Weight-loss medicines: how do they fit into obesity treatment?

Which medicines are used to treat obesity?

Several medicines can support weight management in eligible patients.

Examples include:

• Semaglutide, marketed as Wegovy for weight management;
• Tirzepatide, marketed as Mounjaro, which is licensed for weight management in eligible people as well as for type 2 diabetes;
• Other options, including liraglutide and orlistat, depending on the person’s circumstances and the relevant prescribing criteria.

The choice of medicine depends on overall health, body mass index (BMI), weight-related conditions, other medicines and potential risks.

Brand names and licensed uses matter. For example, Ozempic also contains semaglutide but is licensed for type 2 diabetes, rather than weight management.

How do weight-loss medicines work?

Some newer treatments act on receptors for gut hormones involved in regulating appetite.

Semaglutide is a GLP-1 receptor agonist. Tirzepatide acts on both GIP and GLP-1 receptors.

These medicines can reduce hunger, increase feelings of fullness and help people eat less. Other weight-management medicines work differently. For example, orlistat reduces the amount of dietary fat absorbed in the gut.

Medication is used alongside an appropriate eating plan and physical activity adapted to the person’s health and abilities.

Who are these treatments for?

Weight-management medicines are not suitable for everyone who wants to lose a few kilograms.

For adults, the licensed weight-management indications for Wegovy and Mounjaro include:

• Obesity, with a BMI of 30 kg/m² or higher;
• Overweight, with a BMI of 27 kg/m² or higher, together with at least one weight-related health condition.

However, being eligible under the medicine’s licence does not automatically mean that it is available on the NHS.

NHS prescribing criteria can be more restrictive. NICE recommendations for tirzepatide include a BMI of at least 35 kg/m² and at least one weight-related condition, with lower BMI thresholds for certain ethnic backgrounds. Access in England is being introduced in phases, so not everyone meeting these recommendations can immediately receive treatment.

Wegovy has separate NHS criteria and is generally provided through specialist weight-management services. Arrangements differ across the UK and between local services.

Your GP or weight-management team can explain which options are available and appropriate for you.

What are the possible side effects?

Like all medicines, obesity treatments can cause side effects.

With semaglutide and tirzepatide, common side effects mainly affect digestion:

• Nausea;
• Diarrhoea;
• Vomiting;
• Constipation;
• Abdominal discomfort.

Less common but serious problems can include pancreatitis, gallbladder problems and dehydration-related kidney problems. Low blood sugar is more likely when these treatments are combined with certain diabetes medicines.

Seek urgent medical attention for severe, persistent abdominal pain, especially if it spreads to the back or occurs with vomiting.

These medicines should not be used during pregnancy. Discuss pregnancy plans and contraception with your prescriber before starting treatment.

If you take Mounjaro and use an oral contraceptive pill, you may need an additional barrier method or a non-oral contraceptive for four weeks after starting treatment and for four weeks after each dose increase. Your prescriber or pharmacist can advise you.

Can you take weight-loss medicine without medical supervision?

Wegovy and Mounjaro require a prescription and appropriate medical follow-up, whether obtained through the NHS or privately.

They should not be used solely for cosmetic weight loss without a medical indication. A clinician needs to assess whether the expected benefits outweigh the risks.

Some lower-dose orlistat products may be available through a pharmacy without a prescription, but a pharmacist must assess whether they are suitable.

Buying products from unverified websites or social media sellers can expose people to falsified or inappropriate medicines. Use a registered pharmacy and avoid products sold without the assessment or prescription they require.

Do medicines replace nutrition and physical activity?

No. Medication is one part of comprehensive obesity care.

Nutritional support and physical activity remain important during treatment. These should be realistic, sustainable and adapted to the person’s medical needs.

The aim goes beyond lowering the number on the scales. Treatment should also support health, daily functioning and quality of life, while addressing weight-related complications.

Needing medication is not a personal failure. Obesity is a chronic condition, and different people need different forms of support.

What happens after treatment stops?

Stopping obesity medication should be discussed with the prescribing clinician.

Weight regain is common after stopping semaglutide or similar treatments. Research has shown that a substantial proportion of lost weight can return after treatment withdrawal, although the amount varies between individuals.

This reflects the ongoing nature of obesity and the return of appetite-related effects when treatment ends. It does not mean that someone has failed.

Some people may benefit from long-term treatment, although NHS treatment duration and continuation rules depend on the medicine and care pathway.

Decisions about continuing, changing or stopping treatment should consider its benefits, side effects and the person’s preferences. A follow-up plan remains important after treatment stops.

Weight-loss medicines: what should you remember?

Obesity medicines can be useful treatments for eligible patients. Semaglutide and tirzepatide are among the options used to support weight management.

They require a personalised care plan, including nutritional support, physical activity and medical monitoring.

If you are considering treatment, speak with your GP or weight-management team about your health needs, treatment goals, possible side effects and available services.

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