The first birth control pill designed to stop monthly periods has been approved for use in the US.
Lybrel is designed to be taken continuously
The Food and Drug Administration backed continuous use of the pill, Lybrel, which is manufactured by Wyeth.
Taken daily it can halt a woman's menstrual periods indefinitely, as well as prevent pregnancies.
Standard contraceptive pills are designed to be taken for three weeks, followed by a week break to allow for menstruation.
An FDA official warned Lybrel was not suitable for everyone.
About half the women who tested it in trials dropped out before the end, citing irregular and unscheduled bleeding.
The pill contains a low dose of two hormones already widely used in birth control pills, ethinyl estradiol and levonorgestrel.
The continuous delivery of the hormones prevents the stimulation of a menstrual cycle.
A study showed Lybrel was just as effective in preventing pregnancy as a traditional pill called Alesse, also made by Wyeth.
But it may be difficult for the women to recognise if they have become pregnant because Lybrel users will not have regular periods.
Dr Vanessa Cullins, of the Planned Parenthood Federation of America Inc, welcomed the FSA decision.
She said it might potentially help women whose monthly periods were blighted by headaches, tender breasts, cramps and nausea.
However, Jean Elson, a sociologist at the University of New Hampshire, said: "For women in that situation, I certainly can understand the benefits of taking these kinds of medications, but for most women menstruation is a normal life event - not a medical condition.
"Why medicate away a normal life event if we're not sure of the long-term effects?"
That view was echoed by health psychologist Paula Derry in a recent editorial in the British Medical Journal.
She said: "A drug (that) chronically over-rides the physiological changes associated with the menstrual cycle (is) creating a hormonal environment that is not found in nature."
Toni Belfield, of the Family Planning Association in the UK, said: "For women who don't want to have a period often this is a very good option.
"It is important that contraception provides women with a choice, not just between different methods, but between how those methods are used."
Doctors have long allowed women to skip their periods by starting a new pack of conventional pills on day 22 of their cycle rather than waiting a week to resume the hormones.