Sun Pharma, India's largest drugmaker, has underperformed the Sensex and Nifty for the first time in six years, with its stock declining approximately 8% while indices rose nearly 9%. This underperformance is attributed to weaker US business momentum, increased competition in generics, sustained pricing pressure, unfavorable currency movements, and ongoing regulatory scrutiny. Analysts anticipate minimal contribution from key products and note that higher R&D spending and operating costs continue to impact performance.