Structural Biochemistry/Plan B



The chemical IUPAC name is 13-ethyl-17-ethynyl-17-hydroxy- 1,2,6,7,8,9,10,11,12,13,14,15,16, 17- tetradecahydrocyclopenta[a] phenanthren-3-one. Its chemical formula is C_21H_28O_2. Levonorgestrel is the left form (D- form) of norgestrel. Herschel Smith first synthesized the drug in the 1960s under Wyeth Pharmaceuticals. This drug is primarily used as an emergency contraceptive

This drug is usually taken orally, in pill form and is more commonly known as Plan B or the morning after pill. Many users mistake the drug for an abortion pill. It should be made clear that Levonorgestrel will not terminate a matured fetus. The drug is only effective in preventing pregnancy by means of postponing ovulation and hindering sperm migration. Levonorgestrel is a common ingredient in other birth control pills and acts in the same way, but the levels of hormone in Plan B and other emergency contraceptives are much higher.

In the Body:Edit

As a progestin steroid, Levonorgestrel blocks ovulation by stopping the follicle-stimulating hormone and luteinizing hormone from being secreted from the pituitary gland. The drug also causes the mucus in the cervix to become more viscous which makes it difficult for sperm to travel far in the uterus, preventing implantation of the egg.


Oral contraception: At low doses, levonorgestrel is used in monophasic and triphasic formulations of combined oral contraceptive pills, with available monophasic doses ranging from 100-250 µg, and triphasic doses of 50 µg/75 µg/125 µg. At very low daily dose of 30 µg, levonorgestrel is used in some progestogen only pill formulations.

Emergency contraception: Levonorgestrel is used in emergency contraceptive pills (ECPs), both in a combined Yuzpe regimen which includes estrogen, and as a levonorgestrel-only method. The levonorgestrel-only method uses levonorgestrel 1.5 mg (as a single dose or as two .75 mg doses 12 hours apart) taken within 3 days of unprotected sex, with one study indicating that beginning as late as 120 hours (5 days) after intercourse could be effective. There are many brand names of levonorgestrel-only ECPs, including: Escapelle, Plan B, Levonelle, Glanique, NorLevo, Postinor-2, i-pill, "Next Choice" and 72-HOURS. The primary mechanism of action of levonorgestrel as a progestogen-only emergency contraceptive pill is to prevent fertilization by inhibition of ovulation. The International Federation of Gynecology and Obstetrics (FIGO) has issued a statement that: "review of the evidence suggests that LNG [levonorgestreol] ECPs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling."In June 2012, a New York Times editorial called on the FDA to remove from the label the unsupported suggestion that levonorgestrel emergency contraceptive pills inhibit implantation.

Intrauterine system: Levonorgestrel is the active ingredient in the Mirena intrauterine system.

Contraceptive implants: Levonorgestrel is the active ingredient in Norplant and Jadelle.

When and How to take Levonogestrel:Edit

Plan B should be taken no later than 72 hours after unprotected sex, but is most effective within 24 hours to prevent pregnancy. The sooner you take it, the better. Plan B can be purchased at most local drug stores and pharmacies without a prescription for women 18 years and older. Anyone under 17 will need a prescription from a doctor. Plan B should not be used in place of regular birth controls, but ONLY in emergency if:

  • no condom was used during sex, or the condom broke
  • no birth control was used/or a pill was skipped
  • regular birth control fails
  • the partner didn’t pull out in time
  • sex was forced.

Do NOT take Plan B if already pregnant.

Side Effects and Warnings:Edit

Side effects vary in severity and occurrence for each person. These include:

  • headaches
  • dizziness
  • fatigue
  • nausea/vomiting
  • abdominal pain
  • tender breasts
  • irregular menstruation

More serious side effects such as itching and skin rash should immediately be taken to the doctor. Those with diabetes and those who are breast-feeding should take extra precaution when using Plan B.

Always be aware of any possible drug interactions when taking a new medication. Consult a doctor before taking Plan B and inform them of any current medications.