The deal had separately come under scanner of the market regulator Sebi for alleged insider trading violations and the present 'no-objection' from the exchanges.
Typically, CCI takes decisions related to M&As within 30 days, though it can do so within 210 days of the filing of application.
At 1130 hours, the Sensex was up 99 points at 22,260 and the 50-unit Nifty shed 26 points at 6,669 levels.
Sun Pharma and Ranbaxy Labs hogged the limelight after Sun Pharma announced the acquisition of Ranbaxy Labs.
Last week, the court had vacated the status quo order it had issued earlier on the merger process between Sun Pharma and Ranbaxy.
In a fresh round of patent battle over the launch of generic drugs in the US market, domestic pharmaceutical majors Orchid, Sun Pharma and Ranbaxy Laboratories have been sued by Cima Labs, Otsuka Pharmaceutical Co and Abbott Laboratories, respectivel
Sun-Ranbaxy are keen to complete the merger process.
Ranbaxy was asked to sell all products containing Leuprorelin which are marketed and supplied under brand name Eligard.
Based on a writ petition filed by some individual investors, the High Court while ordering the status quo on Friday, issued notices to SEBI, BSE, NSE, Sun Pharma, Ranbaxy, Daichii Sankyo and Silver Street Developers.
Shares of Ranbaxy Lab and Sun Pharma on Tuesday gained as much as 4 per cent after the drug-makers got CCI's approval for their long-pending $4-billion merger.
After a detailed scrutiny, fair trade watchdog CCI has suggested Sun Pharma and Ranbaxy to make certain changes in their proposed $4 billion merger deal, including possible divestment of some brands, to address anti-competitive concerns.
Silverstreet Developers LLP, which had no holding in Ranbaxy at the end of September 2013, had bought shares of the Gurgaon-based firm aggregating 1.41 per cent stake by end of December 2013. As on March 31, 2014, its holding stood at 1.64 per cent.
The year 2015 will be a tough year for mergers and acquisition.
India's antitrust regulator has approved Sun-Ranbaxy deal, subject to the companies divesting seven products.
It had posted net profit of Rs 125.75 crore (Rs 1.25 billion) during the January-March quarter of the previous fiscal, 2012-13.
Two individuals filed the petition in the high court of Andhra Pradesh
The group is looking into a new role for Ranbaxy CEO and MD Arun Sawhney.
Sun Pharma's offer was tempting because Ranbaxy was too busy fighting fires in the US to concentrate on operations.
The comments need to be submitted to the Competition Commission of India within 15 days, along with supporting documents on how the merger can adversely impact the concerned person or entity, the regulator said, while adding that it would not consider 'unsubstantiated objections' to the deal.
A source said the competition watchdog would by next month suggest 'structural remedies' that included selling key drug segments as conditions for clearing the country's largest pharmaceutical industry merger.
But splitting management bandwidth by investing in non-core businesses will not be appreciated by the market in the long run.
Sun Pharma would have to do a lot of work to get USFDA to revoke the ban on Ranbaxy facilities but it has not put any time-frame for this, company ChairmanIsrael Makov said.
It hopes to turn around Ranbaxy within four years of closing the deal by improving efficiency and resolving all regulatory issues
The Sensex ended down 251 points at 27,351 and the Nifty shed 65 points to close at 8,228.
Sensex plunges 322.39 points to over 1-month closing low of 27,797.01; Nifty tumbles 97.55 points to 8,340.70.
The 30-share Sensex ended 50 points lower at 28,112 and the 50-share Nifty declined 12 points to close at 8,531.
Torrent to buy Ranbaxy's anti-bacterial generic
The 30-share Sensex closed down 115 points at 28,444 and the 50-share Nifty ended down 31 points at 8,524.
Few top honchos of India Inc did very well in 2014.