If an acquisition happens, it would give Valeant an array of other cosmetic and eye drugs and add to a string of more than 50 acquisitions that have made it one of Canada's largest drugmakers.
Each Allergan share would be exchanged for $48.30 in cash and 0.83 shares of Valeant Pharmaceuticals International Inc. common stock. Shareholders can choose a mix of cash and stock. Allergan stockholders would own 43 percent of the combined company.
In pre-market trading, shares of Valeant spiked by more than five percent, while Allergan's stock skyrocketed by more than 17 percent.
Ackman's Pershing Square Capital Management LP -- Allergan's biggest stockholder at 9.7 percent -- has agreed to take only stock in the transaction and plans to continue as a long-term shareholder of the combined company.
Valeant Chairman and CEO J. Michael Pearson said in a statement that Allergan CEO David Pyott and the company's board have made it clear that they don't want to have talks about a potential combination. But Pearson said he's hoping that the offer being put on the table will enable the two sides "to engage in productive discussions."
On Monday Allergan said in a statement that if it received an offer that its board -- along with financial and legal advisers -- would evaluate it.
Valeant, which is based in Laval, Quebec, said Tuesday that it anticipates the proposed Allergan deal resulting in more than $2.7 billion in annual cost savings.
Allergan, based in Irvine, Calif., has long been considered one of the star performers in the specialty pharmaceutical sector. "Specialty pharmaceutical" is an industry term that differentiates smaller drugmakers from much bigger companies that sell a wide array of drugs, such as Pfizer and Merck.
Allergan reported revenue of $6.3 billion last year, up 12 percent from 2012. The company's growth has been driven by expanding use of its blockbuster product, Botox, combined with a broad offering of eye care drugs, skin care formulas and breast implants.
Last year Botox sales rose 12 percent to nearly $2 billion. First introduced in 1989, the injectable drug is most famous for its ability to smooth wrinkle lines on aging foreheads. But over the years Allergan has racked up more than a half-dozen other approved uses for Botox, including treatment for neck spasms, eye muscle disorders and migraine headaches.
Allergan's shares jumped more than 18 percent in premarket trading. Valeant's stock rose more than 7 percent.
Valeant also announced Tuesday that it is raising its full-year earnings forecast to $8.55 to $8.80 per share, up from $8.25 to $8.75 per share. It's also boosting its revenue guidance to a range of $8.3 billion to $8.7 billion. Previously the company predicted revenue of $8.2 billion to $8.6 billion.
Analysts surveyed by FactSet expect 2014 earnings of $9.63 per share on revenue of$9.35 billion.
--By The Associated Press