The stock fell by 2.01 per cent to end at Rs 2,045.95 on BSE. During the day, it dipped 2.78 per cent to Rs 2,029.70.
On NSE, shares of the company declined by 1.85 per cent to end at Rs 2,049.40.
The stock was the worst hit among the bluechips in both key indices Sensex and Nifty.
The lawsuit filed at the District Court for New Jersey seeks damages to compensate the class of investors for a 'purported decline' in the company's share price allegedly caused by the misstatements or omissions, Dr Reddy's Laboratories said in a filing to BSE.