Inclusion & Exclusion Criteria

Scientist Explains with Dr. Tarek Rajji

May 27, 2021

The inclusion criteria for a clinical trial are carefully selected parameters used to include or recruit people into a study. Researchers may look for people with specific condition(s) (e.g., moderate to severe Alzheimer’s disease), ages, ethnicities, or other attributes to join their study. 

Clinical trials also have exclusion criteria. These are carefully selected parameters that researchers use to exclude or prevent people from joining their study. There are a number of reasons why researchers may have specific exclusion criteria. 

• Example of exclusion criteria based on condition(s): In clinical trials for people living with Alzheimer’s disease, a diagnosis of schizophrenia may be part of the exclusion criteria because this condition can itself lead to memory problems. This makes it difficult for researchers to know what is causing the memory problem and whether the treatment may be beneficial. Instead, people living with schizophrenia may look for studies with inclusion criteria of schizophrenia with or without memory problems. 
• Example of exclusion criteria for safety reasons: Clinical trials exclude people who also have conditions that make it unsafe for them to receive the treatment being tested. For example, in studies testing transcranial magnetic stimulation (TMS), people are often excluded if they have metal pieces in their head as the magnetic fields generated by TMS such may shift the pieces and cause harm to the participant.  
• Example of exclusion criteria based on medication(s): Clinical trials also exclude people who are taking medications that may prevent the treatment being tested from being effective. For example, anti-seizure medications may be part of the exclusion criteria for a clinical trial with brain stimulation. This is because these medications can alter the brain in a way that interferes with the effects of brain stimulation approaches such as TMS. By having these exclusion criteria, researchers can ensure that the outcomes of this study are due to the brain stimulation.