It is used in hormone replacement therapy, treating symptoms of menopause such as hot flashes. Also used to treat breast and prostate cancer.

Quinestrol is the 3-cyclopentyl ether of ethinyl estradiol (the active metabolite). After gastrointestinal absorption, it is stored in adipose tissue where it is slowly released and metabolized principally to the parent compound, ethinyl estradiol. Ethinyl estradiol is a synthetic derivative of the natural estrogen estradiol.

Estrogens diffuse into their target cells and interact with a protein receptor (the estrogen receptor). Estrogen interacts with a target cell receptor. When the estrogen receptor has bound its ligand it can enter the nucleus of the target cell, and regulate gene transcription which leads to formation of messenger RNA.

The mRNA interacts with ribosomes to produce specific proteins that express the effect of estradiol upon the target cell. Estrogens increase the hepatic synthesis of sex hormone binding globulin (SHBG), thyroid-binding globulin (TBG), and other serum proteins and suppress follicle-stimulating hormone (FSH) from the anterior pituitary. Target cells include the female reproductive tract, the mammary gland, the hypothalamus, and the pituitary. Estrogens increase the hepatic synthesis of sex hormone binding globulin (SHBG), thyroid-binding globulin (TBG), and other serum proteins and suppress follicle-stimulating hormone (FSH) from the anterior pituitary. The combination of an estrogen with a progestin suppresses the hypothalamic-pituitary system, decreasing the secretion of gonadotropin-releasing hormone (GnRH).

This medication is used in women to prevent pregnancy after birth control failure (e.g., broken condom) or unprotected sex. It is a progestin hormone that prevents pregnancy by preventing the release of an egg (ovulation) and changing the womb and cervical mucus to make it more difficult for an egg to meet sperm (fertilization) or attach to the wall of the womb (implantation).Using this medication will not stop an existing pregnancy or protect you against sexually transmitted diseases (e.g., HIV, gonorrhea, chlamydia).This medication should not be used as a regular form of birth control.

How To Use

Take this medication by mouth as soon as possible after unprotected sex. Your instructions for use depend on the brand you take. Therefore, check the label on your brand and ask your doctor or pharmacist if you have any questions.

Take as directed, usually 2 tablets at once; or take 1 tablet and then take the second tablet 12 hours after the first tablet. This medication may be taken with or without food. This medication works best when it is taken within 72 hours (3 days) after unprotected sex.

If you vomit within 2 hours of taking a dose of this medication, contact your doctor to discuss whether you need to repeat the dose.The amount and timing of your period may be irregular after taking this medication. Notify your doctor immediately if your period is more than 7 days late. You may need to take a pregnancy test.

Side effects

Nausea/vomiting, abdominal pain, tiredness, dizziness, changes in vaginal bleeding, breast tenderness, diarrhea, or headache may occur.

If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.