<Tr> <Th> Periods </Th> <Td> Frequently lighter, for some methods periods may stop altogether </Td> </Tr> <Tr> <Th> Weight </Th> <Td> No proven effect </Td> </Tr> <P> Hormonal contraception refers to birth control methods that act on the endocrine system . Almost all methods are composed of steroid hormones, although in India one selective estrogen receptor modulator is marketed as a contraceptive . The original hormonal method--the combined oral contraceptive pill--was first marketed as a contraceptive in 1960 . In the ensuing decades many other delivery methods have been developed, although the oral and injectable methods are by far the most popular . Altogether, 18% of the world's contraceptive users rely on hormonal methods . Hormonal contraception is highly effective: when taken on the prescribed schedule, users of steroid hormone methods experience pregnancy rates of less than 1% per year . Perfect - use pregnancy rates for most hormonal contraceptives are usually around the 0.3% rate or less . Currently available methods can only be used by women; the development of a male hormonal contraceptive is an active research area . </P> <P> There are two main types of hormonal contraceptive formulations: combined methods which contain both an estrogen and a progestin, and progestogen - only methods which contain only progesterone or one of its synthetic analogues (progestins). Combined methods work by suppressing ovulation and thickening cervical mucus; while progestogen - only methods reduce the frequency of ovulation, most of them rely more heavily on changes in cervical mucus . The incidence of certain side effects is different for the different formulations: for example, breakthrough bleeding is much more common with progestogen - only methods . Certain serious complications occasionally caused by estrogen - containing contraceptives are not believed to be caused by progestogen - only formulations: deep vein thrombosis is one example of this . </P>

Where do the hormones in the pill come from