Clinical trial eligibility refers to the specific requirements a volunteer must meet to join a particular study. Every trial sets its own criteria, usually covering age, diagnosis, symptom severity, health history, and current medications. These requirements keep participants safe and help the study produce clear, reliable results.
Many people who look into research never find out why a study turned them away, or assume that one “no” means research is not for them. This guide explains what eligibility criteria are, why studies use them, which criteria come up most often in mental health research, and what you can do if you do not qualify. It also explains how eligibility screening works for volunteers at the Lehigh Center for Clinical Research in Lehigh County.
Key takeaways
Clinical trial eligibility is the set of requirements a person must meet to join a specific study. Inclusion criteria describe who a study is looking for, and exclusion criteria describe who cannot safely take part. Criteria differ from study to study, so not qualifying for one trial says little about whether you might qualify for another.
What Are Inclusion and Exclusion Criteria?
Inclusion criteria are the characteristics a person must have to join a study, such as a confirmed diagnosis or an age within a certain range. Exclusion criteria are characteristics that rule a person out, usually because they could make participation unsafe or make the results harder to interpret.
A volunteer has to meet every inclusion criterion and none of the exclusion criteria. Here is how the two might look for a hypothetical depression study:
| Example inclusion criteria | Example exclusion criteria |
| Age 18 to 65 | A history of bipolar disorder |
| A current diagnosis of major depressive disorder | Current use of certain medications that could interact with the study drug |
| Symptoms at or above a set score on a depression rating scale | An unstable medical condition, such as uncontrolled heart disease |
| Able to attend visits on the study schedule | Participation in another clinical trial within the past few months |
The public listing for a study usually shows only a handful of these requirements. The full list, which can run to dozens of items, lives in the study protocol and is reviewed with you during screening.
Why Clinical Trials Have Eligibility Criteria
Eligibility criteria exist first to protect people. A treatment that has not been fully studied could be riskier for someone with certain health conditions or someone taking a medication that might interact with it. Excluding those volunteers keeps them from taking on risks the study is not designed to monitor.
Criteria also help a study answer its question clearly. If participants vary too widely in diagnosis, severity, or other treatments, it becomes hard to tell whether changes came from the study treatment or from something else. A more consistent group makes the results easier to trust.
That consistency comes with a tradeoff, and researchers have studied it closely. A 2002 study in the American Journal of Psychiatry applied the criteria from 31 published antidepressant trials to 346 outpatients being treated for depression and estimated that only a small minority would have qualified. Common reasons included co-occurring anxiety or substance use, symptoms that were too mild, and a bipolar or psychotic form of depression. Findings like these are one reason many researchers now work to design criteria that reflect a wider range of real patients.
Common Clinical Trial Eligibility Criteria
While every study is different, most eligibility requirements fall into a few familiar categories:
- Age. Many adult studies enroll people between 18 and 65, though some focus on older adults, adolescents, or other groups.
- Diagnosis. Treatment studies usually require a confirmed diagnosis of the condition being studied, sometimes of a specific type or duration.
- Symptom severity. Studies often set a minimum or maximum score on a standard rating scale.
- Other health conditions. Certain medical or psychiatric conditions may be excluded for safety or to keep the study group consistent.
- Current and past medications. Some medications may interact with the study treatment. A study may also look at which treatments you have already tried.
- Lab results and vital signs. Blood work, blood pressure, or heart tests may need to fall within a set range.
- Pregnancy and family planning. Many medication studies exclude people who are pregnant or breastfeeding, and some require the use of birth control during the study.
- Recent research participation. Studies often exclude people who took part in another trial within a set period.
- Ability to follow the schedule. Volunteers need to be able to attend visits and complete the required procedures.
Eligibility Criteria in Mental Health Studies
Psychiatric studies apply the same principles with a few distinct features. One of the biggest is symptom severity. Because depression and anxiety are measured with clinician-rated scales, many studies require a score above a certain threshold. That means a person with a confirmed diagnosis but milder symptoms at the time of screening may not qualify, even though their condition is real and may still need treatment.
Co-occurring conditions also play a large role. Depression often appears alongside anxiety, substance use, or other conditions, and a study may exclude some of these combinations so it can measure the treatment’s effect on one condition at a time. Studies may also require that participants have not recently started or changed certain psychiatric medications.
Some exclusions exist specifically for safety. Studies commonly exclude people who are experiencing active thoughts of suicide or who need a higher level of care than a research setting provides. In those situations, the research team’s priority is connecting you with appropriate treatment right away.
Healthy Volunteer Studies
Not every study looks for people with a diagnosis. Some trials, especially early Phase 1 studies, enroll healthy volunteers to learn how a treatment is processed by the body and what doses are safe. Others use healthy volunteers as a comparison group. These studies have their own criteria, which often require normal lab results, no significant medical conditions, and no regular use of certain medications. For more on how the phases differ, see our overview of what a clinical study is.
How Eligibility Is Determined at LCCR
At the Lehigh Center for Clinical Research, eligibility is confirmed in stages. Most volunteers start with a short pre-screening questionnaire, completed online or by phone, that checks the basics. If a study looks like a possible fit, a member of our research team walks you through the informed consent form before any screening tests take place. A screening visit then confirms whether you meet the full criteria, using a review of your medical history, a clinical interview, and any exams or lab work the protocol requires.
Throughout the process, our team explains which criteria apply and why. For a detailed walkthrough of each step, from finding a study to your first visit, read our guide on how to sign up for clinical trials.
One request we make of every volunteer is complete honesty about your health history and medications. Criteria exist largely for your protection, and leaving something out could expose you to a risk the study team would otherwise have caught.
What Happens If You Don’t Qualify for a Clinical Trial?
Not qualifying is one of the most common outcomes of screening, and it is not a judgment about you. A 2003 study in the Journal of Clinical Psychiatry reviewed 186 people with major depression who applied to two antidepressant trials and found that only about 1 in 7 were enrolled. The most frequent reasons included bipolar disorder, substance use, symptoms that were too mild, a medical reason the drug would not be safe, and use of a medication the protocol did not allow.
Ask Why You Did Not Qualify
The study team can usually tell you the general reason you were not eligible. That information helps you understand whether a different study might be a better match, or whether your situation could change in a way that makes you eligible later.
Ask About Other Studies
Research sites often run several studies at once, each with different criteria. If you do not qualify for one LCCR study, ask our team whether another current study might fit, or whether we can contact you when new studies open.
Ask Whether Rescreening Is Possible
Some protocols allow a volunteer to screen again after a set period, for example after a medication change is complete or a lab value returns to the normal range. The study team can tell you whether the study you are interested in allows rescreening.
Follow Up on Any New Health Findings
Screening sometimes turns up something you did not know about, such as high blood pressure or an unusual lab result. If that happens, ask for a copy of the result and share it with your own doctor so it can be followed up as part of your regular care.
Keep Talking With Your Doctor
A clinical trial is one option among several. If a study is not the right fit right now, your doctor can help you review other treatments that may help while you wait for a study that matches your needs.
Frequently Asked Questions About Clinical Trial Eligibility
Can I join a clinical trial if I take other medications?
Often, yes. Many studies allow participants to keep taking medications for unrelated conditions. Some medications may be restricted because they could interact with the study treatment, and the study team will review your full list during screening.
Does not qualifying mean something is wrong with my health?
No. Most people who do not qualify are screened out because of study-specific requirements, such as symptom scores, medication history, or timing, rather than any new health problem. If screening does reveal a result that needs attention, the study team should let you know so you can follow up with your doctor.
Should I leave out information to improve my chances of qualifying?
No. Eligibility criteria are designed largely to protect you, and incomplete information could put you at risk from a treatment or procedure that is not safe for you. Being open with the study team helps them find the right study for you.
Do I have to live in Lehigh County to join a study at LCCR?
Studies generally do not require you to live in a particular county. You do need to be able to attend study visits in person on the protocol’s schedule, so consider travel time when you look at a study. Our team can explain the visit schedule for any study you are interested in.
Checking Your Eligibility for Studies at LCCR
The quickest way to find out whether you might qualify is to start with a specific study. Each listing includes the main requirements, and our research team can answer questions about the rest before you commit to anything.
View the clinical studies in the Lehigh Valley at the Lehigh Center for Clinical Research in Allentown, PA or contact our research team to talk through your eligibility. If you are still weighing whether research is right for you, our guide on why people participate in clinical trials covers the benefits and risks.
Medical disclaimer: This article is for general educational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk with a qualified healthcare provider about your individual health questions and before making any changes to your care. If you are in crisis or thinking about harming yourself, call or text 988 to reach the 988 Suicide & Crisis Lifeline.
Sources
- Zimmerman M, Mattia JI, Posternak MA. Are subjects in pharmacological treatment trials of depression representative of patients in routine clinical practice? American Journal of Psychiatry. 2002;159(3):469-473. doi:10.1176/appi.ajp.159.3.469.
- Keitner GI, Posternak MA, Ryan CE. How many subjects with major depressive disorder meet eligibility requirements of an antidepressant efficacy trial? Journal of Clinical Psychiatry. 2003;64(9):1091-1093. Full text.
