June 23 (Reuters) - Allergan Inc on Monday advised investors not to sell their shares to Valeant Pharmaceuticals International which launched a hostile takeover offer for the California-based Botox maker last week, saying it was "grossly inadequate."

Allergan said its advisors Goldman Sachs & Co. and BofA Merrill Lynch told the board on June 21 the offer was inadequate from a financial point of view.

The recommendation was consistent with Allergan's previous rejections of Valeant's $52 billion cash and stock offer. The Canadian company and activist investor William Ackman, who owns nearly a 10 percent stake in Allergan, made a joint bid to acquire the company in April.

Allergan said in a statement that because of Valeant's declining share price, the offer is now worth about $173.20 per share, down from the $179.25 per share it reached on May 30.

It said that the offer undervalues its "industry-leading position, financial performance, strong balance sheet, exceptional management and growth prospects." Allergan reiterated its goal to increase adjusted earnings by 20 to 25 cents per share and generate $14 billion in free cash flow in the next five years.

(Reporting by Caroline Humer; Editing by Sofina Mirza-Reid)