Combination Drugs

For pharmaceutical companies, combination products look like a relatively low-risk way to create a new product, one that can also extend the life of a patent-expiring compound. They can be good business: according to IMS Health, combination drugs introduced in the past four years generated almost $10 billion in sales in the US in 2003. More and more combination products are in pharma's pipeline and coming to market. Some of these drugs do well, but many don't. Why?