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Weight loss medications: are they right for you?

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 5 minutes read

Losing weight can be extremely challenging for some people. Even with a change in diet and increased exercise, they may still struggle to lose it. In scenarios like this, weight loss medication could be the answer. Different prescription weight loss drugs are available, but you may be wondering how effective they actually are and which one is right for you.

In this guide, we explore your options with weight loss mediation.

What are weight loss medications?

There are different weight loss medications available and they all aim to help people lose weight. If the calories you eat exceed the calories you burn off, this will result in gaining weight. People who regularly eat more calories than they burn will likely become overweight or even obese. Weight loss medication is usually prescribed by your doctor, but some can be purchased from your pharmacy.

How do weight loss medications work?

Weight loss medications work by doing one or more of the following:

  • Reducing appetite; if you feel fuller you won't want to eat as many calories

  • Reducing the rate at which nutrients such as fat are absorbed, lowering your calorie intake

  • Increasing fat burning so you don’t store as many calories in your body

Combined with a healthy diet and regular exercise, this type of medication can help you lose weight.

How well does weight loss medication work?

Using weight loss drugs can be an effective way to lose weight that you’ve been unable to shift through diet and exercise.
Combining weight loss medication with positive lifestyle changes can lead to good results and can help you lose between 5% to 15% of your total body weight, which can have significant health benefits. Lowering blood pressure, blood sugar levels, and reducing the amount of fat can considerably improve your overall health.

Prescription weight loss drugs

Prescription weight loss medication can be prescribed by your doctor if they feel you will be unable to lose this excess weight through diet and exercise alone. Some prescription weight loss medication can be used for more than 12 weeks, making it a long-term treatment option.

What can a doctor prescribe for weight loss?

Currently the only approved and licensed weight loss medications available in the US are:

  • Orlistat: Can be bought under the brand name Xenical. Suitable for adults with a BMI over 27 kg/m2. Alli is a reduced-strength form that doesn’t require a prescription.

  • Saxenda: Brand name for liraglutide, a type of glucagon-like peptide-1 (GLP-1) analogue injected daily. It’s suitable for adults with a BMI over 27 kg/m2 who also have a weight related issue or those with a BMI over 30 kg/m2 classed as obese. Children between 12-17 years with a body weight over 60 kg and classed as obese may be prescribed it to lose weight.

  • Wegovy: Wegovy is a brand name for semaglutide, a GLP-1 analogue. Prescribed for people who have a BMI over 30 kg/m2 (obese) or a BMI over 27 kg/m2 and at least one weight-related health condition like type 2 diabetes. Those classed as having prediabetes may also be eligible.

  • Zepbound: Brand name for a new class of drug called a glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptor agonist. It aims to reduce blood sugar levels and slow absorption of food. Zepbound contains the same active ingredient as Mounjaro, a drug only indicated for type 2 diabetes.

  • Contrave: Brand name for naltrexone/bupropion. Labeling for this product indicates that if you do not lose at least 5% of your body weight within 12 weeks, it is unlikely to work for you.

  • Qysmia: Brand name for phentermine/topiramate. This drug should only be used short-term (a few weeks) and works by reducing your appetite.

Should anyone avoid taking weight loss medications?

Weight loss medication should be avoided by people in certain cases.

It’s not suitable if you:

  • Are breast feeding

  • Are pregnant or trying to become pregnant

  • Have problems absorbing food

  • Have the medical condition cholestasis

  • Take cyclosporin

  • Take warfarin or other types of blood-thinning medication

Are there any side effects with weight loss medication?

Like with any medication, there is the possibility that some people may experience side effects. With weight loss medication common side effects include:

  • Flatulence

  • Stomach upset

  • Constipation

  • Diarrhea

  • Fatty or oily stools

  • Sudden bowel motions

  • Stomach pain

Eating foods that are lower in fat can help to reduce the chance of these side effects. You should speak with your doctor or pharmacist if you are worried about any side effects.

How long does weight loss medication take to work?

The speed at which it takes weight loss medication to work depends on different factors. For starters, the specific weight loss drug you are using will work differently and this will affect how quickly you see results.

Some people may see a slight weight loss within the first two weeks of treatment. Results are not immediate and may take several weeks.

Weight loss with orlistat typically happens in the first few months of use. If you’ve regularly exercised and stuck to a set diet and have not lost 5% of your initial body weight, continued use may not be worthwhile.

How long you should take a weight loss drug depends on what your doctor recommends and how quickly it’s working. If you’ve lost weight and it’s improved your health without any notable side effects, they may suggest you use it as a long-term solution to manage weight.


Using weight loss medication can be a viable way to lose weight if you’ve been unable to lower it through conventional methods like changing to a healthy low calorie diet and regularly exercising.

You should only take weight loss drugs that have been prescribed by your doctor or recommended by a healthcare professional. You should carefully follow instructions and only take the advised dose. There may be side effects to consider as well, so you should ask your doctor if you have any concerns about this.

Contact our friendly team today if you have any questions about weight loss medication.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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