatives depending on individual needs.

If you’re considering weight loss pills from a doctor, the safest route is to:

1. Speak to your GP or a regulated digital weight-loss clinic

2. Have an honest discussion about your weight, health, lifestyle and expectations

3. Explore all options – from lifestyle interventions and orlistat/Mysimba to GLP-1 injectables – rather than chasing the first “phentermine 37.5 mg” advert you see online.