Participants in the Add-Aspirin trial take either aspirin or a placebo once a day for up to five years.
Find out more about the treatments used in Add-Aspirin here.

What is a placebo?

A placebo is a “dummy” tablet. It looks like an aspirin tablet but it doesn’t contain any medicine.
We are using a placebo in this study so that we can make as clear an assessment as possible about the effects of aspirin. To make sure the results are as reliable as possible, neither the participants, nor the doctors, will know or be able to choose who is taking aspirin and who is taking a placebo.

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Run-in treatment

Aspirin is a common, frequently used drug and most people take it without experiencing any side effects. However, a key aspect of any clinical trial is protecting the safety of the participants.
In order to help us identify people for whom regular aspirin use may not be suitable, all Add-Aspirin participants are asked to take a 100mg aspirin tablet once a day for about eight weeks at the beginning of the study. This phase of the study is called the run-in.
Participants who do not want to carry on taking tablets every day or who experience side effects may be advised not to continue taking part.

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Study treatment

Participants who continue to take part in the study after the run-in are randomly assigned by a computer to take either aspirin or a placebo, which they will take once a day for up to five years.
All participants have a two out of three chance of receiving aspirin. Some participants receive 300mg aspirin whilst others receive 100mg. Using different doses allows us to investigate how much aspirin may be needed to have an effect, if any, against cancer.
To make the assessment of aspirin as reliable as possible, in this phase of the study neither participants nor their doctors know which treatment they are taking.
However, all NHS doctors can find out which treatment a participant is taking if they need to in a medical emergency. This is known as unblinding.

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Taking the treatment

Add-Aspirin participants take one tablet once a day, every day for up to five years. Tablets should be swallowed whole with plenty of water, preferably after a meal.
It is very important that the tablets are taken every day. It is usually easier to remember to do this if the tablet is taken at the same time each day. If you forget to take a tablet, do not take additional tablets to catch up, you should only take one tablet a day.

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Other medications

It is extremely important that Add-Aspirin trial participants do not take other medications that contain aspirin regularly whilst they are taking part in the study. It is also important that participants do not take aspirin bought from a chemist or shop. This may be unsafe and could also interfere with the results of the study.
In many cases, alternative medications that do not contain aspirin are available. Your study doctor or GP will be able to advise on this. Click here for more information on what medications to avoid.   

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The trial is being jointly funded by Cancer Research UK (grant number C471 /A15015,, the National Institute for Health Research Health Technology Assessment Programme (project number 12/01/38, and the MRC Clinical Trials Unit at UCL.
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