Is taking part in a clinical trial safe? A patient's guide

What makes a clinical trial safe to take part in?

A clinical trial is considered safe to run when its risks to participants have been assessed and minimised before recruitment starts, and when an independent ethics committee has confirmed that the potential benefits justify those risks. This does not mean the treatment being tested is risk-free – it means the uncertainty around it has been reduced as much as possible before you are exposed to it. Trust in this process matters because it is what allows patients and healthy volunteers to make a genuinely informed decision, rather than a leap of faith, about whether to join a study^[1].

Before any trial involving people begins, the treatment goes through preclinical studies – laboratory tests and, where relevant, animal studies – designed to catch major safety problems early^[2]. Only treatments that clear this stage move on to being tested in people^[3]. National medicines authorities also play a role in overseeing clinical trials, working to ensure that the balance between benefits and risks to patients remains positive^[2].

A common myth is that trials are inherently dangerous and that participants have little protection. In fact, every trial is planned and monitored specifically to minimise risk to participants, and a trial plan will not be approved if the potential risk to participants is judged too great^[4].

Who reviews and approves a clinical trial before it can start?

A clinical trial cannot recruit participants until it has received a positive opinion from an ethics committee and approval from the relevant national authority^[5]. In the UK, for example, the Health Research Authority co-ordinates 64 Research Ethics Committees, and no trial can go ahead without their approval^[1].

These committees ask a specific set of questions before signing off on a trial: is this research in the best interests of patients, is it safe, and what are the risks to participants. Committee members include both healthcare professionals and people who have previously taken part in trials as participants themselves^[1].

Trials must also follow Good Clinical Practice (GCP) and the ethical principles of the Declaration of Helsinki^[5]. Detailed documentation for every trial is reviewed by multiple experts specifically to ensure it is as safe as possible^[4].

For comparison, in the United States, clinical trials require approval from the FDA before they can start, alongside review by an institutional review board (IRB) at each participating hospital, which focuses on participant safety and rights^[3].

What does informed consent actually protect you against?

Informed consent is the conversation and document through which the research team explains the trial's goals, procedures, known risks, potential benefits, and any alternatives to taking part. It also states clearly how long the trial may last, what follow-up is required, and any costs or compensation involved^[3].

If the document is hard to follow because of medical or legal language, you can always ask the researcher or research team for clarification before signing anything. Making sure you fully understand and are comfortable with your decision is treated as essential to the whole research process, not a formality, and no one should feel rushed into signing before every question has been answered to their satisfaction^[4].

The consent document will also state whether the trial is randomised – meaning that, like a coin flip, not everyone will receive the experimental treatment. This is important to know if you are hoping specifically to receive the new treatment rather than a standard one^[3].

Who is eligible to take part in a clinical trial?

Each clinical trial has its own inclusion and exclusion criteria that determine who can and cannot take part – for example, requirements around age, sex or a specific health condition. These criteria exist specifically to keep the trial as safe as possible for everyone involved, since including someone for whom the treatment is likely to be unsuitable would raise their personal risk without adding anything useful to the study's findings^[4].

Potential volunteers are carefully screened against these requirements before being accepted, and most exclusions are related to safety concerns. Both people with a diagnosed medical condition and healthy volunteers can take part, and participation is always completely voluntary^[6].

Trials also exist for children specifically, since paediatric trials are needed to adjust treatments to children's particular needs. Clinical trials also are not limited to people with serious illness – some focus on improving quality of life, preventing disease, or diagnosing it earlier, which means the population being studied and the level of acceptable risk can look quite different from one trial to the next^[4].

How does the level of risk change across trial phases?

Risk in a clinical trial is not the same at every stage – it is generally highest in the earliest phase and decreases as more is learned about a treatment. Even in phase 1 or phase 2 trials, treatments have already been carefully researched in the laboratory before being given to people, so no one steps into a first-in-human study with nothing more than a theoretical idea behind it^[7].

Phase	What is tested	Typical participants	Risk profile
Phase 1	Safety, side effects, and dose-finding for a medicine given to people for the first time	Small number of people, who may be healthy volunteers	Highest uncertainty; researchers start with small doses and only raise them if side effects are absent or minor[8]
Phase 2	Short-term effects of the new medicine	Larger group of people who are ill	More is known than in phase 1, but effectiveness and side effects are still being established[8]
Phase 3	Comparison against an existing treatment or placebo, including important side effects	Several thousand patients; often lasts a year or more	Lower risk of harmful side effects, since doctors know more about the treatment by this stage[7]
Phase 4	Ongoing safety, side effects and effectiveness after marketing authorisation	People using the medicine on prescription in routine practice	Treatment already authorised; conducted as needed, not for every medicine[8][5],

What are control groups, randomisation and blinding, and why do they matter for safety?

If you take part in a trial, you are usually randomly assigned either to a treatment group, which receives the treatment being assessed, or to a control group, which receives an existing standard treatment or a placebo if no proven standard treatment exists. Researchers try to keep every other condition as similar as possible between the two groups so that any difference observed can be attributed to the treatment itself^[8].

This design does not increase your personal medical risk beyond what has already been assessed by the ethics committee – it is a method for producing a reliable answer about whether the treatment works, not a way of exposing you to an unapproved intervention. Understanding this distinction can help ease a common worry, which is the fear of somehow being given something untested and unsupervised simply because the study is randomised^[8].

What are the pros and cons of taking part in a clinical trial?

Weighing up a trial means looking honestly at both what you might gain and what it might cost you in time, discomfort or risk^[7].

• You may access a treatment that is only available through a trial, and it may work better than the standard treatment. No one can know this for certain in advance, which is the reason the trial is being run^[7].
• You are likely to have more blood tests, scans or other check-ups. For some people this extra monitoring feels reassuring, while for others it increases anxiety about their condition^[7].
• You may experience unexpected or serious side effects, and there is some risk that an experimental treatment could harm you. The research team will tell you what is known about likely side effects before you decide^[7].
• There may be practical costs – extra travel, parking or time off – though some trial teams reimburse participants for these expenses^[7][8].,
• Taking part may involve restrictions during the trial period, such as being asked not to eat or not to drink alcohol for a set time, and some trials require an overnight stay^[8].
• Your participation contributes to medical knowledge that may help other patients with the same condition in the future, regardless of whether the treatment turns out to work for you personally^[8].

None of these points is meant to make the decision for you; rather, they are the kind of trade-offs the research team should walk through with you individually, since what counts as a manageable inconvenience for one person may be a genuine barrier for another^[7].

Will taking part in a clinical trial cost you money, or will you be paid?

Participation in a clinical trial is usually free of charge. Depending on the specific trial and its location, there may be additional costs such as travel, parking or accommodation, and many trials offer to reimburse participants for these expenses^[4].

Some trials offer payment that varies depending on what is expected of you, while others cover only travel expenses without additional payment. Find out about the inconvenience and time commitment involved before you sign up, and weigh carefully whether it is worth it for you personally, since a trial that suits someone with a flexible schedule and nearby transport may be far more demanding for someone without those advantages^[8].

What rights do you keep once you have joined a trial?

Every participant in a clinical trial has the right to withdraw at any time, without giving a reason and without any consequences for their future care^[4][3].,

You also keep the right to ask your doctor about your condition and to see your own medical records at any point during the trial^[4]. An informed consent document is not a binding contract that removes these rights – it records what you have been told and what you have agreed to, not an obligation to see the trial through, and it can never be used to pressure someone into staying in a study they no longer wish to be part of^[3].

Participants also have the right to be told about the trial's purpose, potential benefits and risks, and to receive a full informed consent form covering these details before agreeing to take part^[4].

When should you speak to your doctor or the research team before or during a trial?

Speak to your doctor or the trial's research team before joining if you do not fully understand the informed consent document – you are entitled to ask for clarification of any medical or legal language it contains, and a well-run trial team will expect and welcome these questions rather than treat them as an obstacle to recruitment^[4].

Your own doctor may not know about every trial you could be eligible for, so it is worth asking directly, and also checking patient organisations, charities and trial registers relevant to your condition^[4][8].,

Once enrolled, contact the research team if you experience a side effect, if your health changes, or if you are unsure whether a symptom is related to the trial treatment – this is part of the ongoing monitoring that doctors carry out throughout the trial, and reporting anything unusual promptly helps them keep the study safe not just for you but for everyone else taking part^[4].

If you wish to stop taking part at any stage, tell the research team directly – withdrawal is your right and carries no consequences for your ongoing care^[4].

Summary

Clinical trials are not risk-free, but the risk you take on is reviewed, documented and limited before you are ever asked to consent. Ethics committee approval, national authority sign-off, preclinical testing, eligibility criteria and the informed consent process all exist specifically to keep that risk as low as reasonably possible while still answering a genuine medical question.

Deciding whether to take part is a personal balance between potential benefit, extra monitoring, possible side effects, and the practical cost in time and travel. You keep the right to ask questions before signing, to see your own medical information throughout, and to withdraw at any point without consequence – those rights do not expire once you have agreed to join.

This article is for general information and does not replace individual medical advice. Speak to your doctor or the trial's research team about your specific situation before deciding to take part in a clinical trial.

1. [1] The importance of trust in clinical trial safety - Health Research Authority (accessed 2 June 2026) – https://www.hra.nhs.uk/about-us/news-updates/importance-trust-clinical-trial-safety/
2. [2] Overseeing clinical trials - ANSM (accessed 2 June 2026) – https://ansm.sante.fr/qui-sommes-nous/our-missions/facilitating-access-to-therapeutic-innovation/p/overseeing-clinical-trials
3. [3] What Is a Clinical Trial? - Cleveland Clinic (accessed 2 June 2026) – https://my.clevelandclinic.org/health/articles/clinical-trial
4. [4] Myths & Facts About Clinical Trials - Agencja Badań Medycznych (ABM) (accessed 2 June 2026) – https://abm.gov.pl/download/1/9052/Brochure-Mythsandfactsaboutclinicaltrails.pdf
5. [5] Clinical Trials - Paul-Ehrlich-Institut (accessed 2 June 2026) – https://www.pei.de/EN/regulation/clinical-trials/clinical-trials-content.html
6. [6] Clinical Research: What Is It? - Johns Hopkins Medicine (accessed 2 June 2026) – https://www.hopkinsmedicine.org/research/understanding-clinical-trials/clinical-research-what-is-it
7. [7] The pros and cons of taking part in a clinical trial - Cancer Research UK (accessed 2 June 2026) – https://www.cancerresearchuk.org/about-cancer/find-a-clinical-trial/what-you-should-be-told-about-a-clinical-trial/advantages-and-drawbacks
8. [8] Clinical trials (Be Part of Research and related registers) - NHS (accessed 2 June 2026) – https://www.nhs.uk/tests-and-treatments/clinical-trials/