Under the deal, Plethico plans to buy all outstanding shares of Natrol for $4.40 each in a tender offer to start Nov. 27, the companies said in two separate statements on Monday.
"We are looking at another acquisition in the U.S.... which has a manufacturing facility and a great set of brands," Sanjay Pai, Plethico's chief financial officer, said.
"We are trying to consolidate in this nutraceutical sphere and are planning to become a big player in this segment."
The nutraceutical market in the U.S. is worth about $22 billion, he added.
Plethico shares, which jumped nearly 9 percent to a new high of 507.7 rupees, are now up 6 percent at 494.25 rupees.
Natrol's revenue, $65.6 million in 2006, is expected to rise to $90 million in 2009 with contributions from the three acquisitions it made in the last 12 months, Wayne Bos, president and chief executive officer of Natrol said.
Last year, the U.S. firm's net profit was marginally above break-even, he added.
Plethico would fund the deal through the $75 million it raised in convertible bonds and the rest would come from the proceeds from its initial public offering, Pai said.
Plethico, which made its stock market debut last May, got more than half its revenue from nutraceuticals and herbal products in 2006/07, he added.