After a negative opening on BSE, the stock further shed 3.08 per cent to Rs 418. At 1330 hrs, the stock was trading at Rs 424.65, down 1.54 per cent.
Similarly, on NSE, the scrip declined 3.11 per cent to Rs 418.
When asked about the whistleblower complaint against Sun Pharma, Sebi Chairman Ajay Tyagi told reporters on Wednesday: "There is a whistleblower complaint which we are examining. I have nothing more to add."
A whistleblower had last month approached Sebi with a document alleging various irregularities by the company, its promoter Dilip Shanghvi and others.
Shanghvi, who is also the managing director of the pharma firm, earlier this month denied receiving any query so far from the markets regulator regarding the whistleblower complaint.
In August 2017, Sun Pharma, Shanghvi and nine other entities settled an insider trading probe on payment of Rs 18 lakh towards settlement charges.