Research suggests 25% of British women take the contraceptive pill
Women are not given enough information about long-term reversible methods of contraception, research suggests.
Some 76 out of 100 women told the Family Planning Association they had never heard of internal hormone device - the intrauterine system (IUS).
A third knew nothing of intrauterine devices, or coils, and 24% did not know of the contraceptive implant. Some 12% had not heard of hormone injections.
The FPA said women had a right to know about every method of contraception.
Research in 2004-5 suggested that one-in-four women aged 16-49 used the contraceptive pill, while only 9% used one of the four long-acting reversible contraceptive (LARC) methods.
But the FPA's information manager Angela Reynolds says that once women know about all the options, they often choose one of these methods.
"Very many women feel they have only got one choice. We believe that every women should know about them and we believe these methods have not had a good enough airing."
Apart from being the most reliable forms of contraception with 99.9% success rates, some long-term methods have other health benefits.
For example the intrauterine system or IUS, which involves a progestogen-producing device being implanted into the womb, is helpful for women with very heavy periods.
IUD or coil - A small plastic and copper device which is fitted into the womb by a specially trained doctor or nurse
IUS - A small plastic T-shaped device which releases the hormone progestogen into the womb
Implant - A small progestogen implant about the size of a hair grip placed under the skin on the inside of the top of the arm
Injection - A hormone progestogen jab given every 8 or 12 weeks normally into the bottom
While many other women are unable to tolerate oestrogen, a hormone contained in the traditional contraceptive pill, for health reasons.
"So for these women - these methods offer highly effective alternatives.
"There are myths about many of these methods and we are trying desperately to dispel these myths," said Mrs Reynolds.
FPA policy manager Caroline Davey says research shows there are clear financial advantages to wider use of long-term methods.
"By increasing the proportion of methods that are long acting we can save a significant amount of money - £500 million over 15 years."
The savings would result from reducing pressure on maternity services and cutting the number of abortions, she says.
Last October, the National Institute for Health and Clinical Excellence said 70,000 of unplanned pregnancies could be prevented of more women used LARC methods.
A Department of Health spokeswoman said £40 million was being invested over the next two years to ensure women had information about all contraceptives.
She added that more primary care trusts were being made aware of LARC options.
But she also as said it was important women were warned of the dangers of having unprotected sex a national advertising campaign was being launched.
A spokeswomen for Brook, the sexual health charity for young people, said the important thing was that people got information about all the options - including LARC.
"But people need to think about protecting themselves from sexually transmitted diseases as well so they will need to use a condom as well."