Easy. You set up a double-blind experiment in which the constituents of a random sample of the population are randomly assigned to one of two groups: experime

Easy. You set up a double-blind experiment in which the constituents of a random sample of the population are randomly assigned to one of two groups: experimental group or control group. You administer the experimental group the new drug (dammit, now I've got Huey Lewis and the News stuck in my head...), while the control group gets a placebo. You then administer both groups further placebos, and measure their response to those placebos.