Final answer:
Levonorgestrel, marketed as Norgestrel, is used for emergency contraception and as a component in birth control methods. It works by preventing ovulation or making fertilization and implantation difficult. It is known as the 'morning after pill' and is intended for use when primary contraception fails.
Step-by-step explanation:
The therapeutic use of Norgestrel (levonorgestrel) is primarily for emergency contraception, and it is also a key component in some birth control methods. Levonorgestrel works by preventing the release of an egg from the ovary (ovulation) or causing changes in the cervical mucus and uterine lining that make it harder for sperm to reach the uterus and harder for a fertilized egg to attach to the uterus. Levonorgestrel is the active ingredient in Plan B One-Step or Next Step, commonly known as the "morning after pill." While it is not the primary method of ongoing birth control, it is used as a backup method if primary contraception fails. It should not replace regular birth control methods due to its mechanism of action and efficacy.