Real‐World Treatment Patterns and Weight Outcomes Before and After a Tirzepatide Price Increase in Over One Million Self‐Paying UK Adults With Overweight or Obesity

AIMS: Glucagon-like peptide-1 (GLP-1) receptor agonist-based medicines are highly effective treatments for overweight and obesity, but population-scale real-world evidence remains limited, particularly in self-funded settings where treatment choice may be influenced by relative price. We aimed to characterise provider reach and treatment patterns through a large United Kingdom (UK) telehealth provider, assess changes around the September 2025 tirzepatide list-price increase of up to 170%, and estimate longitudinal weight trajectories. MATERIALS AND METHODS: A retrospective cohort study of adults initiating semaglutide or tirzepatide through MedExpress from 1 May 2024 to 1 January 2026 was conducted. Treatment initiation and switching were analysed using segmented interrupted time-series models, with sensitivity analyses addressing anticipatory changes in August 2025. Weight trajectories were estimated using linear mixed-effects models. RESULTS: Among 1 033 522 adults, 932 659 (90.2%) initiated tirzepatide and 100 863 (9.8%) semaglutide; provider reach was higher among women than men. In September 2025, semaglutide initiation increased by 31.15 percentage points (95% CI: 26.07-36.24) relative to the projected pre-interruption trend. Tirzepatide-to-semaglutide switching increased by 9.26 percentage points (95% CI: 7.09-11.42) and subsequently attenuated. Sensitivity analyses supported anticipatory changes in August. At 12 months, estimated weight loss was 19.93% with tirzepatide (95% CI: 19.88-19.98; n = 30 763) and 16.40% with semaglutide (95% CI: 16.16-16.64; n = 979). CONCLUSIONS: A single UK telehealth provider achieved substantial reach among adults with overweight or obesity. Treatment initiation and switching changed markedly around the tirzepatide price increase. Substantial longitudinal weight loss was observed among patients contributing follow-up in the context of limited adjunctive lifestyle support.