Prescription weight loss medications come in two different forms, injections and tablets, and the right treatment for you will depend on your personal preferences and medical history. Whether you choose weight loss injections or tablets, they are most effective when taken alongside lifestyle changes such as eating healthily and exercising.
Who is eligible for weight loss medication?
Weight loss medications can only be prescribed at ZAVA if you have a body mass index (BMI) over 30, or if you have a BMI of 27 to 30, with one or more weight-related health conditions. Some examples of weight-related medical conditions include prediabetes, type 2 diabetes, high blood pressure, and cardiovascular disease. Weight loss medications can also be considered if your ethnic background puts you at higher risk of obesity related health issues and you have a BMI of 27.5.
Weight loss injections like Mounjaro and Wegovy help you lose weight by reducing your appetite and making you feel fuller after a meal. This means you’ll be more satisfied after a meal with fewer calories. Weight loss injections are the most effective weight loss treatment for most people, and can help you lose on average between 8% and 22.5% of your starting body weight.
Weight loss injections come as pens that you inject yourself with at home. You usually inject yourself in the stomach, thigh, or upper arm (with help) – wherever is most comfortable for you.
Mounjaro is an injectable weight loss treatment. It contains the active ingredient tirzepatide, which mimics 2 naturally occurring hormones in your body called glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). They both help your body control your appetite and how full you feel. Mounjaro helps you lose weight by reducing hunger and prolonging how satisfied you feel after a meal.
Wegovy is a weight loss injection that contains the active ingredient semaglutide, which acts like GLP-1. Usually, after you have eaten a meal, your intestines release GLP-1 to tell your brain that you have eaten. Wegovy works the same way and sends signals to your brain that you are full, so you can eat less and reduce your weight. Like Mounjaro, it also increases feelings of fullness after a meal.
Liraglutide (generic Saxenda) is another injection available to help you lose weight. It contains a different ingredient also mimicking GLP-1, called liraglutide. Like Wegovy and Mounjaro, liraglutide tells your brain you’re full, making it easier to eat less and lose weight with diet and exercise. It is injected once a day. Saxenda contains the active ingredient liraglutide but is currently long-term out of stock.
For patients who do not want to inject themselves or can't take weight loss injections for medical reasons, weight loss tablets might be a suitable alternative.
Weight loss tablets
Weight loss tablets help you lose weight in one of two ways – by reducing how much fat your body absorbs from food (orlistat and Xenical) or suppressing your appetite (Wegovy pills and Mysimba). Weight loss tablets are less effective than weight loss injections according to studies, but may be a good option if you are uncomfortable with injections.
Wegovy pills have the same active ingredient as Wegovy injections – semaglutide. Like with the injections, Wegovy pills affect your brain chemistry, making you feel fuller after eating. This helps you eat less and lose weight alongside a diet and exercise plan.
Orlistat and Xenical contain the active ingredient orlistat. When taken with a meal that contains fat, it attaches to the enzymes in your digestive system, called lipase. Orlistat blocks lipase from breaking down fat in your food and absorbing it. This means some of the fat from your meal will turn into waste and be eliminated from your body as stool. alli is an over-the-counter weight loss tablet that also contains orlistat, but at a lower dose of 60mg. Orlos capsules are another branded, over-the-counter treatment containing orlistat at the same 60mg dose as alli.
Mysimba works differently than orlistat. Instead of having an effect on the digestive system, it works on the areas of your brain that control energy levels and food intake. This can reduce your appetite so that you feel fuller when you eat less. The combination of the 2 active ingredients in Mysimba can also control the pleasure you get from eating, reducing food cravings.
When you take any weight loss treatment, our doctors will review your weight regularly and make sure it is working as it should. Any weight loss medication must be taken alongside a healthy diet plan and regular exercise. Here at ZAVA, we send out a doctor and in-house nutritionist-approved support pack with your first weight loss medication order. You can also access doctor advice for free through your patient account.
Which weight loss treatment is right for me?
When choosing which weight loss treatment is right for you, it's important to consider:
whether you'd prefer taking tablets or using an injectable pen
whether you will remember to take a daily injection like liraglutide, or you'd find it easier taking a once-weekly injection like Wegovy or Mounjaro
your current BMI, as this will determine which medications you are suitable for
how you want your weight loss medication to work – reducing appetite (Mounjaro, Wegovy, liraglutide, and Mysimba) vs reducing how much fat you absorb (orlistat products)
your budget
how much weight you want to lose, as some medications have been proven to show a larger percentage of weight loss than others
"It's important to read about each weight loss medication and how they work to see which you’d prefer. Your doctor will also check your medical history and make sure your chosen treatment is suitable, or offer an alternative if possible. Weight loss injections often cause more weight loss in clinical trials, however, all weight loss medications can be effective when taken alongside a reduced-calorie, balanced diet, and enough exercise.” – Dr Clair Grainger
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How do weight loss treatments work?
Each weight loss medication works in a slightly different way, as they contain different active ingredients. Wegovy, Mounjaro, Saxenda, generic liraglutide and Mysimba all work on the brain and other organs, to reduce appetite levels and cravings, making it easier to eat less and lose weight.
Orlistat, alli, Orlos, and Xenical work by changing how your body digests fat. alli is actually an over-the-counter weight loss pill, but a doctor or pharmacist still needs to check your BMI and medical history to make sure it’s suitable.
How do weight loss injections work?
Weight loss injections and GLP-1 tablets work similarly because they all belong to a class of medications called glucagon-like peptide-1 (GLP-1) agonists. This means they mimic GLP-1, a naturally occurring hormone that:
reduces appetite, helping you to eat less
delays the emptying of your stomach, helping you to stay fuller between meals
regulates your blood sugar levels which can help manage diabetes (if you have it) and reduces food cravings
Mounjaro also mimics a second hormone called glucose-dependent insulinotropic peptide (GIP). This is thought to enhance the effects of GLP-1 while improving how your body breaks down sugar and fat.
How do weight loss tablets work?
GLP-1 pills, such as Wegovy tablets, work in a similar way to weight loss injections. They mimic the GLP-1 hormone that controls appetite, helping you stay fuller for longer after eating. The main difference is how the medication enters your body – Wegovy pills enter through the digestive system and GLP-1 injections are inserted under the skin.
Orlistat (Xenical, alli, Orlos) is a type of medication called a lipase inhibitor. This means when you eat a meal containing fat it blocks the absorption of about a third of it, and instead, this is excreted from your body in your stools. It’s recommended to take orlistat 3 times a day and consume about 30% of your daily calories in the form of healthy fats, split evenly across each of these 3 meals.
Mysimba contains 2 active ingredients called naltrexone and bupropion. They are usually used to treat different conditions but when taken together work on the parts of your brain that control appetite, reducing hunger and the desire to snack.
Side effects of weight loss treatment
Weight loss treatment can have side effects, just like any other medication. Not everyone will get them, and if they do appear, they usually only last for a few weeks, though they could come back after increasing your dose. If you get side effects whilst taking weight loss treatment and they do not go away or bother you a lot, you can speak to our doctors.
Some treatments are increased gradually over time to reduce the chances of side effects. You can find the full list of known side effects in the patient information leaflet that comes with your treatment pack.
Weight loss injection side effects
Common Wegovy side effects
The most common side effects of Wegovy are:
headaches
feeling sick
being sick
diarrhoea
constipation
stomach pain
feeling weak or tired
The side effects usually go away over time.
Common Mounjaro side effects
Very common side effects of Mounjaro are:
diarrhoea
constipation
feeling sick (nausea)
being sick (vomiting)
when used for type 2 diabetes treatment in combination with certain diabetes medications: low blood sugar
stomach pain
Side effects that affect the digestive system are usually not severe. They mostly show up after starting the treatment or after increasing the dosage – once the body gets used to the medication, these side effects usually disappear.
Common liraglutide side effects
Very common side effects of liraglutide include:
nausea
vomiting
diarrhoea
constipation
headaches
These side effects usually go away after a few days or weeks.
Weight loss tablets side effects
Common Mysimba side effects
Common Mysimba side effects include:
hot flushes
anxiety
trouble sleeping
headaches
dizziness
restlessness
heart palpitations
These usually go away once your body gets used to the medication. You cannot take Mysimba if you have certain medical conditions or take certain medications, but our doctors will check your suitability before prescribing.
Common orlistat, alli, and Xenical side effects
The most common side effects of orlistat, alli, and Xenical are:
needing to poo urgently and more frequently
oily or fatty poo
oily discharge from your rectum (anus)
flatulence (farting)
Sticking to a low-fat diet will decrease the risk of these side effects.
Common Wegovy tablet side effects
Wegovy pills share similar same side effects as the injection. The most common ones include:
dizziness
burping
gas (flatulence)
bloating
inflammation of the stomach lining (gastritis)
reflux or heartburn (gastro-oesophageal reflux disease (GERD))
taste changes
gallstones
hair loss
taste changes
abnormal skin sensations, like burning, stinging, or pins and needles (dysaesthesia)
low blood sugar (hypoglycaemia) in people with type 2 diabetes
Who shouldn't use weight loss medication?
People can’t take GLP-1 agonists like semaglutide and other weight loss injections if they have existing health conditions that make them unsafe.
Weight loss injections may not be safe for:
people taking certain medications, such as certain diabetes medications (including insulin)
pregnant or breastfeeding women
those with current pancreatic disorders, such as pancreatitis
people with severe liver or kidney disease
those with a history of a significant eating disorder
How else can I lose weight?
Alongside medication, you can support your weight loss journey with healthy eating and regular exercise. Surgery is sometimes considered when other weight loss methods haven’t worked and should generally be a last resort.
Diet
To lose weight at a safe pace of 0.5 to 1kg a week, you should reduce your calorie intake by 600 calories a day for most people. Your doctor will help you with a diet plan if you need it. This is not about following a ‘fad’ diet, but about making healthier long lasting choices that will improve your eating habits for the rest of your life.
Generally, for women, weight loss can be achieved by consuming no more than 1,400 calories a day. Men should be eating no more than 1,900 calories daily. To lose weight, you should swap high-energy and unhealthy foods for healthier choices. This means lowering your intake of processed food, fast food, and sugary drinks like sodas and alcohol.
Exercise
Although a healthy and balanced diet can help you to lose weight, you also need to burn energy through regular exercise. The UK government recommends that adults do at least 150 minutes of moderate intensity exercise weekly. This can be split into 30 minute sessions 5 times a week. Some exercise is better than none, so if you struggle to exercise, you can increase this slowly, starting with 10 minutes a day.
Exercise has many health benefits and can reduce the risk of other illnesses that can affect your weight. According to the NHS, regular exercise can reduce the risk of getting type 2 diabetes by up to 30%.
Surgery
Weight loss surgery can sometimes be used as a treatment for obesity. It is only available through the NHS if you are severely obese and:
are fit enough to have surgery
have a BMI over 40, or between 35 and 40 and certain health conditions that weight loss could improve, such as type 2 diabetes
are committed to the long term follow up of your surgery
you have tried all other weight loss strategies but they have not achieved or maintained weight loss
are receiving intensive management of your weight, usually through your GP
In rare cases, surgery may be recommended straight away if you have a BMI over 50.
FAQs
Are weight loss injections safe?
Weight loss injections are safe when prescribed by a doctor and used correctly. A doctor needs to review your medical history and make sure weight loss injections are safe for you. They’ll also discuss any side effects, risks, and benefits of using weight loss injections. This can help you make an informed decision about using treatment.
Weight loss injections, like all prescription medications, have the chance to cause some serious side effects. Most people will not experience these but they can happen. You should read the patient information leaflet that comes with your medication and let your doctor know if you’re getting any side effects from your treatment. Although it’s common to get mild side effects, these should go away as you continue treatment.
➤ For more information on weight loss injection side effects, who can safely be prescribed with weight loss medication, and what to do if you get side effects, we recommend reading our doctor-reviewed weight loss injection safety guide.
What’s the best weight loss pill?
The best weight loss pill for you depends on many factors, including your preferences, suitability, and BMI. The most popular weight loss pills in the UK are Wegovy pills, orlistat (also called Xenical, Orlos, and alli), and Mysimba.
Weight loss pills containing orlistat can be a great choice if you’re happy to follow a reduced-fat diet and want a pill that can help you lose weight by reducing how much fat you absorb from your meals. Mysimba is another great choice if you’d prefer a weight loss pill that works on your appetite to help you reduce how many calories you consume. Similarly, Wegovy pills can also reduce appetite and slow down digestion, like weight loss injections do.
Which weight loss injection is the best?
Mounjaro has shown the highest rate of weight loss in clinical studies at 22.5%. However, results vary from person to person and other factors like side effects may also affect which injection works best for you.
All weight loss injections work in a very similar way, so which one is best for you usually comes down to preference and suitability. Liraglutide, Wegovy, and Mounjaro can all reduce your appetite and leave you feeling fuller for longer. Mounjaro is the only weight loss injection that mimics 2 hormones which is thought to enhance appetite suppression and digestion further.
Wegovy has an average weight loss of 21%, while liraglutide has an average weight loss of about 8%. These figures are based on people who have gradually increased their dose to reach the maximum recommended doses of each medication.
Who is eligible for weight loss medication?
At ZAVA, you may be eligible for weight loss medication if you have a BMI over 30 and have no condition or current medications that interact with your chosen treatment. You may also be eligible if you have a BMI between 27 and 30 and also have a weight-related health condition, or a BMI >27.5 if your ethnic background is associated with an increased risk of obesity related complications.
Eligibility for weight loss medication is different on the NHS and usually, you need at least a BMI over 30.
What should I eat on weight loss medicaiton?
Regardless of the weight loss medication you are taking, you should be eating a healthy, balanced diet and reducing your daily calories for safe and sustainable weight loss.
This usually involves eating 600 calories less than your recommended daily intake and should include:
plenty of fruit and veg
some complex carbohydrates
some healthy, lean sources of protein from meat, fish, or plant-based alternatives
Dr Clair Grainger did her undergraduate studies at The University of Edinburgh between 2004 to 2009. She completed her training as a GP at North Middlesex Hospital in 2017. Her experience includes hospitals throughout Edinburgh and London. Clair has been at ZAVA since 2018, and also works as an NHS GP. Her professional interests include respiratory, sexual, and reproductive health.
Last reviewed: 16 Jun 2026
Real results from ZAVA weight loss patients
Fiona, Newcastle
“It feels good to look in the mirror...”
“... and I feel much happier than before. Everything – so life in general – feels better.”
Neil, H., Scotland
“I use the phrase genuinely life changing...”
“... I feel normal again and not embarrassed about my size.”
A. P., London
“At my heaviest, I simply didn't recognise myself...”
“... Today, I feel like my old (youthful) self.”
Anna, Scotland
“I have regained so much more stamina and energy...”
“... since I started taking the medication - the entire experience is definitely worth it!”
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