Taking aspirin every other day cuts the risk of bowel and stomach cancers by more than 40 percent, states study.
They found that even a very low dose of the painkiller drastically reduces the odds of bowel and stomach cancers, the Daily Mail reported.
In the study, women who took one 100mg tablet every other day were 43 per cent less likely to get bowel cancer and 36 per cent less at risk of stomach cancer, after a period of 20 years.
So, taking a low dose of the drug every other day may protect patients from these side effects.
The researchers looked at the records of 39,876 women over 45. Half were told to take one 100mg aspirin tablet every other day for ten years while the remainder were given a placebo - a dummy drug.
At the end of the study the researchers compared how many women from each group had developed cancer and found no difference.
But when they looked at them again eight years later - 18 years after the study had started - they found the odds of developing bowel or stomach cancer amongst those on aspirin were significantly lower.
They think it may take several years for aspirin's beneficial effects to 'kick-in.'
Although experts are unsure exactly how it protects against cancer, they think it may stop certain harmful chemicals or enzymes in the body from working.
In particular they believe it blocks the Cox-2 enzyme - which exists on all our cells and is known to trigger cancer.
But lead researcher Professor Nancy Cook said patients should not start taking aspirin every day or every other day.
Addressing the National Cancer Research Institute conference in Liverpool, she said: "There are side effects. They are rarely fatal but they do cause the need for hospitalisation. The side effects do depend on the dose which is one reason we were testing taking 100mg every other day."
Although this research only involved women, Professor Cook said similar effects would be seen in men who took aspirin every other day.
The study only found that aspirin only protected against bowel and stomach cancer, it did not reduce the risk of breast and lung cancer.