Randomized controlled trial

A randomized controlled trial is a study that randomly assigns participants to a treatment group or a comparison group. That random assignment is what makes it the strongest design for showing whether a treatment actually causes an effect.

Definition from Shrinktionary, reviewed by Shariq Refai, MD, MBA, FAPA (last reviewed 2026-06-26). Shrinktionary is the network's language layer and carries the canonical short definition; this page adds the research-context detail below. Full definition on Shrinktionary →

The word "random" is the important part. A computer, not a researcher, decides which group each person joins. This matters because it spreads out the things that could tilt the result, such as age, how severe someone's anxiety is, or whether they have other health problems. When the groups start out alike, a difference at the end is more likely to come from the treatment itself.

Most of what we know about anxiety treatments comes from RCTs. When a guideline calls a therapy or a medication "first-line," that ranking usually rests on a stack of RCTs. A study that isn't randomized can still be useful, but it can't rule out the chance that the groups were different before anything started.

A trial of cognitive behavioral therapy for panic disorder might enroll 200 people. A computer assigns half to start CBT now and half to a waitlist. After twelve weeks, the researchers compare panic attack counts between the two groups.

A single RCT is one data point. Small size, short follow-up, and a weak comparison group, such as a waitlist instead of a real alternative treatment, all limit how much weight a trial deserves. A treatment looks strongest when several solid RCTs point the same way.