Shares in Novo Nordisk plunged more than 16% after clinical trial data showed its latest obesity injection delivered weaker results than a comparable treatment from its American competitor, Eli Lilly. The figures rattled investors who had been counting on the new therapy to reinforce the Danish group’s dominance in one of the most profitable corners of the pharmaceutical industry.

Novo’s stock has been sliding since 2024, as Lilly steadily expanded its foothold in the booming market for weight-loss medicines, drawing patients and prescriptions away from its Scandinavian rival. Analysts say the latest data deepen concerns that Novo’s pipeline may struggle to match the clinical performance and commercial momentum of Lilly’s flagship products.

The setback complicates Novo’s efforts to restore market confidence and regain lost ground in a sector where small differences in efficacy can translate into billions in revenue.