Yaz tablets contain a combination of drospirenone and ethinyl estradiol. Drospirenone and ethinyl estradiol prevent ovulation (the release of an egg from an ovary) and also cause changes in your cervical and uterine lining, making it harder for sperm to reach the uterus and harder for a fertilized egg to attach to the uterus. (from Drugs.com)
Alternatives: Using a combination of herbs, awareness of the woman's cycle and injaculation (male semen retention) you can get pretty close to 100% contraceptive effectiveness. Californian apricot seeds, Queen Anne's Lace and Neem Oil are herbs that can be used episodically to inhibit implantation and prevent pregnancy.
Alternative Drugs: Levora, Trivora, Mercilon.
