Levonorgestrel

Levonorgestrel (or l-norgestrel or -norgestrel) (Plan B, Next Choice, and others) is a second generation synthetic progestogen used as an active ingredient in some hormonal contraceptives, including combined oral contraceptive pills, progestogen only pills, emergency contraceptive pills, intrauterine systems, and contraceptive implants.

Read more about Levonorgestrel:  Chemistry, Side Effects