Using the contraceptive pill cuts the overall risk of a woman developing cancer, research suggests.
Long-term use did raise the risk
Any increased risk of breast and cervix cancer linked to pill use appears to be cancelled out by long-term protection from other cancers.
However, the British Medical Journal study found using the pill for more than eight years was associated with an increased overall risk of cancer.
The University of Aberdeen analysed data from a 36-year study.
The study began in 1968, and updates on the women's health were provided every six months by their GPs.
Even if women eventually moved to a new GP the researchers were able to obtain details of whether they developed cancer, or died from NHS central registries.
The researchers found that the risk of cancer was up to 12% lower among those women who had taken the pill.
The reduced risk of large bowel, uterine and ovarian cancer was statistically significant.
The evidence suggests that the protective effect of taking the pill lasts for at least 15 years after stopping - often into the period when women become more susceptible to developing cancers.
However, women who used the pill for more than eight years - less than a quarter of pill users who took part in the study - had a statistically significant increased risk of developing cancer, particularly cervical and central nervous system cancer.
But the same women were at reduced risk of developing ovarian cancer.
The researchers said the findings should reassure many women, especially those who used first generation oral contraceptives.
They accept that different modern pill formulations, and a different pattern of usage - with women now taking the pill at a younger age, and staying on it for longer - may both modify the risk of cancer.
But they argue that evidence from other studies suggests that currently available pills produce broadly similar effects.
Lead researcher Professor Philip Hannaford said it was still "quite unusual" for women to take the pill for as long as eight years, as they tend to use the pill on and off depending on their personal circumstances.
He said: "I would not recommend women take the pill specifically to reduce their risk of cancer, but if they decide to take it then they are not going to be putting themself at risk by doing so."
Toni Belfield, of FPA (Family Planning Association), said: "This study adds to the evidence that as well as providing a safe and effective form of contraception, the contraceptive pill can help protect against the risk of different types of cancer.
"The study further confirms that for the majority of women who take the contraceptive pill the benefits far outweigh any potential risks."
Dr Julie Sharp, of the charity Cancer Research UK, said: "It remains important for women to be aware of the short-term risks of using the Pill, such as an increased risk breast and cervical cancer, but this research suggests that these risks may be balanced out by health benefits over the longer term."
In the UK, an estimated three million women use the Pill each year, and 100 million around the world.
More than 300 million women are thought to have used the Pill since its launch in 1961.