The short answer
In the simplest clinical trial design, the control group receives the standard, already-approved treatment, while the investigational group receives the new treatment being studied. Researchers compare the groups during and at the end of the trial to see which is more effective or has fewer side effects. Placebos are rarely used as the control.
In the simplest trial design, there are two groups: investigational and control.
The investigational group receives the study intervention or drug.
The control group usually receives the standard, already-approved treatment, not a placebo.
Researchers compare the groups at several points during and at the end of the trial.
Choose how you want to understand this
The full explanation.
The basic two-group setup
Many cancer clinical trials, especially in later phases, use a simple structure built around two groups. Understanding how these groups work can make the whole idea of a clinical trial feel less abstract.
In the simplest version of this design, participants are split into an investigational group and a control group.
What each group receives
The investigational group receives the study intervention or drug — the new approach being tested in the trial. The control group receives the standard treatment, meaning the treatment already established and approved for that type of cancer.
This setup gives researchers something to measure against. Without a control group, there'd be no clear way to know whether a new treatment is actually better, worse, or about the same as what's already available.
How the comparison happens
Researchers don't wait until the very end of a trial to look at results. Instead, they compare the investigational and control groups at several points during the study, as well as at its conclusion. These comparisons look at things like how effective each approach is and whether one group experiences more or fewer side effects than the other.
This ongoing comparison is part of what allows a trial to be stopped early if needed — if the difference between the groups becomes clear well before the trial's planned end date.
Where randomization fits in
In phase 3 trials, participants are typically assigned to the investigational or control group through randomization — meaning the assignment happens by chance rather than by choice. This matters because it helps ensure that any difference in outcomes between the groups reflects the treatment itself, rather than differences among the people who happened to end up in each group.
Randomization and control groups work hand in hand: randomization determines who ends up where, and the control group provides the baseline that the investigational group gets compared against.
Placebos rarely enter the picture
It's a common assumption that a control group automatically means receiving a placebo — an inactive treatment with no real effect. In cancer trials, that's usually not the case. Placebos are rarely used in cancer treatment trials. Instead, the control group most often receives the standard treatment already used for that cancer, meaning participants in the control group are still receiving real, established care.
Why this matters if you're considering a trial
Knowing how a trial's control group works can shape how you think about joining. If you're assigned to the control group, you're not being left without treatment — you're receiving the treatment currently considered the best available option, while contributing to research that could improve care for future patients. If you're assigned to the investigational group, you're getting access to a new approach that researchers believe has a reasonable chance of being at least as good, evaluated under close observation throughout the study.
Either way, being part of a trial means being part of a carefully monitored comparison designed to answer a real question about what works. Ask your care team what the control group in a specific trial receives before you decide whether to join — the answer is one of the clearest ways to understand what being part of that study would actually look like for you.
Words to know
Tap any term to see what it means.
Common questions
▸What does the control group receive in a clinical trial?
In the simplest trial design, the control group receives the standard treatment already approved for that type of cancer, while the investigational group receives the new study intervention or drug.
▸How are the two groups compared?
Researchers compare the investigational and control groups at several points during the trial and again at the end, to see which is more effective or has fewer side effects.
▸Does the control group get a placebo?
Usually not. Placebos are rarely used in cancer treatment trials. The control group usually receives the standard, already-approved treatment instead.
▸Why does the control group matter?
Without a control group, researchers wouldn't have a fair comparison to know whether a new treatment is actually better than what's already available.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Test your knowledge
0 of 3 answered
This quiz checks understanding of educational content only. It is not medical advice. Open this quiz on its own page.
How this page was created
Cancer Explained uses AI to organize and translate information from the authoritative sources cited on each page. Automated checks review claims, citations, clarity, duplication, and potential safety concerns before publication. Our content is not currently reviewed by physicians unless a specific qualified reviewer is named on the page. Cancer Explained provides general education and should not replace advice from your healthcare team.
Editorial status: Source verified — This page was created with AI assistance and checked against the sources listed on it. Source checking is not a medical review.
Human medical review: not completed. At this time, most Cancer Explained content has not been reviewed by a physician or other healthcare professional. Pages with documented human medical review identify the reviewer, credentials, and review date directly.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.