Clinical Trials

Side effects and queries about clinical trials

Clinical trials are carefully designed to minimise the risks and maximise the benefits to everyone taking part, whatever treatment they receive. Some trials will involve very little risk. Researchers should explain to you what they already know about possible side effects to help you decide whether to take part. Clearly this will depend very much on the type of treatment being tested, so you will need to ask questions about the specific trial. Of course it can be worrying hearing about all the possible side effects, but it is important to bear in mind that not everyone reacts the same way.

In all trials the treatment may cause side effects or problems that doctors cannot predict. The risks may be greater when less is known about the treatment being tested, as in the Phase 1 trial for prostate cancer that Julian was involved in.
One of the main reasons for carrying out trials is so researchers can find out about side effects and measure how serious they are. If you take part you will be monitored carefully. You will have regular tests and may be asked questions about how you feel. (See also ‘Appointments, monitoring and questionnaires’). Many people mentioned the Phase 1 trial at a commercial research unit based at Northwick Park Hospital in 2006 when 6 healthy volunteers became extremely ill. A copy of the Inquiry Report of this incident can be downloaded from the National Archives (Expert Group on Phase One Clinical Trials: Final report).
Even though this was a different kind of trial to those experienced by the people we talked to, it had caused them to reflect on the balance of possible risks and benefits. However, most people felt they had been cared for very safely.
Iain Chalmers, one of the authors of the book 'Testing Treatments' (a web resource is available at, points out that side effects of treatment are a feature of medical care generally, and well-designed trials can in fact reduce unnecessary side effects for future patients.
It is important to report any side effects promptly, as this tells the researchers something important about treatments being tested. They may be able to help manage the side effects, or advise you whether you should stop taking part. Withdrawing from a trial because of side effects is entirely reasonable and no-one should feel they have to stay in for the sake of the trial or that they have failed if they stop. (See also ‘Thinking about withdrawing from a trial’).
Harry was able to stay in the trial with a change of medication, and others also said they were determined to keep going.
However, some people stopped, or took a break. Joanna’s husband was advised he could not continue in a trial of chemotherapy for leukaemia. She explained, “The treatment made him far too ill for them to be able to give him another treatment… Each time, when he was without immune resistance, his lung function got worse and worse and he got infected lungs. And by the time he had the last treatment…they said he couldn’t have another one. They wouldn’t risk it.”
Pam had serious side effects when taking part in an open-label expanded access study, and was advised to stop taking the drug for two weeks to give her a chance to recover from them.
While most people felt the researchers responded carefully and quickly to any worries about side effects, a few people felt they had not met with such a good response. Elizabeth decided not to take part in a trial of chemotherapy for ovarian cancer. (See ‘Deciding not to take part in a trial’).
Some people said they felt they were not being listened to, or that staff were not very interested in what they were reporting.
Leslie’s experience was particularly bad, and he remains very angry that his gastro-intestinal symptoms were not taken seriously for so long, even though the trial information sheet said there was a 1 in 10,000 risk of ulcers and bleeding in the gut.

Anyone taking part in a drug trial should also be told about other drugs or other substances, such as food or herbal remedies, which may interact with the trial drug and cause harmful side effects.
Sometimes trials which do not involve drugs can also involve side effects. Joanna took part in an ovarian cancer screening trial and found the internal scans were often uncomfortable, but it seemed to depend on the skill of the scanner. This seemed very important to her, so she was surprised this was information that the researchers did not collect. She was also made very anxious when she received an unexpected call to say she needed further tests. Again, she felt this was not well handled. The trial did include a questionnaire to measure people’s anxiety and emotional state, but Joanna felt the design of the questionnaire was flawed.
Merilyn was in a trial of different types of heart bypass surgery. She has since had a lot of pain, and has had psychological problems related to the size of her scar. She has a very good relationship with the research nurse, but she has found it difficult to get advice about the pain and whether it is related to the way the operation was done.

Last reviewed September 2018
Last updated September 2018


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