The drugmaker AbbVie said on Tuesday that it planned to buy Allergan, the maker of Botox, for about $63 billion, in one of the biggest mergers in the health care industry this year.

The deal represents a classic response to a perennial drug industry challenge: how to recover when a blockbuster drug is losing its patent protection. In acquiring Allergan, AbbVie gets to bypass the risky process of research and development by buying a portfolio of popular products as it faces the loss of patent protection for Humira, a treatment for rheumatoid arthritis that is the world’s top-selling drug.

“This is the age of blockbusters,” said David Maris, an analyst for Wells Fargo who follows the drug industry. “And when blockbusters start to go away, companies don’t have too many things they can do.”

The deal is the second-biggest takeover in the pharmaceutical industry announced this year, after Bristol-Myers Squibb agreed to buy Celgene, a maker of anticancer drugs, for $74 billion, against the backdrop of the health care industry’s mounting interest in such deals.