There is some evidence that long-term use of aspirin lowers the risk of developing non-cancerous growths (polyps) and bowel cancer. But aspirin may also cause side effects, such as indigestion or bleeding, and we don’t know how safe it is to take regularly. Doctors do not usually recommend taking aspirin regularly unless you’re taking part in a clinical trial. If you’re thinking of taking aspirin, speak to your GP or cancer specialist first. They can advise you on the safety of aspirin and whether it might benefit you.
How aspirin affects cancer risk
Some research studies show that people who take aspirin regularly for three years or more have a lower risk of getting cancer of the bowel, oesophagus (food pipe or gullet) and stomach. There is also some weaker evidence of reduced risk in breast, prostate and lung cancers.
Aspirin may also benefit people who have already been diagnosed with bowel cancer that has not spread to other parts of the body. A small number of studies have found that it reduces the risk of bowel cancer coming back after treatment but we need to more research to back this up.
Research shows that aspirin reduces the risk of bowel cancer in people who have Lynch syndrome. A clinical trial, called CaPP3, is comparing the effect of different doses of aspirin. The trial is recruiting people with Lynch syndrome to take part in the trial.
Aspirin may also benefit people with Lynch syndrome who are very overweight or obese. Some people with Lynch syndrome have an even higher risk of bowel cancer if they are very overweight. Aspirin may reduce this risk to match that of people with Lynch syndrome who are a healthy weight. The study involved small numbers of people who fit into this group so we need more research to find out more.
Side effects of aspirin
The most common side effects of aspirin are indigestion and bleeding. Up to one in every ten people (ten per cent) may get more nose bleeds, bleed for longer or bruise more easily.
In rare cases, aspirin can cause more serious side effects, like bleeding in the stomach. In some people, this risk may be outweighed by the benefit of reducing the risk of dying of cancer. Your GP can tell you if you are likely to benefit from regularly taking aspirin.
You may not be able to take aspirin if you have had other medical problems like asthma, stomach ulcers or problems with your liver, kidneys or heart. Your GP may check if you have bacteria called H pylori in your stomach, which can cause stomach ulcers. Getting rid of these bacteria can reduce the risk of stomach ulcers when you are taking aspirin.
Your doctor may not recommend you take aspirin if you have diabetes, drink heavily, smoke or are very overweight. This is because you may be at greater risk of bleeding in the stomach.
Speak to your specialist
We need more information about how aspirin works to lower the risk of bowel cancer, who it might help, what dose is best and how long people should take it for. Until we have these answers, doctors can’t recommend that people take aspirin regularly to prevent bowel cancer. If you’re thinking of taking aspirin, speak to your GP or cancer specialist first. They can advise you on the safety of aspirin and whether it might benefit you.
The following clinical trials are currently looking at the effects of aspirin on bowel cancer. Click on the links for more information about how to take part. If you’re interested in joining a trial, speak to your GP or cancer specialist. You might also like to read our information on taking part in a clinical trial.
This trial is looking at whether aspirin can help stop cancer coming back after treatment in people with early-stage cancer. It is recruiting new people to take part in the trial until the end of September 2021.
This trial is comparing different doses of aspirin, to see the effect on cancer risk in people with Lynch syndrome.
This study is looking at the effect of aspirin and a drug called ticagrelor on how cancer spreads. It is recruiting people with bowel cancer than has spread to another part of the body until 2 November 2019.
This trial is looking to see if aspirin helps radiotherapy to work better in people having radiotherapy before surgery for rectal cancer. Recruitment ends on 31 May 2016.
This trial is looking to see if a type of fish oil, on its own or together with aspirin, can stop small growths (polyps) in the bowel growing back after being removed. It finishes recruiting on 12 June 2016.
Updated March 2016. Due for review March 2018