What to realistically expect from participating in a clinical trial.
Be realistic. This is experimental treatment. Unknown side effects are possible. Some participants experience serious adverse events. Some trials are stopped early because the treatment is harmful. This is rare, but it happens.
You are also making a time commitment. Visits might be frequent. Travel might be required. You might miss work. There are indirect costs around time, energy, and emotional labor. Some trials require long-term follow-up for years after the main study ends. FDA guidance recommends up to 15 years of follow-up for gene therapies that integrate into DNA or edit genes, and up to 5 years for AAV-based gene therapies.
There is no guarantee it will work for you. Even if a treatment works for the majority of participants, it might not work for you. You might be enrolled, complete all the visits, follow all the protocol requirements, and see no benefit. In randomized trials, you may receive placebo and not the active drug at all.
The risk profile of a trial drug varies dramatically by phase, and understanding which phase you are entering helps frame realistic expectations.
Phase 1 trials are the first time a drug is given to humans (or to humans with the target condition, depending on the design). Side effects are often unknown, and dose-finding is the primary purpose. FDA estimates that about 70% of drugs move from Phase 1 to Phase 2. Drugs stop for many reasons, including safety problems, weak early results and business decisions. Volunteers in Phase 1 trials are typically monitored intensively.
Phase 2 trials have early efficacy data but limited safety information. Common side effects from Phase 1 are usually known, but rare or delayed side effects may not yet be apparent. About 33% of Phase 2 drugs advance to Phase 3 in most therapeutic areas. The most common reasons for Phase 2 failure are lack of efficacy and unexpected safety findings.
Phase 3 trials have a more complete safety profile. The drug has been given to hundreds of patients, and the reasonably foreseeable risks and side effects must be described in the informed consent form. Rare side effects (occurring in less than 1 in 1000 patients) may still emerge in larger Phase 3 populations or after approval.
Phase 4 trials happen after FDA approval and capture long-term safety, rare side effects, and real-world effectiveness. By Phase 4, the most common side effects are well-characterized in the FDA-approved label. Ask your trial coordinator whether the consent form has been updated with any new safety findings since the trial began. Researchers must tell you about significant new findings that might affect your willingness to stay in the trial.
A serious adverse event (SAE) is any medical event that meets one of several regulatory criteria. The criteria include outcomes that result in death, are life-threatening, require inpatient hospitalization or prolong an existing hospitalization, cause persistent or significant disability or incapacity, cause a congenital anomaly, or are medically important conditions that may jeopardize the patient and require intervention to prevent the other outcomes.
When an SAE occurs, federal rules require the trial investigator to report it to the sponsor immediately, and most protocols set a 24-hour deadline. The sponsor must report serious, unexpected suspected drug reactions to the FDA within 15 calendar days, or within 7 calendar days if the reaction was fatal or life-threatening. The Data Safety Monitoring Board (DSMB), if one exists for the trial, reviews accumulated SAE data and can recommend stopping the trial or modifying the protocol.
If you experience an SAE, you should immediately receive medical care for the event itself. U.S. law does not require sponsors to pay for trial-related injuries. For trials with more than minimal risk, the consent form must explain whether any compensation or medical treatment is available if you are injured. The informed consent form should describe what happens if you are injured. If it does not, ask before signing.
Rare disease patients face risk considerations that do not apply to common-condition trials. The candidate pool is small, so trial sites often have limited prior experience with the specific disease. The disease itself may be progressing, and trial visits may compete with urgent clinical management. Standard-of-care benchmarks may be poorly defined, which makes it harder to know whether you are doing better, worse, or the same as you would without the trial.
Travel risk is real for rare disease trials. Most rare disease trials are concentrated at a small number of expert centers, and weekly or monthly travel for years can be its own health burden, especially for patients with mobility limitations or autonomic dysfunction. Decentralized clinical trials have made some visits virtual, but not all assessments can be done remotely.
Drug-drug interactions and disease-specific physiology can produce side effects in rare disease populations that did not appear in healthy volunteers or in trials of more common conditions. For rare metabolic, mitochondrial, or autonomic conditions specifically, anesthesia, gadolinium-based contrast, fasting requirements, and certain blood-draw schedules may carry risks that the trial coordinator (if newer to the disease) may not fully anticipate. Ask your specialist to review the protocol before you sign.
Only about 5% of rare diseases have an FDA-approved treatment. For many patients, a clinical trial is the only way to try a therapy aimed at the disease itself rather than its symptoms.
You get access to cutting-edge medicine years before it might be available through normal channels. You are not waiting for FDA approval. You are trying something new. For sickle cell disease, for example, participants in the Casgevy trials received the therapy several years before FDA approved it in December 2023.
You also get close medical monitoring. Blood work is frequent. Researchers are watching for problems. If something is wrong, they catch it early. For some people with rare diseases, a clinical trial provides better medical care than they would get outside the trial because they are being monitored so carefully and seen by specialists who focus on the condition.
There is meaning, too. You are contributing to scientific understanding of your disease. You are helping the thousands of people who will come after you. For many patients, that is a significant benefit in itself, separate from any direct medical benefit of the drug.
The direct medical benefit of the drug is the most discussed reason to enroll, but the practical, ancillary benefits matter too and often surprise first-time participants.
Diagnostic confirmation. Many rare disease trials require confirmatory genetic testing, biomarker panels, or specialty imaging that you would not otherwise get. Patients sometimes learn for the first time during trial screening which exact mutation they carry, which informs family planning and connects them with the right disease subtype community.
Specialist access. Rare disease trials are usually run by physicians who are world experts in the condition. Even if the drug fails, you have established a relationship with a specialist who can guide you through future treatment decisions, including off-label medications, the next trial, or expanded access programs.
Patient community. Trial sites often connect participants with each other, formally through patient advisory boards or informally through waiting-room introductions. For rare diseases where patients rarely meet in person, this is one of the few in-person community-building experiences available.
Detailed health data. Trial protocols generate dense, longitudinal health data (lab values, imaging, functional assessments) that you can ask about. Some trials can hold back your research records until the study ends if you agreed to that when you signed consent, so ask what you will receive and when. For rare disease patients, this kind of structured longitudinal data is hard to assemble outside of a trial and can inform care for years after participation ends.
Most investigational drugs do not become approved medicines. Across all therapeutic areas, fewer than 10% of drugs that enter Phase 1 testing eventually receive FDA approval, with the highest attrition occurring in Phase 2 (lack of efficacy) and Phase 3 (failure to beat the comparator or unexpected safety findings). Even drugs that ultimately succeed have many participants in early-phase studies who saw no benefit because the dose was too low, the patient population was wrong, or the drug failed to engage its target.
If the drug does not work for you, the trial team should help you transition back to standard care. This often includes a structured taper schedule, follow-up safety visits to monitor for delayed adverse events, and an honest conversation about other trials or off-label options. You keep access to standard medical care, and you can ask the team which of your trial results you will receive and when.
Emotionally, a trial that does not work is hard. Patients often invest months of hope and travel, and a negative result can feel like a personal failure even though it is not. Your disease's patient organization can often connect you with support groups and help you look for the next trial.
This is deeply personal. For someone with a rare disease and no other treatment options, the risk-benefit calculation might look very different than for someone with established treatments available. There is no right answer. The right answer is what makes sense for you, your health, your life, and your values.
A practical risk-benefit framework for trial decision-making considers the severity and trajectory of your disease without intervention, the strength of preclinical and prior-trial evidence for the drug, the realistic probability of being assigned to placebo, the time and travel commitment required, post-trial drug access pathways, and your own tolerance for uncertainty. None of these can be optimized in isolation.
Discuss it with your doctors, your family, your advocate organization. Get honest information about the risks from the trial coordinators. Ask about side effects, complications, what happens if something goes wrong. You deserve to understand what you are signing up for. The list of 15 questions on our questions-to-ask page is a useful starting point.
The main risks of participating in a clinical trial include unknown side effects from an investigational drug, the possibility of receiving placebo instead of the active treatment, time and travel commitments, indirect costs (lost wages, child care, fuel), and the possibility that the drug does not work for you. Serious adverse events occur in a minority of participants but are possible, and some trials are stopped early due to safety concerns.
The main benefits of joining a clinical trial include access to investigational treatments years before commercial approval, close medical monitoring by specialists, detailed health data about your condition, a meaningful contribution to scientific understanding of your disease, and (for many rare diseases) access to the only treatment option available. Some trials reimburse travel, lodging, and meals, which makes specialist care more accessible than it would otherwise be.
A serious adverse event (SAE) in a clinical trial is any medical event that results in death, is life-threatening, requires inpatient hospitalization or prolongs hospitalization, causes persistent or significant disability, causes a congenital anomaly, or is a medically important condition that may require intervention to prevent these outcomes. Trial investigators must report SAEs to the sponsor immediately (most protocols say within 24 hours). Sponsors must report serious, unexpected suspected drug reactions to the FDA within 15 calendar days, or within 7 days if fatal or life-threatening.
Phase 1 clinical trials carry the highest uncertainty about side effects because the drug has not been given to many humans before. Phase 1 trials are tightly regulated, monitored intensively, and typically conducted at experienced centers with rapid intervention capacity. FDA estimates that about 70% of drugs move from Phase 1 to Phase 2. Drugs that stop do so for many reasons, including safety, weak early results and business decisions. For patients with serious or life-threatening rare diseases without other options, Phase 1 trial participation is often a reasonable choice; for patients with milder forms of disease and existing treatment options, the risk-benefit calculation may not justify Phase 1 participation.
Whether you receive placebo or the active drug depends on the trial design. Many rare disease trials use weighted randomization (more participants on active drug than placebo), open-label designs (everyone receives the active drug), or crossover designs (everyone receives both at different time points). Many pivotal Phase 3 trials include an open-label extension where placebo participants can switch to the active drug after the blinded portion ends. Ask the trial coordinator for the randomization ratio and whether an open-label extension is part of the protocol.
The sponsor of a clinical trial typically pays for medical care directly related to a trial-caused injury, but the specific terms vary by sponsor, country, and trial. For trials with more than minimal risk, the informed consent form must explain whether compensation or medical treatment is available if you are injured. Federal law does not require sponsors to provide compensation for injury in U.S. trials. Ask the trial coordinator whether the sponsor carries clinical trial liability insurance and whether compensation for lost wages or long-term disability is part of the agreement.
Across all therapeutic areas, fewer than 10% of drugs that enter Phase 1 clinical trials eventually receive FDA approval. Approval rates vary by disease area. In BIO's 2011 to 2020 analysis, hematology drugs had the highest success rate and cancer drugs among the lowest, and rare disease drugs did better than average.
Yes, a clinical trial can be stopped early for several reasons. The Data Safety Monitoring Board (DSMB) can recommend stopping for safety (the drug is causing serious harm) or for efficacy (the drug is working so well that it would be unethical to continue placebo). The sponsor can stop a trial for business reasons (manufacturing problems, strategic redirection). The FDA can halt a trial through a clinical hold. Patients are notified when a trial is stopped, and the team must explain the reason and the next steps for ongoing safety follow-up.