How Hormonal Birth Control Works
The 3 Ways
Prevents Ovulation
Thickens cervical mucus so the sperm cannot reach the egg to conceive
Makes the uterus inhospitable for a fertilized egg, so that it cannot implant itself in the uterus. Unfortunately, many women who understand that life starts at conception might not realize this could be happening to them. Many websites and doctors do not mention it.
https://www.reproductivefacts.org/news-and-publications/patient-fact-sheets-and-booklets/documents/fact-sheets-and-info-booklets/hormonal-contraception/
https://www.ucsfhealth.org/treatments/medical-abortion
Potential Side Effects
Depression (even more significant in teen girls)
Weight Gain
Mood swings
Decreased libido
May increase risk of breast cancer
Increased risk of stroke
Blood clots (rare but serious)
And other rare symptoms like your eye shape changing (Yes, this happened to me)
Effectiveness
The combination and the progestin only pill have a normal efficacy rate of 91%. That means 9 out of every 100 women will get pregnant on the pill.
https://www.healthline.com/health/healthy-sex/how-effective-is-birth-control#comparison-chart