How can the menstrual cycle be stopped?

Children's pubescence is a result of a decrease in the hormone "Melatonin" secreted by the pineal gland in the brain. Melatonin is a hormone produced during sleep, and is responsible for many phenomena related to our biological clock. The hormonal control of our body works by feedback. In the case of pubescence, it is a negative feedback. That is, pubescence is the result of the decrease in the levels of Melatonin. An example for the way this feedback works is being exposed to artificial lighting at nighttime. This is a modern phenomenon, about a hundred years old, causing a significant shortening in sleeping hours at night (hence, decrease in the level of Melatonin). If we add a rich and healthy diet the result is an early sexual maturity of children. This process interferes with the quality of life of many girls who mature sexually and get their monthly period before the age of ten.
Melatonin stimulates an area in the brain called the Hypothalamus. Decrease in Melatonin levels causes the Hypothalamus to secret GnRH (a chemical that releases sexual hormones) stimulating the production of the sex hormone FSH in the Pituitary Gland in the brain. This process is considered to be the opening shot for a new hormonal feedback, enabling fertilization every month. This feedback is called "the monthly period", but it is an artificial and unneeded feedback, that never existed in our distant past.
The natural feedback expected for the sexually matured female primate includes a short heat, during which fertilization occurs (and of course, pregnancy and childbirth). The next expected stage for the young primate female is a long period of devoted motherhood including breastfeeding.
In order to produce a contraceptive that is healthy and safe to use we must follow the stages in the   sequence of events for women. The big disadvantage of the existing contraceptives is the fact they ignore women's physical needs. Their bodies contain an ancient anticipation for continuous and obvious continuum derived from observing hunters-collectors:

1. Childhood
2. Pubescence
3. (First) Ovulation
4. Fertilization
5. Pregnancy
6. Childbirth
7. Devoted for baby care and breastfeeding it for a number of years
8. Weaning
9. Ovulation and starting the sequence again

The desired hormonal solutions are derived from two natural stages women are expected to go through in their lives. The first stage is childhood, and the second is motherhood. Planning the (natural) birth-rate of the mothers in mammals is based on the activity of two hormones: Melatonin and Prolactin. Hence, they can both be used today as effective and healthy contraceptives.

The hormone Melatonin
In a study that took place in England, towards the end of the 1990s, young women received Melatonin before they went to sleep. Women who participated in this study stopped ovulating during the time they were taking Melatonin. The researchers simulated the natural process occurring in our childhood, when Melatonin blocks the release of GnRH in the Hypothalamus. ¹ The experiment proved that it is possible to disconnect the start of the hormonal feedback causing menstruation, by an intelligent use of the hormone. It might be that in the near future, women will be able to use Melatonin regularly, until they decide to become mothers. Such use of Melatonin will put an end to wasting the motherhood resources, limited in quantity.

The hormone Prolactin
Prolactin is called "the motherhood hormone".  The hormone is secreted in the mother's brain in response to a baby suckling, and stimulates milk production in the mother's breast tissue. The release of the hormone guarantees an abundant supply of mother milk for as long as the mother wants to continue and breastfeed her baby. Prolactin was in our remote past a natural contraceptive for women. The reason for this phenomenon was that a high level of Prolactin in the blood of the mother prevents a new menstrual cycle during the time the mother continues nursing her baby. ² Prolactin is a potential effective and healthy substitute for the contraceptives available in the market. After all, the original population- control of our species is based on a high (and constant) level of Prolactin in mothers' bodies. That is: a smart use in the derivatives of the hormone may regain women's original (long lost) maternal control over population growth.

We can assume that already in the near future, any mother who chooses to nurse her baby will be able to be assisted with a supplement of synthetic Prolactin for tightening the bond with the baby. In third world countries for example, such a solution will be effective and healthy for mothers and babies, as well as a valuable economic saving.