Eli Lilly's weight-loss and diabetes pill goes on sale in UK pharmacies from Monday, giving patients an oral alternative to the injections that have dominated the market.
Foundayo, also known as orforglipron, is available on private prescription after the Medicines and Healthcare products Regulatory Agency approved it earlier this month.
The UK is the first country in Europe to authorise the tablet for both weight management and type 2 diabetes.
It is licensed for adults with a body mass index of 30 or above, or between 27 and 30 with a weight-related condition, and can also improve blood sugar control in poorly managed type 2 diabetes.
Unlike some existing oral treatments, Foundayo can be taken at any time of day with no food or water restrictions.
The drug is not yet available on the NHS, with Lilly working with the National Institute for Health and Care Excellence on an assessment for wider rollout.
The launch lands as the US contest between Lilly and Novo Nordisk (NYSE:NVO), its main rival, shows little sign of easing.
A note from Citi found that Novo's Wegovy franchise held broadly flat in mid-August, up 3% week on week in the seven days to 14 August but flat on a four-week rolling average.
The bank's tracker showed Foundayo captured 36,620 US prescriptions in the same week, a 6% fall that followed a strong 14% gain the week before.
That compares with 137,333 for Novo's rival Wegovy pill in the equivalent 18th full week of its own launch.
Citi cautioned that the underlying trend remains hard to read given the volatility in the weekly data.
GLP-1 drugs mimic a gut hormone to curb appetite and have turned obesity treatment into one of the pharmaceutical industry's fiercest battlegrounds.
Pharmacists welcomed the UK launch but warned over a growing trade in fake and unlicensed GLP-1 tablets.
