Amycretin vs tirzepatide: comparing a future candidate with a licensed medicine

Tirzepatide: a completed phase 3 programme and a UK licence

Tirzepatide (brand name Mounjaro) is a dual GIP and GLP-1 receptor agonist made by Eli Lilly. It activates two gut-hormone pathways simultaneously, a mechanism no other licensed UK weight-loss injection shares. In the SURMOUNT-1 trial, published in the New England Journal of Medicine, adults with obesity taking tirzepatide 15mg for 72 weeks lost an average of around 20–21% of body weight. The trial randomised 2,539 participants; that is the evidence base the MHRA and NICE assessed when granting UK approval. NICE's appraisal, TA1026, recommends tirzepatide for eligible adults with a BMI of 35 or above alongside at least one weight-related condition, with lower BMI thresholds for certain ethnic backgrounds. Treatment starts at 2.5mg (a tolerability dose that gives your system time to adjust) and is titrated upward by the prescriber. The medicine is dispensed on a private prescription by a GPhC-registered pharmacy. Mounjaro is also the only licensed dual-agonist weight-loss medicine available in the UK, a fact worth holding onto when reading coverage of newer candidates, and if you are curious about the relationship between the molecule and the brand, our page on tirzepatide vs Mounjaro explains how the two names refer to the same approved treatment.

Amycretin: early phase 1 signal, no UK approval

Amycretin, developed by Novo Nordisk, is a single molecule designed to combine amylin and GLP-1 receptor agonism. Phase 1 trial data reported in 2024 showed average weight loss of around 13% over 12 weeks in a small cohort — an unusually strong short-term signal for an early-phase compound. That figure attracted significant press coverage. A common misconception in those reports was that amycretin had already outperformed every existing treatment; at 12 weeks in a phase 1 safety study, against a mature 72-week phase 3 dataset, the comparison simply does not hold in any straightforward way. Twelve weeks of amycretin data and 72 weeks of tirzepatide data are measuring different things over different timeframes. Amycretin has no UK licence, no approved dosing schedule, no completed phase 3 programme, and is not available through any UK pharmacy. The NHS medicines information for tirzepatide gives context on the licensed product; amycretin does not yet have an equivalent regulatory record to cite.

Side-effect profiles: what is and is not yet known

Tirzepatide's tolerability profile is well characterised across thousands of trial participants and real-world prescribing. The most common side effects are gastrointestinal: nausea, loose stools, constipation, reflux and reduced appetite are all documented. They tend to be most noticeable after starting or after a dose increase, and for many people they ease within the first couple of weeks at a new level. The January 2026 MHRA Drug Safety Update flagged acute pancreatitis as an infrequent but serious risk across GLP-1 medicines; severe abdominal pain radiating to the back warrants urgent medical attention. For amycretin, phase 1 data reported GI-predominant side effects consistent with GLP-1 agonism, but the dataset is small and the long-term profile is genuinely unknown. When a medicine has not cleared phase 3, its rarer adverse events have not had the statistical exposure to surface reliably. That asymmetry is not an argument against amycretin's future, but it is a reason the comparison on safety is inherently one-sided at this stage.

What this means for someone looking at treatment now

If you are considering weight-loss treatment in the UK today, amycretin is not an option at any pharmacy, regulated or otherwise. Tirzepatide is licensed, dispensed by GPhC-registered pharmacies, and has a full evidence base. You can read about Mounjaro and how it works, explore how tirzepatide compares to standard GLP-1 medicines, or see what the experimental compound retatrutide looks like against tirzepatide for a sense of the broader pipeline. For cost context, Mounjaro pricing is explained on its own page. Some people also ask whether Manjaro is a different product, and our page covering tirzepatide vs Manjaro addresses that question directly. If the idea of a dual-mechanism injectable suits you, the conversation starts with a prescriber, not a comparison article. Our free consultation is reviewed the same day by a real clinician who can assess your health picture properly. Which treatment suits you is a clinical decision our prescribers make with you.