“After careful review and consideration, our Board of Directors has unanimously determined that Valeant’s unsolicited proposal substantially undervalues Allergan,” said Allergan chief executive David E.I. Pyott.

Pyott said the board also determined Valeant’s proposal “creates significant risks and uncertainties” for his company’s shareholders and believes Valeant’s business model “is not sustainable.”

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Allergan’s statement comes after Bloomberg reported that the company had so far been rebuffed by rival companies it has tried to interest in making a competing offer, citing people familiar with the matter.

The statement also comes after Allergan enacted a one-year shareholder rights plan in April following Valeant’s takeover offer. Allergan said the move wasn’t intended to prevent an acquisition on terms it finds favorable, but instead was approved to give the board time to fully assess any proposals.

A shareholder rights plan, also known as a poison pill, is designed to dilute the value of the stock by flooding the market with additional shares, making it expensive for an investor to acquire a controlling stake.

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Canada-based Valeant, which generated $5.76 billion in revenue last year, in April disclosed its offer to acquire Allergan, at the time saying the deal would generate high single-digit organic growth for the foreseeable future, achieve more than $2.7 billion in annual operating cost synergies, and create a strong portfolio in opthalmology, dermatology, and aesthetics.

The Valeant takeover bid has already won support from Allergan’s largest shareholder, Bill Ackman’s hedge fund Pershing Square Capital Management LP. When the bid was announced, Pershing Square said it strongly supported the proposed combination.

Valeant spokeswoman Laurie Little said the company was “disappointed” Allergan had rejected the offer “without engaging in any substantive discussions with Valeant or Allergan’s largest stockholder, Pershing Square, and we remain committed to pursuing this transaction.”

But Allergan on Monday also struck a bullish tone about the company’s future results, saying it expects to increase per-share earnings by 20% to 25% and continue to generate double-digit revenue growth in 2015. The company also said it expects to produce double-digit sales growth and compounded annual profit growth of 20% over the next five years.