Hormones Used in Contraceptives
Estrogen (Estradiol)
Estrogen is the major female hormone and is responsible for female characteristics. The estrogen compound used in most oral contraceptives is estradiol and is always used with a progestin.
Effects on Reproduction. When used throughout a menstrual cycle with progesterone, it suppresses the actions of other reproductive hormones (luteinizing hormone, or LH, and follicle stimulating hormone, or FSH) and prevents ovulation. Estrogen also changes the cellular structure of the lining of the uterus (the endometrium) and hinders implantation of a fertilized egg.
Side Effects of Estrogen. During the first 2 - 3 months of use of oral contraceptives, side effects from estrogen in the combined pill include:
- Nausea and vomiting (can often be controlled by taking the pill during a meal or at bedtime)
- Headaches (in women with a history of migraines, they may worsen)
- Dizziness
- Breast tenderness and enlargement
Progesterone (Progestin)
When used in contraception, progesterone is referred to by one of several names:
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Progesterone is the name for the natural hormone
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Progestogen is a synthetic form
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Progestin is the term for any hormone, natural or synthetic, that causes progesterone effects; it is used as the general term in this report
Progestins may be used alone or with estrogen in oral contraceptives. In addition, certain specific progestins are used in other kinds of contraceptives, such as etonogestrel in the Implanon implant and depo-medroxyprogesterone acetate in the injected Depo-Provera.
Progesterone can prevent pregnancy by itself in several ways:
- It blocks luteinizing hormone (LH), one of the reproductive hormones important in ovulation.
- It maintains a powerful barrier against the entry of sperm into the uterus by keeping the cervical mucus thick and sticky.
- It reduces the mobility of the fallopian tubes, thereby inhibiting sperm transport.
- It changes the lining of the uterus and makes it more difficult for the fertilized egg to implant.
Progestins used in contraceptives are referred to as:
- Second generation (levonorgestrel, norethisterone).
- Third generation (desogestrel, gestodene, norgestimate, drospirenone). The third-generation progestins tend to have fewer male-like side effects. Some studies suggest, however, they may pose a higher risk for blood clots than the older progestins, although the risk is still small.
Side Effects of Progestins. Side effects of progestin occur in both the combination oral contraceptives and any contraceptive that only uses progestin, although they may be less or more severe depending on the form and dosage of the contraceptive. Side effects may include:
- Changes in uterine bleeding such as higher amounts during periods, spotting and bleeding between periods (called break-through bleeding), or absence of periods
- Unexpected flow of breast milk (check with your doctor if this occurs to be sure other abnormalities are not causing it)
- Abdominal pain or cramps
- Diarrhea
- Fatigue, unusual tiredness, weakness
- Hot flashes
- Decreased sex drive
- Nausea
- Trouble sleeping
- Acne or skin rash (not all OCs have this side effect; low-dose OCs actually improve acne)
- Depression, irritability, or other mood changes (although some OCs are helpful for women with premenstrual dysphoric syndrome)
- Swelling in the face, ankles, or feet
- Weight gain (however, combination oral contraceptives -- which contain progestins -- do not cause weight gain)
Newer formulations of combination pills that use low-dose estrogen, and newer progestins may reduce and even avoid many of these side effects, including weight gain. Low-dose progestins used in non-oral contraceptives, such as the LNG-IUS IUD, also may not pose as high a risk for these side effects. If side effects persist or are severe, a woman should always talk to her doctor. Many women do not experience these side effects, or for many of those who do, their bodies eventually adjust.
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