NOTE: This post is from 2012. For discussion of today’s headlines please read this post.

An old bottle of aspirin

Aspirin has been around for over a century

“Should I be taking aspirin to reduce the risk of dying from cancer?”

This is likely to be the question on many people’s minds today, which sees the publication of three reports on the effects of aspirin on cancer risk, and cancer spread – two in the Lancet, and one in sister journal Lancet Oncology.

But before we look at today’s studies, we need to set the scene. Over the last few years, the evidence has been building that regularly taking the simple, cheap drug aspirin could reduce the risk of dying from cancer.

For example, a large study from December 2010 showed that people who took 75 milligrams of aspirin (the same dose as in a ‘junior’ aspirin) every day had a reduced risk ofdying from cancer.

But these results didn’t answer all the questions, and we felt it was too early to start recommending that people take low-dose aspirin every day. This is because aspirin’s not a harmless drug. In some people it can cause serious side effects, like internal bleeding.

On top of this, it wasn’t clear what the best dose is, or at what age it’s best to start taking aspirin.

Today’s studies clarify the picture a little, but because of the uncertainties we’re still recommending that people discuss things with their doctor before taking aspirin.

Here’s our Chief Medical Officer, Professor Peter Johnson, on the subject:

What do the latest studies add?

The three studies published today were all led by Professor Peter Rothwell at Oxford University, who’s one of the world’s top aspirin researchers.

The studies looked at data from several large trials of taking daily, low-dose aspirin that aimed to find out aspirin’s effect on heart disease, and also measured how many people were diagnosed with cancer.

Preventing cancer

Taken together, the studies provided more information about how aspirin affects the risk of cancer developing in the first place.

Earlier studies had shown that aspirin probably reduces the risk of developing bowel cancer, and some other cancers in the digestive system. But this study showed that, after three years of daily low-dose aspirin, the risk of developing cancer at all dropped significantly in both men and women.

In fact, there were nine cases of cancer in every 1,000 people taking aspirin, compared with twelve cases per 1,000 people not taking it – an absolute reduction of three cases per 1,000 people.

The cancers most strongly prevented were oesophageal, stomach, bowel and lung cancers.

Preventing cancer spreading

But a new – and somewhat unexpected – finding from this research is that cancer patients taking aspirin every day appeared to have a reduced risk of their cancers spreading.

In fact, not only were regular aspirin-takers less likely to be diagnosed with a cancer that’d already spread, but (compared to non-aspirin takers) patients on aspirin diagnosed with early localised cancers had a lower chance that their cancer would spread later on.

This is important, because when a cancer spreads it is much more difficult to treat, and nine out of ten cancer deaths are due to the disease spreading.

And it also hints that aspirin could be useful for people who’ve already been diagnosed with cancer – though, importantly, this will depend on the individual case.

This is because some cancer patients will also have a higher than normal risk of bleeding, because of their cancer or treatment. So it’s important that people with cancer talk to their doctors rather than deciding to take aspirin by themselves.

Because of these two effects (the reduced risk of getting cancer, and the prevention of it spreading) , the research also suggested that regularly taking aspirin reduced the risk of dying from cancer by nearly 40 per cent after people had been taking it for 5 years.

Balance of risks and benefits

Finally, and importantly, the studies looked into the balance of benefits and harms of taking aspirin in a healthy population. This is critical, because if people are considering taking aspirin for preventing cancer, we’ve got to be very sure about whether it does good or harm overall.

As the graph below shows, over time, the benefit – lowering cancer risk – increased, while the risk of serious side effects, like internal bleeding, got smaller. Crucially, in the first three years of taking aspirin, the risk of serious internal bleeding was much higher in aspirin-takers than those who weren’t on the drug:

A graph showing how risks change over time when taking aspirin

This risk went down over time, and after 5 years of taking the drug, the risk of internal bleeding was back at the same level as people who weren’t on the drug.

Overall, the risk of all the outcomes combined – cancer, serious internal bleeding and major heart and circulatory problems – was lower in the aspirin group. That seems to show the balance could be tipping to the benefit side. Here are the raw numbers:

Aspirin graphic

But that’s not the only consideration – if people stop taking aspirin daily, their risk of a stroke goes up.

And certain people definitely shouldn’t take aspirin, because they’re at higher risk of serious complications. That includes people with asthma, stomach ulcers, haemophilia, or anyone taking other drugs that might interact badly with aspirin.

So what should I do?

The first and most important thing is that if you’re considering starting to take aspirin daily, discuss it with your GP first, or your cancer specialist if you’ve been diagnosed with cancer.

In particular, there might be a reason why taking aspirin every day would be a bad idea for you personally – despite what the overall evidence says. And it’s worth discussing the benefits and harms, taking into account your own and your family’s medical history.

And if you do get the go ahead from your own doctor, you should make sure you don’t take aspirin on an empty stomach.

Today’s results are encouraging, and add to our understanding of the effects of taking aspirin daily. But there are still questions to answer. For example:

  • What is the optimal period of time to be taking aspirin for?
  • At what age does the biggest benefit and smallest risk occur?
  • Who is most likely to benefit, and who is most likely to get side effects?
  • And how can we minimise the risk of a stroke when people stop taking the drug?

Cancer Research UK scientists are running trials at the moment that aim to answer some of these questions.

And we’d also like to see some analysis and advice from the Governement about whether aspirin should be recommended more widely.

Until this is the case, taking aspirin should still be a decision you take in consultation with your doctor.



  • Rothwell, P et al, Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits in 51 randomised controlled trials, Lancet (2012) DOI:10.1016/S0140-6736(11)61720-0
  • Rothwell P et al, Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trial, Lancet (2012) DOI:10.1016/S0140-6736(12)60209-8
  • Algra A & Rothwell P, Effects of regular aspirin on long-term cancer incidence and metastasis: a systematic comparison of evidence from observational studies versus randomised trials, Lancet Oncology (2012) DOI:10.1016/S1470-2045(12)70112-2