Eli Lilly and Novo Nordisk are confronting a new challenge to their dominance in the fast-growing weight-loss drug market: mounting pressure from generic manufacturers that could bring copycat competition sooner than expected.

The issue centers on the companies’ blockbuster treatments, which have fueled surging sales and reshaped the obesity drug market. As patent timelines, legal disputes and manufacturing strategies come under scrutiny, rivals are exploring ways to challenge that market control earlier than analysts had forecast.

For both drugmakers, the prospect of cheaper alternatives could eventually reshape pricing, margins and access for patients. The latest developments underscore how quickly the competitive landscape can shift in one of the pharmaceutical industry’s most valuable segments.

Investors are watching closely for signs of how the companies will defend their products, while generic makers weigh the commercial and legal hurdles involved in entering a market that remains highly lucrative and tightly contested.