(Bloomberg Business) -- Please open your stock-market playbook to the chapter on defensive industries, and flip to the page about health-care stocks. Now, rip that page out and throw it away.

The old playbook has always treated stocks of drugmakers and health insurers as the place to turn when times get tough. The idea is that, theoretically, people will continue to buy the medicine they need long after they've stopped splurging on new clothes or a new car or even a night out on the town.

As a result, health-care stocks tended to perform better than other industries during bear markets. But a funny thing happened over the last few years of the latest bull run: health-care stocks outperformed by a long shot, including a market-leading advance of 12 percent so far this year.