Weight Loss Medicine Names: Drug Classes and Active Ingredients

• A complete list of the weight loss medicines licensed in the UK, named by active ingredient and drug class.
• Explains why the active ingredient is the name that matters, and how the same one appears under different names.
• Teaches you to read any medicine name you come across and work out what class it belongs to.
• Online consultation with UK registered prescribers, from a GPhC registered pharmacy, if you want your options reviewed clinically.

There are five active ingredients licensed for weight management in the UK, spread across four drug classes. That is the whole list.

If it feels shorter than expected, it is because most of the names circulating online are brand names, names for the same molecule, names licensed for a different condition, or names not licensed here at all. Knowing which is which is the difference between an informed conversation with a prescriber and buying something unsafe.

This page gives you the names that appear on a prescription, explains what each class does, and teaches you to read any name you come across.

Key things to know

• Five active ingredients are licensed for weight management in the UK: orlistat, liraglutide, semaglutide, tirzepatide, and the naltrexone with bupropion combination.
• The active ingredient is the real name. Brand names are marketing, and the same ingredient can appear under more than one.
• The same active ingredient can be licensed for different conditions at different strengths under different names. Assuming they are interchangeable is a genuine risk.
• Medicine names follow patterns. A name ending in "glutide" tells you it is a GLP-1 receptor agonist before you look anything up.
• Injection or tablet tells you about the format, not the strength. Semaglutide is now licensed in the UK in both forms.
• Several names people encounter online are withdrawn, licensed only in other countries, or were never medicines at all.
• Prescription only medicines cannot legally be advertised to the public in the UK, which is why a regulated pharmacy will not list brands at you.

What are the names of the weight loss medicines licensed in the UK?

Five active ingredients hold MHRA licences for weight management in men aged 18 and over. Here they are by name, class and format. In the wider US market, the FDA approved six drugs for chronic weight management, but this page focuses on UK licences.

A small number of specialist medicines exist for rare genetic causes of obesity. Some are used to treat obesity linked to rare genetic disorders and are prescribed within specialist services only after genetic testing, so they are not part of general weight management.

Every one of these is a prescription only medicine, with the single exception of the lower strength orlistat, which is a pharmacy medicine sold after an assessment by a pharmacist.

Why the active ingredient is the name that matters

The active ingredient is the medicine. The brand name is a label a manufacturer puts on it, and the same ingredient can carry several.

This is not pedantry. It has direct safety consequences, and it is the single most useful thing to understand before you research any of this.

The same active ingredient can appear under different names

One molecule can be licensed for more than one condition, at different strengths, under different names. Semaglutide is the clearest example: it is licensed for type 2 diabetes and separately for weight loss, and those are not the same product even though the active ingredient is identical.

Two mistakes follow from not knowing this, and both are common.

The first is assuming two names are two different medicines, then taking both. If both contain the same active ingredient, that is a double dose. The second is assuming that because the ingredient is the same, a product licensed for one condition can be substituted for another. Licensed indications, strengths and monitoring differ, and a prescriber choosing between them is making a clinical decision rather than a naming one.

If you are ever unsure whether two products contain the same active ingredient, ask a pharmacist. It is a thirty second question with a definitive answer.

Why a UK pharmacy will not give you a brand list

Prescription only medicines cannot legally be advertised to the public in the UK. A regulated pharmacy listing brand names of weight loss injections alongside prices would be advertising a prescription only medicine to you.

This is worth knowing for two reasons. It explains why you will find active ingredient and drug class information on legitimate UK sites but not a shop window of brands. And it gives you a test you can apply anywhere: if a site is promoting named prescription weight loss brands at you as a consumer, with prices and offers attached, either the product is not what it claims to be or the advertising is not compliant.

Neither is a good sign about who you are buying from.

How to read a medicine name

Generic medicine names are built from standardised endings, so the name itself usually tells you the drug class. Once you know a handful of these, you can place almost any name you encounter.

Two things fall out of this immediately. Tirzepatide ends in "tide" but not "glutide", which correctly signals that it is a peptide but not a plain GLP-1 agonist, since it acts on two receptors. And the diabetes endings are worth recognising, because medicines from those classes are sometimes discussed as weight loss options when they are not licensed for it here.

Newer oral medicines in development use different endings again, which is a reminder that this is a shortcut rather than a rule.

The drug classes, and what each one does

Four classes cover everything licensed here. They work in genuinely different ways, which is why side effects and suitability differ so much between them.

GLP-1 receptor agonists

GLP-1 receptor agonists mimic glucagon-like peptide-1, a hormone the body releases after eating, and they also help regulate blood sugar levels by stimulating insulin release, which is why they are also used in diabetes care. They act on the parts of the brain that regulate appetite, so you feel fuller for longer and reduce food intake, and they slow the rate at which the stomach empties.

Liraglutide and semaglutide are the two licensed here for weight management. Liraglutide is a daily injection. Semaglutide is a weekly injection, and since June 2026 also a daily tablet.

The common side effects are digestive: nausea, vomiting, diarrhoea or constipation, usually worst in the early weeks and after each increase in dose, and around 1 in 10 people experience these digestive problems. Less common but more serious problems include gallbladder problems and pancreatitis. Not everyone gets these side effects, but up to 1 in 100 may develop acute pancreatitis and should seek medical advice if symptoms suggest it. Because these medicines slow stomach emptying, they can also affect how other oral medicines are absorbed, which is worth raising if you take regular tablets. Weight can return after stopping treatment as the appetite-suppressing effect wears off.

Dual GIP and GLP-1 receptor agonists

This class acts on two hormone receptors rather than one, adding glucose-dependent insulinotropic polypeptide to the GLP-1 effect, and the active ingredient tirzepatide is the key example of how dual incretin receptor agonists can enhance appetite control and weight loss compared with single-hormone options. Tirzepatide is the only one licensed in the UK, as a weekly injection, authorised by the MHRA for weight management in men aged 18 and over aged 18 and over in November 2023. In clinical trials over 72 weeks, patients lose a substantial percentage of their starting body weight with tirzepatide, and Mounjaro has reported an average reduction of 20.2% in body weight.

Its side effect profile is broadly similar to the GLP-1 class, being mostly digestive and most noticeable early and after dose increases.

Lipase inhibitors

Lipase inhibitors work in the gut rather than the brain. Orlistat blocks some of the enzyme that breaks down dietary fat, so a proportion of the fat you eat passes through undigested.

Because it acts on fat specifically, its side effects are tied directly to how much fat you eat, and include urgent bowel movements, oily stools and wind. Reducing dietary fat reduces the effects, which is why it is prescribed alongside a reduced-calorie, lower fat diet and increased physical activity rather than as a way to eat as before. In trials, people using orlistat lost about 5% of their body weight on average, which helps answer the common question of how much weight these medicines may help with. NICE also recommends using weight-loss medicines alongside a reduced-calorie diet, not as a standalone fix.

One consequence people miss: because it reduces fat absorption, it also reduces absorption of the fat soluble vitamins A, D, E and K. Product information advises taking a multivitamin containing those, separated in time from the medicine.

Combination appetite and reward medicines

The naltrexone and bupropion combination is a fixed dose tablet containing two ingredients that act on appetite and on the brain's reward pathways. Neither ingredient is licensed alone for weight management in the UK.

This one carries more interactions and contraindications than the others, because both ingredients are used in other areas of medicine. Anyone taking opioid medicines, or with a history of seizures, uncontrolled high blood pressure or an eating disorder, needs particularly careful assessment. Naltrexone-bupropion can raise blood pressure and cause headaches. Tell your prescriber about any other medications and prescription medications you take, including monoamine oxidase inhibitors and anything bought over the counter.

Does injection or tablet tell you anything?

Less than it used to. Since the UK licensed an oral semaglutide tablet on 11 June 2026, the same active ingredient exists here in both an injectable and a tablet form. Some people will search for a Wegovy pill, but the key point is checking which semaglutide product and indication are actually licensed in the UK.

The format tells you about administration, not about strength or effectiveness. A tablet is not automatically a weaker option, and an injection is not automatically a stronger one. What matters is which active ingredient it contains and whether you can take it consistently.

There are real practical differences, and they cut both ways. A weekly injection means fewer administrations but requires self injection. A daily tablet avoids needles but must be taken on an empty stomach with a wait before eating or drinking, which suits some routines and not others, partly because the way the body absorbs oral semaglutide is part of why those empty-stomach instructions matter.

Names that are not licensed weight loss medicines in the UK

A great many names circulate that are not on the list above. They fall into three groups, and the distinction matters.

Withdrawn from use

Some appetite suppressants that were once prescribed have been withdrawn from the UK and European market on safety grounds, including sibutramine and rimonabant. Products still sold online under those names are not legitimate, and the safety concerns that caused the withdrawals have not changed.

Licensed elsewhere but not here

Some medicines are approved in other countries and not in the UK. Certain appetite suppressants prescribed in the United States have never held a UK licence for weight management, including phentermine topiramate, which is approved elsewhere but not licensed here for this use. Phentermine may cause insomnia and a rapid heart rate, and studies of phentermine-based prescription drugs have reported roughly 5–10% body-weight loss in some users. Newer oral agents are moving through approval processes in various countries at different speeds, so a name approved abroad may not be available here for some time, or at all.

Being licensed somewhere else is not the same as being legal to supply here, and importing a prescription only medicine for yourself is not a workaround.

Never medicines at all

The third group is the dangerous one. The MHRA has repeatedly warned about illegally supplied slimming products sold online, including those containing 2,4-dinitrophenol, known as DNP, an industrial chemical that has caused deaths in the UK. The MHRA has also seized large quantities of unlicensed and counterfeit weight loss products intended for sale here, some packaged to resemble genuine medicines.

Also in this group are products marketed as compounded or generic versions of the injectable medicines. Those are not licensed in the UK, whatever the listing says.

What the evidence shows

The evidence for these medicines runs over many months, and each has its own trial programme. As obesity is a chronic disease, longer-term management matters, and one prevalence datapoint often cited is that it affects more than 4 in 10 men aged 18 and over in the US. Figures from separate trials should not be lined up and compared, because the studies used different participants, entry criteria and durations.

In the STEP 1 trial, published in the New England Journal, 1,961 men aged 18 and over with obesity, or with overweight plus at least one weight related condition, received once weekly semaglutide or placebo alongside lifestyle support for 68 weeks. Semaglutide was FDA-approved for obesity treatment in 2021. Mean weight change at 68 weeks was 14.9% with semaglutide compared with 2.4% with placebo, with wide variation between individuals. An extension followed a subset for a year after treatment stopped, and they regained around two thirds of the weight lost.

That last finding applies across the class and is the most useful thing to take from any of it. These are treatments for an ongoing condition rather than a course with an end date. Results vary between individuals.

Treatment suitability depends on an individual clinical assessment. Your prescriber will determine the appropriate treatment, and these medicines should only be used under the supervision of an appropriately qualified prescriber. They are not a quick fix and work best as part of longer-term obesity treatment.

How to check any name before you buy

Use these five checks on any name you come across. If you cannot answer all five, do not buy it.

1. Is it an active ingredient or a brand name? Search the ingredient, not the label, and you will find the regulatory information rather than the marketing.
2. Is that ingredient licensed in the UK for weight management? Licensed elsewhere, or licensed here for a different condition, does not count.
3. Is the supplier a registered pharmacy? Registration can be checked through the GPhC register.
4. Is a named prescriber responsible for the decision? There should be someone to contact if something goes wrong.
5. Is the product being advertised to you directly? Prescription only medicines cannot legally be advertised to the public in the UK.

If you already take other medicines, add a sixth: ask a pharmacist whether the ingredient interacts with anything on your list. This class of medicines interacts more than people expect.

Who is not suitable for prescription weight loss medications

Eligibility starts with body mass index thresholds and weight related health conditions: BMI 30 or above is the usual starting point for weight loss medications, with lower thresholds applying to some ethnic groups who face higher weight related health risk at a given BMI.

Beyond that, your prescriber will consider pregnancy or breastfeeding, age, your full medical history and every medicine you already take. These medicines are contraindicated during pregnancy and are not approved for pregnant women. Some medicines may also be used in pediatric patients aged 12 and over when BMI is at or above the 95th percentile, depending on the product and clinical assessment. Some histories rule out a particular class or require specialist input first, including certain thyroid and pancreatic conditions, gallbladder problems, previous bariatric surgery, a history of seizures, current or previous eating disorders, and a personal or family history linked to thyroid cancer warnings. Anyone taking insulin or other medicines that lower blood glucose needs careful review.

Being told a treatment is not appropriate is the assessment working, not failing.

Where a clinical assessment fits

If you are researching names because you are considering a weight loss treatment decision, the useful next step is an assessment rather than a purchase.

As part of a weight loss service, an online consultation is reviewed by a qualified clinician and can help a healthcare professional or other health care professional assess your medical history, current medicines, BMI and any weight related conditions, and advise on whether prescription weight loss medications are appropriate before anything is supplied. Knowing the active ingredient names makes that conversation easier, and primary care services may be part of the wider pathway, although some patients may also need a specialist weight management service depending on complexity and local access.

Medical Disclaimer

This article is for general information and does not replace individual medical advice. It does not diagnose any condition, recommend a specific treatment for you, or compare or rank medicines against one another.

Treatment suitability depends on an individual clinical assessment by an appropriately qualified prescriber, who will consider your medical history and current medicines. Prescription medicines should only be used under the supervision of an appropriately qualified prescriber, and never take one that was not prescribed for you. Never take two products containing the same active ingredient. If you miss a dose, follow the patient information leaflet supplied with the medicine, and do not take a double dose to make up for it. Report suspected side effects through the MHRA Yellow Card scheme.

Results vary between individuals. If you are unwell after taking any product bought outside a registered pharmacy, seek medical advice.