A clinical trial is defined as a study that observes or treats patients in order to develop or discover new treatments or medications. Virtually all medical advances happen because of the dedicated volunteers who have taken part in clinical trials; without them, the medical community couldn't go on to help thousands — even millions — of patients.

These carefully planned-out medical research studies allow scientists to answer questions like:”Does drug A work better than drug B?" or”Do patients recover faster if they get this new drug before or after cardiac surgery?" Scientists can accurately evaluate medications by studying the effects on healthy people and those with the condition the drug is designed to target.

Every new drug goes through rigorous preclinical laboratory testing on cells and animals. If and when — and only then — the drug shows potential as being safe and effective does it proceed to human clinical trials.

Each different trial follows a strict research plan — a protocol — established by researchers before the trial begins. This is the trial's blueprint, describing in detail:

  • The background;for example, what we know about the disease and the study drug so far
  • The rationale; for example, why we need to conduct this particular study and the question(s) we want to answer
  • The objective(s), for example, how we'll know if the drug works, and which measures we will use
  • The study design and methods, for example, what scientific rules the researchers will follow to test their hypotheses
  • The overall organization of the trial, for example, how often patients will be seen and the study team's various tasks
Above all, this kind of discipline ensures the safety of the participants through close contact and monitoring. It also ensures that results are accurate, well-documented, reliable and can be trusted.
We do clinical research to improve — or save — lives. Every advance in medical knowledge gets us closer to more effective treatments and relief for people suffering with a medical condition. In fact, science is all about constantly questioning and clinical trials are where so many of the answers are found.

The group that initiates a clinical trial is called a sponsor. This can be a company, a university or healthcare institution, a private or public group or even an individual.

The doctor who carries out the research itself and interacts with the patients is called the investigator or principal investigator. These highly qualified physicians typically have their own patients outside the trial setting. Doctors who dedicate their careers exclusively to clinical trials have the same medical training and qualifications as other physicians.

All trial doctors complete additional training on conducting clinical trials and research, and the particular understanding and attention paid to trial patients. 

Rest assured: who can conduct a clinical trial and under what conditions is highly regulated by governments.

International: Good Clinical Practice
National: UK Medicines & Healthcare products Regulatory Agency (MHRA)

Additional independent reviews and measures

Before and during a trial:

Ethics Committee

NHS National Institute for Health Research (NIHR)

Individual patient protection: Informed consent

This ensures that trials are as safe as possible, ethical and least likely to cause harm or affect a patient's well-being.

Good Clinical Practice protects patients.

The regulations applied in different countries are usually quite similar as they are based on the international standard called Good Clinical Practice and developed by the International Conference on Harmonisation (ICH).

The Medicines & Healthcare Products Regulatory Agency (MHRA) protects patients.

In the United Kingdom, clinical trials are regulated by the UK (MHRA). As the government agency responsible for national public health in the UK, the MHRA has a duty to make sure sponsors protect its participants' safety.

Informed consent protects patients.

Anyone who decides to take part in a clinical trial must give his or her consent before the trial begins. This ensures that patients fully understand the trial specifics and objectives and are kept informed as the trial progresses.

Informed consent is very important both for the patients and the researchers. Every participant should know all the details and how informed consent protects the clinical trial patient.


Each clinical trial has specific guidelines - its protocol -  dictate how the trial is to be run, including who may and may not participate.

Participation depends on the type of research, and often on the patients' safety. For example, a cardiac drug may affect someone with diabetes differently than other individuals, so people with diabetes are excluded. Sometimes the trial requires patients with a specific condition or a particular stage of a disease. Sometimes healthy volunteers are needed.

The reasons that allow you to volunteer for a trial are called inclusion criteria, and the reasons that disallow it are called exclusion criteria.

Find out whether participating in a clinical trial may be right for you.

Whether you want to join a clinical trial, or someone you love is considering it, or even if you're just curious, here we provide the essential information to fully understand the different trial phases and their objectives. We've also anticipated questions you may have and provided answers to questions that we often hear from clinical trial patients.    > Learn more

Clinical terms and language – how to read clinical trial information

The aim of a randomised trial is to divide patients into comparable groups — called arms. For example, by randomly assigning patients, each group can have:

  • People of similar age
  • A similar distribution of men and women
  • The same average disease severity

In randomised trials, the investigator also determines at random which treatment each patient receives — drug A or  drug B. At this stage, it isn't known which drug works better or even if, for example, drug 2 is the "newest."

In a blinded trial, patients do not know which medication they are receiving. This lets researchers compare the effects in the most impartial way possible.

Placebo-controlled trials compare results by giving the study drug to one group and a placebo (also called a sugar pill) to another group.

Find out more.

Government review agencies require that randomised, blinded , and placebo-controlled trials are done before a medication can be considered for marketing approval. This is to ensure drug effectiveness and impartial trial results. 

Find out more about Good Clinical Practice

What are Clinical Trial Phases?

Once the preclinical studies have shown that a drug may work and appears safe, it is tested on a very small group of healthy volunteers. There can be exceptions in phase 1 trials if they involve oncology or rare diseases where patients are very sick with no other alternatives.

Researchers' key questions:

  • How does the drug affect humans?
  • What is the safest dose?
  • What is the best way to take it (eg, by injection, pill, etc.)?
  • What are the drug's pharmacokinetics?
    •  How is it absorbed?
    • How is it distributed in the body (eg, does a pill reach all organs or stay in the stomach?)? (Important if we want to treat a liver disease and the drug does not get to the liver in good concentrations.)
    • How is it transformed by the body and eliminated?

At the end of phase 1, if the drug appears safe in healthy people, it proceeds to phase 2, where the drug is tested on a small number of people with the targeted disease. 

This will be the first time the drug is tested on patients with the disease targeted in the study. Researchers are looking for the efficacy and safety of the drug over a relatively short period of time, with 100 to 300 patients tested, often in   randomised , blinded , or placebo-controlled trials.

Researchers' key questions:

  • How effective is the drug on the targeted disease? 
  • What is its safety profile?
  • What dosage is the most effective with the fewest side effects?

Once phase 2 has tested efficacy, safety and optimal dosage with positive results, the drug can move on to phase 3 testing on more patients for a longer period.

The trial is now expanded to include many more patients with the targeted disease, tested over a longer period of time. This phase involves 300 to 3,000 patients, with tests designed to challenge the drug's longer-term effects. There is usually more than one phase 3 trial, since the drug is also compared to current medications or a placebo in randomised, blinded, or placebo-controlled trials.

Researchers' key questions:

  • How safe and effective is the drug over a longer term?
  • How does this drug compare to current medications for the same condition?
  • How does this drug compare to a placebo?

After phase 3 is completed successfully, the drug can be submitted for MHRA autherisation and eventual use by the general population. Once approved, the new medication can then be marketed. 

Also called post-marketing trials, phase 4 collects results after the medication has been introduced into the general population. These data complement all the results from the previous trial phases.

Sometimes, regulatory agencies like the MHRA autherise a medication for marketing only if the effects of the medication are further monitored in phase 4 trials, in slightly different patient groups than in phase 3, or for a longer period of time. Most often, these are observational studies that collect data from real-life patients taking the medication as prescribed by their doctors.

Researchers' key questions:

  • What are the new medication's long-term conditions for optimal use, efficacy and safety?
  • How does the new medication compare with others already on the market?
  • How does the medication affect the patients' quality of life?

Bringing a drug through all phases of research usually takes years, and isn't even possible without the collaboration of patients, doctors and study site staff. Every medication available has followed this long, rigorous path, closely monitored throughout by numerous levels of regulation.

Trial Methods in Detail

Many patients show a great deal of interest in the types of clinical trials, the different methodologies and why each one is used. Here, we go further into the subject, with more in-depth descriptions of the methods used — placebo-controlled, randomised or blinded — and the clear distinctions between them. 

What is a placebo?

A placebo is a treatment that contains no active medicinal ingredients. It will look and/or taste the same as the medication being studied, contain the same non-medicinal ingredients and be in the same form (e.g. pill, injection, etc.). For instance, a placebo can be a sugar pill or an injection of saline solution if the treatment is given by injection.

When is a placebo used or not used?

A placebo is often used in clinical trials to test how well a new drug works. If effective, the drug should produce better results than the placebo.

Comparing a new drug with a placebo can be the fastest and most reliable way to demonstrate the new drug's therapeutic effectiveness. However, assigning a patient to a placebo group can pose an ethical problem if it violates his or her right to receive the best available treatment. Placebos are never used if a patient would be put at risk by not having effective therapy — particularly in the case of serious illnesses, where most studies compare new drugs with an approved medication.

What is the placebo effect?

This is when a patient's symptoms improve after receiving a placebo. It seems to be due to the patient's strong belief or expectation that the treatment will work, along with the doctor's conviction that the treatment will work.

This is perfectly normal and does not mean that the patient's symptoms are not real. Scientists think the brain may produce substances that make the patient feel better and reduce his or her symptoms.

Will I know if placebos are going to be used in a trial?

Yes. You will be informed before participating in the clinical trial that you will either receive the medication being studied or a placebo, at random. It is unethical to not divulge this information.

What is an active-controlled trial?

Active-controlled trials compare a new drug to one that is already available — or compare approved medications to each other. There have been more of these recently than placebo-controlled studies because researchers can see how well a new drug works compared to a current standard-of-care medication. They are also always used when it would be unsafe or unethical to use a placebo on certain patients.

Is it better to be in the group getting the study drug?

Not necessarily. Until the clinical trial is completed and the trial findings are known, it isn't possible to know which of the two treatments is better. Regardless of the trial group you are in, the process ensures that you receive the same excellent medical care.

What is randomisation in trials?

In many trials, a patient is assigned to a specific study group. Randomisation is a process by which two different treatments or more are assigned by chance rather than by choice. This is done to avoid any bias while assigning patients to one group or another.

Why is randomisation used?

It is important to properly randomise patients between treatment groups that are being compared; randomisation ensures that any differences in results are due to the different treatments each group received and not other factors. 

What is blinding?

Blinding — or masking — is the process by which one or more parties involved with the trial do not know which patients have been assigned to which treatments. Types of blinding are explained below: single-blind, double-blind, triple-blind and no blinding (called open-label).

Why is blinding used?

The purpose of blinding is to prevent biases: if researchers knew which patient was getting the study treatment and which was getting the placebo, they might be tempted to give the (presumably helpful) study drug to a patient who could more easily benefit from it. A researcher might also give extra care to only the patients taking placebos to compensate for the placebo's ineffectiveness.

Not knowing which participants are receiving the active treatment allows the trial doctor and research staff to objectively observe patients during the study. Regardless of which treatment the patients get, however, the level of medical attention and care they receive is the same.

Similarly, a patient who does not know which treatment they are receiving cannot form an opinion about it that could unfairly influence the trial results.

What types of blinding can be used in trials?

Single-blind: The researchers are aware of the treatment they are administrating, but patients do not know which treatment they are receiving.

Double-blind: Two of the parties involved with the trial do not know which patients have been assigned to which treatments. Typically, this includes the researchers and the patients.

Triple-blind: Three of the parties involved do not know which patients have been assigned to which treatments. This often includes the researchers conducting the study, the patients and the researchers analysing the results collected.

Open-label: A trial in which blinding is not used. All parties involved know which patients have been assigned to which treatments. 

The Next Step – Joining a Clinical Trial

As we mention many times throughout this website, the decision to participate in a clinical trial is much appreciated and strictly voluntary. Once you feel strongly that you want to take part in a trial, there are many ways to find out about trials you might be eligible to join.

Your doctor may direct you to a trial you might be interested in and qualified to join. You may also have seen ads for trials in newspapers and on television, or heard them on the radio. Databases and websites are also good resources to see lists of clinical trials. Go to Find clinical trials to look through some of the studies conducted by AbbVie.

You can also browse trials at other reputable sources, including Clinicaltrials.gov, a website developed by the National Institutes of Health that provides current and unbiased information about clinical trials for a wide range of conditions.

The Ethics Committee evaluates and approve ads as part of thier review process.

Expect to find basic information in an ad for a clinical trial: the title and purpose of the study, main inclusion and exclusion criteria, the study site location(s) and how to contact the research site for more information.

It makes sense to discuss anything to do with your health with your doctor, including participation in a clinical trial. Doctors have their patients' best interests at heart and will let you know if there are any medical reasons why you should not participate.

We encourage you to do your own research as well to find trials in your region dedicated to your condition. Ask family and close friends to help in your learning and decision-making process. When they are included early on, they will be in a better position to provide support if you decide to join a trial. 

There can be significant differences among patients with the same disease — differences that require different treatments. And patients may have other health conditions that make their treatment more complex.

In a clinical trial, researchers need to be able to account for everything that might affect the study results. That is why, even if you have the medical condition, it may not be enough to be eligible.

Criteria for patient inclusion and exclusion are detailed in the study protocol and are generally listed in trial databases and briefly in ads. These criteria are in place to safeguard patients and ensure that the researchers glean the information they need from the trial. The trial's objectives will dictate the patients required: healthy or with specific illnesses or conditions.

Other inclusion and exclusion criteria may include:

  • Age
  • Gender
  • Stage or severity of a disease
  • Previous treatments a patient did or did not take
  • Medications a patient is currently taking
  • Medical conditions other than the one being studied
In order to qualify for a clinical trial, you must satisfy both the inclusion and exclusion criteria. Once you have contacted the research team, they will go through the informed consent process with you. When you have signed your consent form, you may undergo an additional screening process as outlined in the specific trial protocol.

What Happens When the Clinical Trial Is Over?

The end of the trial does not mark the end of all communication between you and the research team. Once treatment is completed and the study is closed, patients should feel free to ask the trial staff what treatment they were getting. The study staff share this information as soon as it is available and they are allowed to do so. They will also share the trial results when they become available.

If you request to see your data from the trial, researchers may have to wait until trial results are made public before sharing the information with you. Find out more.

After a clinical trial is completed, researchers carefully analyse all the data they collected. If findings are positive overall, or there is further analysis to do or more questions to answer, they may decide to move on to the next phase of testing. Or, they may decide to stop testing because the drug was not safe or effective enough.

When a phase 3 trial is completed, the researchers examine the data and decide if the study results warrant submission to government agencies for the medication's marketing approval.

Most clinical trials run for the planned length of time. Sometimes, though, the MHRA or the sponsor may end the trial early. The medication may be producing unexpected or more severe side effects — its harms outweighing its benefits. Another reason could be that not enough patients were recruited in the allotted time.

In some cases, a trial might be stopped because results are more positive than expected, for example, if there is clear evidence early on that the new drug is effective, the trial may be halted so that the new treatment can be made widely available as soon as possible. 


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All the information and answers you need before, during and after a clinical trial.