Risks of Clinical Trials
An honest look at what could go wrong, what protections exist, and how to make an informed decision about participation.
GuineaPig Editorial Team
Medical Research Experts
Clinical trials offer compensation and the opportunity to contribute to medical research, but they also involve real risks. Before enrolling in any study, it is essential to understand what could go wrong, what protections exist, and how to make an informed decision. This guide covers the potential risks of clinical trial participation, with a focus on Phase 1 studies where healthy volunteers are most commonly recruited.
No one should pressure you to participate in a clinical trial, and no amount of compensation is worth taking on risks you do not fully understand. Read this guide, read your informed consent document carefully, and ask questions until you are comfortable with your decision.
“No amount of compensation is worth taking on risks you do not fully understand.
What Are the Risks of Clinical Trials?
Clinical trials test treatments that are not yet fully proven. By definition, there is uncertainty about how a study drug will affect participants. Here are the main categories of risk:
Unknown Side Effects
In Phase 1 studies, the drug has typically only been tested in animals and perhaps a small number of humans before you. While preclinical testing provides important safety data, it cannot predict every reaction in humans. Side effects may emerge during the trial that were not anticipated. These could be mild and temporary, or in rare cases, serious and lasting.
The Reality of Early-Phase Trials
When you participate in a Phase 1 study, you are among the first humans to receive this compound. The safety profile is based largely on animal studies, which do not always predict human responses accurately.
Common Side Effects in Phase 1 Studies
The most frequently reported side effects in healthy volunteer studies tend to be mild and resolve on their own:
- Headache
- Nausea or upset stomach
- Fatigue or drowsiness
- Dizziness
- Injection site reactions (redness, soreness, swelling)
- Changes in appetite
- Mild skin reactions
However, the specific risks depend entirely on the drug being tested. The informed consent document for each study will list the known and anticipated risks based on preclinical data.
Serious Adverse Events
Serious adverse events (SAEs) are rare but do occur. These are events that result in hospitalization, disability, birth defects, or death. The FDA maintains strict reporting requirements for SAEs, and any serious safety signal can result in a study being paused or terminated.
A Sobering Example
In 2016, a Phase 1 trial in France resulted in one death and several participants hospitalized with neurological damage. Such events are exceptional, but they underscore that risks are real.
Long-Term Effects
Some side effects may not appear immediately. Long-term effects of a new drug may take months or years to manifest, and by the time they do, the study will have ended. This is an inherent limitation of early-phase trials — the long-term safety profile of a new drug is simply not known yet.
If you participate in a Phase 1 study, you are accepting some level of uncertainty about effects that may emerge later.
Discomfort and Inconvenience
Beyond drug-related risks, clinical trials can be physically uncomfortable. Phase 1 studies often involve:
- Numerous blood draws (sometimes 10-20 per day during intensive sampling)
- Restricted diet and no outside food
- Limited mobility and confinement to the clinic
- Disrupted sleep schedules for overnight blood draws
- Boredom during extended inpatient stays
These inconveniences are part of the reason healthy volunteer studies pay well — you are being compensated for your time, discomfort, and the restrictions placed on your daily life.
Risk Assessment by Study Type
Post-market studies with approved drugs. Lowest uncertainty.
Well-understood mechanisms, established safety profiles.
Some human data available, but still being evaluated.
First-in-human testing. Limited human safety data.
New drug classes or mechanisms. Highest uncertainty.
Risk levels are relative and depend on individual health factors. Always consult with the research team.
Your Rights as a Participant
Clinical trial participants have significant legal protections. Understanding your rights is essential to making an informed decision and protecting yourself throughout the study.
Key Rights to Remember
Informed consent: You must receive complete information about the study before deciding to participate.
Right to withdraw: You can leave any time, for any reason, without penalty.
Medical care: If injured due to the study, you are entitled to treatment at no cost.
Privacy: Your health information is protected under HIPAA.
IRB oversight: An independent ethics committee monitors the study.
Questions to Ask Before Enrolling
Before signing the informed consent, ask the study coordinator or physician these questions:
- What are the known risks of this specific drug? Ask about what was seen in animal studies and any prior human testing.
- What side effects have other participants experienced? If this is not the first cohort, ask what has been observed so far.
- What happens if I have a bad reaction? Understand the emergency protocols and what medical care is available on-site.
- Who pays for medical treatment if I am injured? Clarify what is covered and what limitations exist.
- Can I leave at any time without penalty? Confirm your right to withdraw and understand the payment implications.
- What is the time commitment? Understand the full schedule, including follow-up visits and washout periods.
- What restrictions will I have during the study? Ask about diet, alcohol, caffeine, medications, and physical activity.
- Who can I contact with concerns? Get contact information for the principal investigator and the IRB.
How to Protect Yourself
While clinical trials have safety oversight, you are your own best advocate. Here is how to protect yourself:
- Read the entire informed consent document. Do not skim it. Understand every section, especially the risks and the compensation for injury clause.
- Ask questions until you understand. If something is unclear, ask for clarification. There are no dumb questions when it comes to your safety.
- Be honest about your medical history. Screening exists to protect you. Hiding information can put your health at risk.
- Report any symptoms immediately. During the study, tell the research staff about any side effects, no matter how minor they seem.
- Know your exit. Remember that you can leave at any time. If you feel unsafe or uncomfortable, withdraw.
- Keep your own records. Document your experience, including any symptoms, medications received, and communications with the research team.
FDA Resources on Participant Safety
The U.S. Food and Drug Administration provides extensive resources for clinical trial participants:
- Clinical Trials: What Patients Need to Know — FDA overview of clinical trial participation
- Informed Consent for Clinical Trials — FDA guidance on the informed consent process
- Clinical Trials and Human Subject Protection — FDA regulations protecting research participants
- ClinicalTrials.gov — NIH database of clinical studies
Frequently Asked Questions
Frequently Asked Questions
Clinical trials have significant safety oversight, including FDA regulation, IRB approval, and continuous monitoring. The overall safety record is good, and serious adverse events are rare. However, no trial is risk-free. You are testing something that is not yet fully proven, and there is always some uncertainty about how it will affect you.
Continue Reading
Ready to explore clinical trials with informed eyes?
Browse thousands of opportunities and make educated decisions about participation.
Browse Clinical Trials