Using paracetamol regularly could reduce the risk of ovarian cancer by almost a third, a study says.
Researchers say pack sizes should be reduced further
A team from Athens University found the risk fell by 30% after analysing eight previous studies into the painkiller covering over 746,000 women.
But researchers warned long-term use could lead to an increase risk of liver and kidney failure, the British Journal of Clinical Pharmacology reported.
Experts said more research was needed into the effect.
And the report stressed the researchers were not suggesting that women start taking paracetamol to guard against the disease.
Ovarian cancer is not one of the most common cancers, affecting about one in 60 women.
But the mortality rate is high - less than a third survive for five years following diagnosis - as the disease is often hard to spot and therefore not identified until it is in its late stage.
The team reviewed studies covering paracetamol and ovarian cancer from 1966 to 2004 in the UK, US and Denmark. Some 4,405 of the women had ovarian cancer.
Regular use differed from study to study, but was most commonly referred to as at least 30 tablets a month.
Lead researcher Dr Stefanos Bonovas said due to the high mortality rate, focussing on prevention was the "most rational approach for reducing deaths".
"Strategies that focus on prevention may therefore provide the most rational approach for reducing deaths from this form of cancer.
"Because paracetamol is so widely used, a link with a decreased risk of ovarian cancer could have important public health implications."
But he added: "The risks of long-term paracetamol use - including liver and chronic kidney failure - may outweigh the potential benefits of preventing ovarian cancer in low-risk cases.
"But we do feel that our study highlights the need for further research into this highly important link between a simple over-the-counter medicine and a very aggressive form of cancer."
The study was unable to identify why the painkiller reduced the risk.
Dr Kat Arney, science information officer at Cancer Research UK, said the research was welcome, but also warned about the side effects.
She added: "The next step is to do laboratory research to understand more about how paracetamol achieves this protective effect and to test the benefits of the drug in a large-scale clinical trial."