Contraceptive Drugs : Combined Pill and its Mode of Action, Benefits and Adverse Effects

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Birth control pill

Birth control pill (Photo credit: Wikipedia)

What are Oral Contraceptives?

Oral contraceptives

Oral contraceptives are the drugs which are used for preventing the unwanted pregnancy. They are taken orally for 21 days. They act by mimicing the pregnancy like environment with the help of hormones present in the contraceptive pills.

Types of Oral Contraceptive pills:

There are two main types of oral contraceptives:

  1. The combined pill (combination of an oestrogen and progestogen)
  2. The progestogen-only pill

The Combined Pill

  • The combined oral contraceptive pill is extremely effective, even in the absence of inter-current illness and of treatment with potentially interacting drugs.
  • The oestrogen in the most of the combined pills is ethinylestradiol, a few preparations may also contain mestranol.
  • The progestogen in the combined pill may be norethisterone, levonorgestrel, ethynodiol, desogestrel or gestodene which are more potent.
  • They have less androgenic action and causes a minor change in the lipoprotein metabolism. It may cause a major risk of thromboembolism.
  • The oestrogen content will be generally 20-50 micrograms of ethinylestradiol. The preparation have to be chosen such that it contains low amount of oestrogen and tolerable amount of progestogen so that it gives good cycle control in the individual women.
  • The combined pill is taken for 21 consecutive days followed by 7 pill-free days, which causes a withdrawal bleed. Normal cycles of menstruation usually commence fairly after discontinuing treatment. Permanent loss of fertility is rare and if it occurs it may be due to early menopause rather than long term consequence of the contraceptive pills.

Mode of action of the combined pill:

  • Oestrogen inhibits the secretion of the follicle stimulating hormone (FSH) and suppresses the development of the ovarian follicle by negative feed back mechanism on the anterior pituitary.
  • Progestogen inhibits the secretion of the luteinizing hormone (LH) and prevents the ovulation. It also makes the cervical mucous less suitable for the passage of the sperm.
  • Oestrogen and progestogen act in harmony to alter the endometrium so as to prevent implantation.
  • They also interfere with the coordinated contractions of the cervix, uterus and fallopian tubes that facilitate fertilisation and implantation.

Beneficial effects of the combined pill

  1. Combined pills are being used by women worldwide for contraception since 1960s effectively.
  2. It is a safe and effective method of contraception.
  3. The combined pill markedly decreases menstrual symptoms like irregular periods and intermenstrual bleeding.
  4. Iron deficiency anaemia is reduced.
  5. Premenstrual tension gets reduced.
  6. Benign breast disease, uterine fibroids and functional cysts get reduced or prevented.
  7. Unwanted pregnancy and maternal mortality can be avoided.

Common adverse effects of the combined pill

  1. Weight gain, which may be due to retention of the fluid or an anabolic effect.
  2. Mild nausea
  3. Flushing
  4. Dizziness
  5. Depression
  6. Irritability
  7. Skin changes like acne and increased pigmentation.
  8. Amenorrhoea of variable duration on cessation of taking the pill.
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