Its impact on our lives has been so great that 40 years on it is known simply as the Pill. But, although it created arguably the biggest sexual revolution around the world, it is now almost as famous for sparking health scares as it is for transforming contraception and relationships.

When it was launched on the NHS in 1961, medical journal The Lancet hailed its arrival as "second only in importance to the nuclear bomb".

It was an unfortunate description which was to appear increasingly appropriate as the years passed.

In 1969, the first major health scare broke when the UK's advisory committee on safety of medicines warned that women taking pills containing higher doses of oestrogen were at greater risk of suffering thrombosis. By that time, around one million women were already on the Pill. Many were understandably alarmed by the committee's statement and a spate of unwanted pregnancies took place around Britain as worried women stopped taking the controversial tablets or switched brands.

Fast forward to 2007 and the Pill has been linked to almost every kind of cancer.

The picture today is very confused. For every study claiming that taking the contraceptive will increase a woman's risk of developing cancer, there is one stating that using the Pill can protect women from the deadly disease.

A new Scottish study released today epitomises the current situation.

Researchers at Aberdeen University say there is strong evidence that, overall, the Pill protects women from contracting cancer, leaving them up to 12% less likely to fall prey to the disease.

But the key word is "overall" - because the study also revealed that those same women have a "significant increased risk" of developing any cancer if they take the Pill for more than eight years.

And while the obvious conclusion appears to be to simply stop taking the Pill after eight years, researchers point to a further finding that women who do continue to use the contraceptive will benefit from a reduced risk of suffering from ovarian cancer.

All of this makes it increasingly difficult for women to decide whether to take the Pill at all - and if they do, which one to take, and for how long.

Professor Philip Hannaford, who conducted the latest research, firmly believes that the benefits outweigh the risks and is at pains to stress that women should have no fear in taking it. He said: "I would say that the Pill is remarkably safe. Obviously there is a balance. There will be some women who have an increased risk of developing cancer, but equally there will be some who would have developed cancer but don't as a result of being on the Pill.

"There is no evidence that one brand is particularly safer, or any more dangerous, than another. Personally I would suggest using an older, low-dose Pill, simply because we have got more experience of them.

"But even with new Pills, the risk is tiny compared to the risk of getting on a bus.

"The message is, don't be worried that you are on the Pill, or about what brand of Pill you are on.

"It's not perfect, but it is good for a lot of women and they should feel confident using it."

Reassuring words perhaps, but unanswered questions remain: not least how many years women should stay on the Pill to maximise the benefits and minimise the risks.

Mr Hannaford says it is impossible to give a figure.

"There is no magic number. It's up to the individual," he said.

On the positive side, however, Mr Hannaford's study also showed that the increased risk of cancer associated with taking the Pill disappears rapidly once a woman comes off the contraceptive.

And, conversely, the protective effects of being on the Pill last for at least 15 years after stopping taking it.

The fact that the Pill has been found to protect women against some cancers is less surprising given that it was originally developed by a scientist who was working on a new treatment for cervical cancer.

Carl Djerassi was in a small laboratory in Mexico searching for a way to save patients the pain of having a high dose of progesterone injected into the cervix when he hit upon creating an oral alternative of the dose - and the Pill was created.

The early fears about thrombosis in 1969 were followed by later scares in 1977 and 1995 when UK experts raised concerns linking seven brands to an increased risk of thrombosis.

The first cancer scare came in the 1970s, prompting numerous studies finding similarly worrying side effects.

However, simultaneously, studies were emerging showing that the Pill afforded women protection against certain cancers, including bowel cancer.

As experts debated, women still worried.

One organisation which has followed the changing revelations about the Pill is FPA, formerly known as the Family Planning Association.

It welcomed the new study which, it said, showed that the positive impact to health of the Pill is generally much greater than the negative side effects. It also suggested that the risks associated with the Pill might be caused by lifestyle choices such as smoking rather than the Pill.

Toni Belfield, FPA director of information, said: "This study further confirms that, for the majority of women who take the contraceptive Pill, the benefits far outweigh the potential risks.

"Research shows that there may be a slight increased risk of developing cervical cancer from oral contraception, but more work needs to be done to investigate other factors such as sexual activity and smoking."

Meanwhile, with so little clear direction on using the Pill, Mr Hannaford does at least have one simple message which all women can follow to counteract any potential risks, regardless of which choice they make.

"Keep as healthy as you can, take part in cancer screening services and be breast aware."

It is the only method that is both easy and reliable'
Case study: Patricia Hess has taken the Pill for the past 30 years.

According to the latest study into the contraceptive's side effects, that puts her at a significantly greater risk of developing all cancers.

Like many women, she has worried over the years about the damage she might be inflicting on her body by choosing to use the Pill.

Although she did go off it once for about six months because she was so concerned, she started taking it again because she could not find a better alternative.

And while conflicting studies continue to be published linking the contraceptive to both causing and preventing cancer, she has decided it is better to ignore them and just get on with her life.

Now in her late 40s and separated with no children, the PR manager, who lives near Kinross, said: "I don't like taking drugs at all and I did get to the point where I wanted to try another method but the Pill was the only contraceptive which I found was reliable, easy and comfortable to use, so I went back on it.

"You have to balance the risks. It's the same with HRT. You've got to make your own assessment. If you based what you did on every latest piece of research you would always be wondering what the next survey was going to say. It's always changing. If you started worrying about everything that could potentially damage your life you would never leave the house.

"I have decided to stay on the Pill and do other things to balance the negative effects, like eating healthily and not smoking.

"If you can eliminate some factors these things all come down to probability, and you just have to get on with your life."