It prevents pregnancy by emulating the hormonal balance of pregnancy. The original purpose of “the pill” was to correct a problem cycle. In my wife, it worked to do just that. By being on “the pill” for a year or so then dropping, she became pregnant with her first child. As with many medicines, the “side effect” became the market. (See “Viagra” for another example of this.)
Now here is another issue with “birth control”.
By altering the hormonal balance, it also alters the pheromone preference. In mammal studies, pheromonal preference for male company was genetically different…as in “not family” for non pregnant females. This makes sense as a mate choice would be made which resulted in genetic diversity in the offspring.
While pregnant, the male company preference switched to related males…siblings, uncles etc. From a wild standpoint this translates to “safety with the family”.
A woman on “the pill” will chemically, pheromonally prefer the company of genetically similar males…too close genetically to be prime mate material. Mate choices made while on “the pill” will result in genetically weaker offspring. Furthermore, once pregnancy is no longer a concern due to female menopause and “the pill” is no longer used the “chemistry” drops to that of siblings.
I have a personal testimony of this. My own wife, while on “the pill” and while pregnant with her first (not my biological child) only ever thought of me as a friend. We were friends for 5 years before anything remotely romantic came in. She was only physically attracted to me when she dropped “the pill”. It was like flipping a light switch.
So not only is “the pill” carcinogenic, it encourages poor genetic choices for reproduction.