The business of clinical trials is booming. Private equity has taken notice.

After finding success investing in the more obviously lucrative corners of American medicine — like surgery centers and dermatology practices — private equity firms have moved aggressively into the industry’s more hidden niches: They are pouring billions into the business of clinical drug trials.

To bring a new drug to market, the FDA requires pharmaceutical firms to perform extensive studies to demonstrate safety and efficacy, which are often expensive and time-consuming to conduct to the agency’s specifications. Getting a drug to market a few months sooner and for less expense than usual can translate into millions . . .