Aspirin provides overall protection against cancers, especially those affecting the stomach and bowel, a large study has found.
Scientists in the US analysed 32 years-worth of data from almost 136,000 participants in two major health investigations involving nurses and doctors.
They found that those who took aspirin regularly had a 3% lower risk of developing any type of cancer than those who did not.
Most of the effect was due to the painkiller's impact on cancers of the gastrointestinal tract. Taking aspirin regularly reduced the risk of colorectal (bowel) cancer by 19% and of gastrointestinal cancer by 15%.
No specific reduction was seen in the risk of breast, prostate or lung cancers.
Aspirin's protective benefit appeared after five years of continuous use at dosages ranging from a half to 1.5 standard tablets a week, or one low-dose pill a day.
Researcher Dr Andrew Chan, from Massachusetts General Hospital, said: "We now can recommend that many individuals consider taking aspirin to reduce their risk of colorectal cancer - particularly those with other reasons for regular use, such as heart disease prevention - but we are not at a point where we can make a general recommendation for overall cancer prevention.
"At this point, it would be very reasonable for individuals to discuss with their physicians the advisability of taking aspirin to prevent gastrointestinal cancer, particularly if they have risk factors such as a family history."
The research is reported in the journal JAMA Oncology.