The evidence that over-the-counter (OTC) medications can benefit our long-term health in meaningful ways keeps accruing. Aspirin, ibuprofen, and acetaminophen all have various health benefits, but aspirin is emerging as a key player in the fight against cancer. Three new studies by the same research team have shown that aspirin over the long term can reduce the risk of cancer – and its spread through the body.

One type of cancer called metastatic adenocarcinoma, which can affect the prostate, lungs, and colon, was reduced by 46% in people who took aspirin.

The team’s earlier work had shown that daily aspirin could reduce cancer risk over the next 20 years. Now, Peter M. Rothwell and his team have expanded on their original findings. In one large scale review of 51 earlier studies, people who took less than 300 mg of aspirin every day had a 25% reduced risk of developing any type of cancer after three years. It reduced the risk of death from cancer by about 15%. The longer people took aspirin, the better: after five years, the risk of death was reduced by 37% in aspirin-takers.

Another study determined how aspirin affected the spread of cancer once it had developed. People who took at least 75 mg of aspirin a day had a 36% reduced risk of metastatic cancer than non-aspirin takers. One type of cancer called metastatic adenocarcinoma, which can affect the prostate, lungs, and colon, was reduced by 46% in people who took aspirin.

A third study was a confirmation of aspirin’s effects on metastasis. Looking at both observational studies and randomized trials (where participants are assigned to take the drug or not), metastatic cancers were reduced by 38% and 42% for observational and randomized trials, respectively. The reductions in risk were found for esophageal, colon, throat, biliary, and breast cancer.

The mechanisms by which aspirin may prevent cancer are still somewhat unclear. With regard to preventing metastasis, the fact that aspirin inhibits platelet cell functioning might contribute, since cancer metastasis is thought to hinge on platelet movement through the body.

Authors of an accompanying editorial point out that there are still some risks associated with aspirin itself, like gastrointestinal bleeding and stroke. One should always discuss with a doctor the decision to begin any medication, even OTCs.

That said, this series of studies may change the way we think about aspirin’s long-term impacts on health. Its role may not be solely in the prevention of heart disease, rather its effects may be much more widespread than previously imagined.

The studies were carried out at the University of Oxford. The first and second studies were published in The Lancet. The third was published in the journal Lancet Oncology.