** Sun Pharmaceutical Industries SUN.NS down 4.8% to 1,635 rupees; set for worst day since August 31, 2020

** Stock top loser on benchmark Nifty 50 .NSEI, Nifty 500 .NIFTY500 indexes

** Sun Pharma has decided to proceed with binding offer of $12 billion to acquire U.S.-based Organon OGN.N, newspaper The Economic Times reports, citing sources

** ICICI Securities says deal would value OGN at ~2x its 2026 expected sales when it's facing competition across three operating segments of women's health, biosimilars, established brands

** Adds SUN expected to assume $8 billion debt (as part of deal)

** Notes prime facie, target seems to be fraught with challenges

* Both cos yet to respond to Reuters email seeking comment

** More than 4.7 million SUN shares traded, ~1.6x the 30-day avg vol

** SUN rated "buy" on avg; median PT at 1,978 rupees, per data compiled by LSEG

** YTD, SUN down 5%