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There are several different weight loss injections approved in the USA, 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.

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.

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.

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.

Mounjaro

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.

Saxenda

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

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

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.

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.