Medieval alchemists, and more recently Harry Potter, spent time seeking the Philosopher's Stone. It was thought to be the elixir of life, bestowing long life and perhaps even immortality. Fifty years ago this month, a genuine philosopher's stone was discovered — only it was a small, white, circular tablet called Enovid, the first oral contraceptive.

I knew the biologists who developed "the pill" and the doctors who tested it. In the 1960s, as a young obstetrician in Britain, I began prescribing oral contraceptives. I saw how they gave women a freedom they'd never known. For the first time in history, women could choose if and when to have a child with relative ease. No uncertain rhythm method, no embarrassing interruption of lovemaking to put on a condom. Just a highly effective, easy-to-use method.

Yet from the get-go the pill was intensely controversial. Would women become sexual hedonists? Would the pope approve its use? Was the pill so dangerous it should be taken off the market? The early oral contraceptives had much higher doses of hormones than are used today, and there were deaths from blood clotting. The dangers hit the headlines.

Ultimately, the real test of whether any drug is safe to use for long intervals is to follow users for long intervals. I remember the decision made in Britain in 1968 to study 23,000 women using the pill and to compare them with 23,000 women not using the pill.

In March, the British Medical Journal published a stunning 39-year follow-up of these same women, with a mind-boggling cumulative total of 1.2 million women-years of observation. At last we have the information we needed for so many decades. We can say with unprecedented confidence that the pill is indeed a philosopher's stone, extending life by a measurable amount.

The pill is the only drug a doctor can prescribe that is known to prevent cancer. The reasons go back a long way in human prehistory. In the 1920s, explorers in the highlands of New Guinea found 1 million people literally living in the Stone Age — the people we must look to for understanding the patterns of success in evolution. Studies show that these women did not have their first menstruation until they were 18 to 20 years old. They spaced their children several years apart by long intervals of breastfeeding.

Most women had 50 or fewer episodes of ovulation and menstrual periods in their lifetime. In the modern world, the age of puberty has plummeted and few women breastfeed for a long time. Today's woman may ovulate 300 times, which we now know can increase the risk of certain cancers. In short, modern living places some unnatural stresses on evolved patterns of female reproduction.

The pill suppresses ovulation, and in doing so, it halves the risk of developing uterine or ovarian cancer. Women who have used the pill are less likely to develop colon cancer and have fewer melanomas. The protective effects of having taken birth-control pills persist for many years after swallowing the last tablet. Over the long term, even heart disease deaths are fewer.

This does not mean that the pill is safe for everyone, and certainly women who smoke and are over age 35 should not use the method.

The pill and other methods of contraception also have important non-contraceptive benefits. Babies born too close together have an increased infant mortality rate. If all pregnancies in the world were spaced three years apart by using modern contraceptives, there would be 2 million fewer infant deaths each year. About half of the spectacular decline in maternal deaths in the West over the last century is because women are having fewer children.

So why does the pill continue to have a bad image? Contraception on the whole challenges strong patriarchal traditions. It took Japan 40 years to register the pill but only six months to approve Viagra. John Rock, the obstetrician who conducted the first trials of the pill in Boston, was a devout Catholic who went to Mass every day. He argued that the pill was natural because it imitated pregnancy and breastfeeding, and most people expected the Vatican to bless the new method as licit for Catholics.

Instead, in 1968, Pope Paul VI issued the encyclical Humanae Vitae condemning the pill. Rock and millions of Catholics stopped going to Mass, but popes up to and including Pope Benedict XVI have continued to tell Catholic women not to use birth-control pills.

Finally, the pill is misunderstood because it has remained a prescription drug. There is no reason why women need pelvic examinations before being prescribed an oral contraception. Scientifically, there is no reason not to sell it over the counter. It is safer than aspirin. Off-patent oral contraceptive pills, which are the ones we know the most about and which I would give my loved ones, cost less than 20 cents a pack to manufacture. The pill remains on prescription for reasons of pharmaceutical companies' profit rather than for the welfare of women. Not until the pill is on sale next to Extra Strength Tylenol will women believe how safe it really is.

There are, of course, in the era of HIV, many reasons to use condoms. But the pill can save the lives of infants and prevent maternal deaths. It reduces the burden of abortion. It is prerequisite for the autonomy of women, and it enables couples to express their love in physical ways without the fear of unintended pregnancy. The pill is truly a philosopher's stone. In a very real way, the pill is less unnatural in the modern world than doing nothing.

Malcolm Potts, a British obstetrician, is a UC Berkeley professor and has published extensively on contraception. He wrote this for the Los Angeles Times,