How Long Have Weight Loss Injections Been Around?

Where the science actually started, and why it took so long to reach weight management

The GLP-1 hormone was identified in the 1980s, but turning that biology into a stable, injectable medicine took years of chemistry. Early GLP-1 receptor agonists were approved for type 2 diabetes in the mid-2000s, not weight management. Researchers noticed something significant: patients using these medicines as diabetes treatment also lost meaningful body weight. That observation became the starting point for dedicated obesity trials.

Semaglutide at the higher 2.4mg weekly dose was investigated specifically for weight management in the STEP programme, with STEP 1 published in the New England Journal of Medicine in 2021. Participants without diabetes lost around 15% of their body weight on average over 68 weeks, a result that had not been achieved by an injectable medicine in that population before. That trial involved over 1,900 adults and was placebo-controlled. It was not a small study or a short one.

Tirzepatide, a dual GIP and GLP-1 receptor agonist, built on this foundation with the SURMOUNT programme. SURMOUNT-1, also published in the New England Journal of Medicine, randomised 2,539 adults and ran for 72 weeks. The average weight reduction at the highest dose was around 20 to 21%. If you are trying to decide whether there is meaningful evidence behind these medicines, the trial scale and duration give a clear answer: yes. You can read more about how long weight loss injections take to work to understand what that evidence means in practice.

What changed between the diabetes versions and the obesity-licensed medicines you can access today

The diabetes versions of semaglutide (Ozempic) and tirzepatide (Mounjaro in its diabetes licence) use different doses and were approved for a different clinical purpose. The weight-management licences required separate trial programmes at higher doses, in different populations, with different primary endpoints. This is not a trivial distinction. The MHRA does not grant a weight-loss licence on the back of diabetes data alone; dedicated trials are required.

Wegovy (semaglutide 2.4mg) received its UK weight-management licence in 2021. Mounjaro's weight-management licence in the UK followed in late 2023. Both carry the Black Triangle symbol, meaning the MHRA requests that healthcare professionals and patients report any suspected side effects through the Yellow Card scheme, supporting ongoing safety monitoring. That is standard practice for recently licensed medicines, not a signal of unresolved risk.

More recently, the class has continued to develop. A 7.2mg semaglutide pen for Wegovy was approved in April 2026, and oral semaglutide tablets (Wegovy) received MHRA approval for weight management in June 2026. The overview of weight loss injections covers the current licensed options in more detail.

What this history means for someone deciding whether to start treatment now

Deciding to start a weight loss injection is not the same as deciding to try something experimental. By the time Mounjaro or Wegovy reaches you through a regulated UK pharmacy, it has been through phase 3 trials involving thousands of participants, regulatory review by the MHRA, and in most cases a NICE appraisal. The NICE appraisal of tirzepatide (TA1026) assessed the full evidence base before recommending it for use in England.

The more useful questions at this point are practical ones: does your BMI and medical history make you a suitable candidate, what does treatment actually involve week to week, and how long might you need to stay on it? Those are questions our prescribers work through with every patient, you can find general background on who weight loss injections are suitable for before you start a consultation.

One thing many people find reassuring when they first receive their prescription: the pen itself is a pre-filled, once-weekly injection with a fine needle, dispatched in plain unbranded packaging and tracked through DPD, so there is none of the drama the name "injection" might conjure. The practicalities of travelling with a weight loss injection, storage and day-to-day use are things our clinical team covers as part of aftercare.

If you are weighing how long you might need to stay on treatment, the duration guidance for weight loss injections and the separate question of how long you have to keep taking them are both worth reading. For a full picture of the options currently available, our guide to weight loss injections in the UK is a good starting point.

If you are ready to find out whether treatment is right for you, start your free consultation with our clinical team today, a named prescriber, not software, reads every submission the same day.