Regular aspirin use has been linked to abdominal bleeds.
A study has suggested using aspirin could cut the risk of developing a type of stomach cancer by up to a third.
The British Journal of Cancer study looked at over 300,000 people.
It found those who had taken aspirin in the previous year were far less likely to develop cancer of the middle or lower stomach.
Taking aspirin regularly is known to cut the risk of bowel cancer, but can have side effects, including causing bleeds within the abdomen.
Such side effects mean that doctors advise against regular aspirin use as a protection against cancer.
This study followed 311,115 people for around seven years and analysed their use of the painkillers in the 12 months prior to the study starting.
A total of 73% of the group had used aspirin and 56% had used other NSAIDs at least once in the 12 months prior to the start of the study.
A quarter reported daily aspirin use while 10% reported daily use of other NSAIDs.
The rate of non-cardia stomach cancer calculated in this study was seven per 100,000 person-years for aspirin users, compared with 11 per 100,000 person-years for non-users.
Each year in the UK, around 8,000 people are diagnosed with stomach cancer, and around 5,250 people die from the disease.
There was also a 32% reduction for the same type of stomach cancer, non-cardia gastric cancer, in people who used other types of non-steroidal anti-inflammatory drugs - or NSAIDs - such as ibuprofen.
In contrast to results of previous studies, the researchers found that aspirin does not protect against oesophageal cancer and cardia gastric cancer - cancer of the top of the stomach.
Scientists believe that placebo controlled trials, which would assess risks and benefits should be conducted to see if NSAIDs can be used to protect against stomach and oesophageal cancers.
Five year survival rates for stomach cancers is just 15%, and for oesophageal cancers it is 8%.
'Talk to your doctor'
Dr Christian Abnet, of the National Cancer Institute in America who led the research, said: "We found that the risk of non-cardia stomach cancer was lower in people who had taken aspirin, and this risk lowered the more regularly they took it.
"Interestingly, our results didn't show a significant cut in the risk of oesophageal or cardia stomach cancer, so it's important that we continue to review data that suggests otherwise."
He added: "The number of people who survive at least five years following a diagnosis of stomach or oesophageal cancer is low, so it's important to increase our understanding of ways to prevent the disease and to investigate aspirin as a possible preventative drug."
He suggested that a further research should be carried out to further investigate the apparent protective benefits of aspirin and other NSAIDs, and the risk of side-effects.
Dr Lesley Walker, director of cancer information at Cancer Research UK, said: "It's far too early to recommend that people take aspirin to protect themselves from these cancers.
"In cancers where survival is low, understanding how to prevent the disease is crucial, but more research is needed to discover how side effects can be balanced with the benefits.
"Cancer Research UK would urge people to speak to their doctor before taking aspirin regularly."
Previous research has suggested regular long-term use of aspirin may be associated with an increased risk of pancreatic cancer.