The stock dropped 4.80 per cent to settle at Rs 3,336.30 on BSE. Intra-day, it lost 5.72 per cent to Rs 3,304.
On NSE, shares of the company plunged 4.86 per cent to end at Rs 3,330.70.
The stock has fallen by over 20 per cent in three days, with market valuation down by Rs 15,630.55 crore at Rs 56,913.45 crore.
Dr Reddy's CEO G V Prasad also said the company is in the process of shifting some of the products to other plants in the wake of the warning letter.
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"We have instituted corrective actions to assess the 483 observations received earlier for these sites. The recent letter underscores the need for us to reevaluate the work done in light of the observations (made by the FDA) and continue to implement the process...
The country's second-largest drugmaker last week said it received a warning letter from the US drug regulator relating to two of its active pharma ingredients (API) manufacturing plants and a formulation plant.
In the broader market, the BSE 30-share Sensex plunged 378.14 points to end at 25,743.26.