Weight Loss Injections

Dr Babak Ashrafi Clinical Lead for Service Development

Medically reviewed by

Dr Babak Ashrafi

Last reviewed: 12 Feb 2024

Weight loss injections are injectable medications that can help you lose weight when taken in combination with an exercise and diet plan.

Some weight loss injections are already licensed in the UK, such as Saxenda and Wegovy, and the more recently approved Mounjaro. Below we look at each weight loss injection in more detail and explain how to be prescribed with a weight loss treatment if it’s suitable for you.

What are the different weight loss injections?

There are several different weight loss injections approved in the UK. While the daily injection Saxenda has been on the market since 2015, weekly injections Wegovy and Mounjaro have been licensed only recently. All 3 medications have been specifically tested and approved to aid with weight loss.

Other injections can be prescribed as an ‘off-label’ treatment. Off-label prescribing allows a GP to prescribe medication if they think a patient could benefit from it, even if this is not the primary use.

Weight loss injections that have not been licensed include Ozempic, and Victoza. The table below shows each weight loss medication in more detail.

Wegovy Saxenda Ozempic Mounjaro Victoza
Active ingredient(s) Semaglutide Liraglutide Semaglutide Tirzepatide Liraglutide
Dosage Gradually increases until the maintenance dose of 2.4mg Gradually increases until the maintenance dose of 3mg Gradually increases until the maintenance dose of 1mg Gradually increases to a maximum dose of 15mg Gradually increases to a maximum dose of 1.8mg (for diabetes only)
What it's approved for Weight loss Weight loss Treating and managing type 2 diabetes Treating and managing type 2 diabetes or weight loss Treating and managing type 2 diabetes
How to take it Pre-filled injectable pen, self-administered Pre-filled injectable pen, self-administered Pre-filled injectable pen, self-administered Pre-filled injectable pen, self-administered Pre-filled injectable pen, self-administered
When to take it/Frequency Once a week Once daily, at the same time Once a week Once a week Once a day
Effectiveness* 83.5% after 68 weeks 63.5% after 68 weeks 66.9% after 24 months 96.3 % after 72 weeks 40.4% at 56 weeks
Is it prescription only? Yes Yes Yes Yes Yes
* percentage of people that lost 5% or more of their initial body weight

How do weight loss injections work?

All weight loss injections work in a similar way, depending on which active ingredient is used (liraglutide, semaglutide, or tirzepatide).

Liraglutide is a GLP-1 (glucagon-like peptide 1) agonist. It attaches to GLP-1 receptors, mimicking the hormone. By doing this, it controls hunger levels so you eat less without feeling hungry throughout the day. It also delays the emptying of your stomach, which helps you feel fuller for longer.

Semaglutide also works by mimicking GLP-1. This affects the parts of your brain responsible for hunger, sending a signal to your brain that you are full. It also controls blood sugar levels, which helps with cravings.

Tirzepatide is a GLP-1 agonist, meaning it works the same way as liraglutide and semaglutide by controlling hunger levels and cravings. It also imitates GIP (glucose-dependent insulinotropic peptide), a hormone released in the small intestine. This can improve how your body breaks down fat and sugars.

How effective are weight loss injections?

Weight loss injections are effective when used alongside an exercise and diet regime. For instance, this study found that once-weekly semaglutide injections, such as Wegovy, can sustain and reduce body weight alongside lifestyle changes.

  % of people who lost 5% of their body weight (dosage: standard or maintenance dose)
Diet and exercise alone 16.8 %
Saxenda 63.5 % (in 56 weeks)
Wegovy 83.5 % (in 68 weeks)
Mounjaro 96.3 % (in 72 weeks)

All information in this table has been sourced from clinical trials

How quickly will you see results?

You should start seeing results within a few weeks of starting to take weight loss injections and get the best effect with long-term use (12 weeks or more).

Your doctor will check your weight 12 weeks after you reach the maintenance dose. You should expect to see a weight loss of 5% or more of your initial body weight. Your doctor will stop the treatment and may suggest an alternative if you haven’t reached a 5% loss.

Which weight loss injection is the most effective?

Weight loss injections work differently depending on the person, they all have given good results in clinical trials so far. But this does not mean that they will be the most effective for you, or your needs.


In clinical trials the average weight loss of patients using 15mg Mounjaro weekly for 72 weeks was almost 24 kg. The medication has been shown to help 96% of its users lose at least 5% of their starting weight. Mounjaro is relatively new in the UK, but multiple studies show it’s safe and effective to use.


63.5% of people using Saxenda for 56 weeks or more lost at least 5% of their body weight. The average weight loss was 8.4kg. Several clinical trials have shown that Saxenda (liraglutide) is a safe and effective treatment for weight loss.


Wegovy has been found to achieve 5% or more initial body weight loss for up to 83.5% of patients after 68 weeks of use. Since its approval in 2023 many patients have used it safely and with good results.


Ozempic is not approved for weight loss in the UK – but Wegovy contains the same active ingredient and is formulated for weight loss specifically. Clinical trials testing Ozempic for its actual purpose, managing type 2 diabetes, have found a weight loss of 4.5 kg on average after using 1mg Ozempic for 30 weeks.

Weight loss injections vs pills

All weight loss injections and most weight loss pills are prescription only, with a few exceptions. The weight loss pills currently available include:

  • orlistat (prescription-only): An unbranded tablet containing the active ingredient orlistat. Each tablet helps your body to excrete around a third of the fat eaten with each meal instead of digesting it.
  • Xenical (prescription-only): A branded version of orlistat, working in the same way and allowing you to lose weight when taken with meals containing fat.
  • Mysimba (prescription-only): A tablet containing bupropion and naltrexone hydrochloride, which work on the areas of your brain controlling hunger and energy levels.
  • Alli (over-the-counter medication): Also contains the active ingredient orlistat but in a lower dose than prescription orlistat and Xenical.

Which is more effective?

Both injections and pills can help with weight loss, but injections like Wegovy and Mounjaro may be most effective in the long term.

Tablets containing orlistat are only effective if you reduce your fat intake with each meal and can only be taken with meals containing fat.

Mysimba has a similar effect on the brain as weight loss injections, as it helps control appetite and hunger. In one study, Mysimba helped people lose weight, but there was a higher risk of side effects. For people who experience side effects, injectable weight loss treatments may be preferred. If you aren’t comfortable with injections, this might be a good option to try, though.

  % of people who lost 5% of their body weight (dosage: standard or maintenance dose)
Diet and exercise alone 16.8 %
Mysimba 62 % (in 56 weeks)
Orlistat 37 % (in 24 months)

All information included in this table has been sourced from clinical trials.

Are side effects different?

Yes, side effects can vary between weight loss injections and pills. Common weight loss injection side effects include nausea (feeling or being sick) and vomiting, headaches, diarrhoea, or constipation. Mysimba has some similar side effects.

Weight loss pills containing orlistat have different side effects because they affect fat digestion rather than the brain. Common orlistat, Xenical, and Alli side effects include fatty or oily stools, diarrhoea, and flatulence (farting).

Always read the patient information leaflet before starting any new drug, and contact a doctor if you develop side effects which you’re concerned about.

  Weight Loss Injections Weight Loss Pills
Nausea and vomiting (feeling or being sick) x  
Headaches x  
Diarrhoea or constipation x x
Fatty or oily stools   x
Flatulence (farting)   x

Are weight loss injections safe?

Yes, weight loss injections are a safe treatment option. Your doctor will check your medical history and medications to make sure your chosen treatment option is suitable.

In this study, patients who used semaglutide for 2 years noticed substantial weight loss with only mild to moderate stomach upset.

The benefits of using weight loss injections to achieve a healthy weight often outweigh the mild to moderate side effects some patients experience. You can manage side effects at home, which usually improve as you continue your treatment.

Can I use weight loss injections if I’m pregnant or breastfeeding?

Weight loss injections are not recommended if you are pregnant or breastfeeding. It is not known if the medication in weight loss injections can be passed onto your baby. More research needs to be done into this.

What are the side effects of weight loss injections?

Very common side effects of weight loss injections include:

  • nausea or vomiting
  • diarrhoea or constipation

Common side effects of weight loss injections include:

  • low blood sugar
  • dry mouth
  • pain, itching, irritation, or swelling at the injection site
  • gallstones
  • headaches
  • tiredness or weakness
  • a change in taste
  • heartburn or indigestion
  • bloating
  • wind
  • dizziness

Uncommon side effects of weight loss injections include:

  • skin rash
  • feeling unwell
  • dehydration
  • inflamed gallbladder
  • increased heart rate

If you notice these side effects, see if you can manage them at home. You should speak to your doctor if your side effects are severe or are not getting better after several weeks of treatment.

There are some rare but serious side effects to look out for when taking weight loss injections. If they happen, call 999 straight away or get someone to take you to A&E.

Rare side effects of weight loss injections include:

  • pancreatitis, which is an inflammation of the pancreas causing symptoms like nausea, vomiting, and severe stomach pains that do not go away
  • severe allergic reaction (anaphylaxis), which causes symptoms like difficulty breathing, swelling of the face, skin rash, and dizziness

Your dosage will be increased over several weeks to reduce the risk of side effects. If you get side effects, these will likely be mild and not bother you as much. You can manage side effects at home, as you usually would if you felt nauseous or constipated.

Which weight loss injection has the least side effects?

Side effects can vary from person to person. This is because some people may react differently, or even not at all, to the active ingredients in particular medications. For this reason, it's not possible to say that one weight loss injection has fewer side effects than another. Instead, the focus should be on finding a treatment that works for each individual person.

Where can I buy weight loss injections?

If you meet the criteria for weight loss injections, you can order them online through Superdrug Online Doctor. You can also get some weight loss injections through the NHS. There are no over the counter weight loss injections.

Can you buy weight loss injections online?

Yes, through trusted and regulated online doctor services like Superdrug Online Doctor. This works just like your GP, except you don’t need to make an appointment or wait for a referral. Simply complete a short online form, which will be sent to one of our doctors.

A doctor will prescribe the medication if you are suitable for weight loss treatment. Your medication will be sent to your home in discreet packaging or you can collect it at your local Superdrug pharmacy.

Can you get weight loss injections over the counter?

No, weight loss injections contain active ingredients that should only be prescribed by a doctor.

Can you get weight loss injections on the NHS?

Yes, you can get weight loss injections on the NHS. You will usually need to be referred to a weight management specialist who might try other treatment options before suggesting weight loss injections.

How can I get a prescription for a weight loss injection?

To be suitable for weight loss injections, you need to have:

a BMI (body mass index) of between 27 and 30 kg/m² (overweight) and a weight-related health condition, such as high blood pressure or diabetes

a BMI of greater than 30 kg/m² which is classed as obese

Guidelines also state that patients must follow a health and exercise plan set out by their doctor or a weight management specialist.

You cannot use a weight loss injection if you:

  • are allergic to the active ingredient, or any other ingredient in the injection
  • have severe heart failure
  • are over 75 years old* (there is not enough research into the use of weight loss injections at this age)
  • are already taking a similar medication for the management of type 2 diabetes
  • are pregnant or breastfeeding

*this does not apply to Wegovy

You should speak to your doctor if you take any medication, especially blood thinners like warfarin or other diabetic treatments.

People with kidney, pancreas, heart, liver, or thyroid problems should speak to their doctor before using a weight loss injection.

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