Progestogen-only pill

The progestogen-only pill (POP), also known as the mini-pill, is a type of oral contraceptive that contains only progestogen hormones, unlike the combined oral contraceptive pill which contains both estrogen and progestogen. The primary function of the progestogen-only pill is to prevent pregnancy by altering the cervical mucus and the endometrial lining, and in some cases, suppressing ovulation.

Progesterone structure

Mechanism of Action

The progestogen-only pill works primarily by thickening the cervical mucus, which acts as a barrier to sperm penetration. This change in the cervical mucus is the main mechanism by which the POP prevents pregnancy. Additionally, the progestogen-only pill alters the endometrium (the lining of the uterus), making it less suitable for implantation of a fertilized egg. In some women, the progestogen-only pill also suppresses ovulation, although this is not its primary mechanism of action.

Types of Progestogen

There are several types of progestogens used in progestogen-only pills, including norethisterone, levonorgestrel, and desogestrel. Each of these progestogens has slightly different properties and may be chosen based on individual health needs and side effect profiles.

Norgestrel structure

Usage and Administration

The progestogen-only pill is taken orally, once a day, at the same time each day. Consistency in timing is crucial for maintaining its effectiveness. Unlike the combined pill, there is no "pill-free" week, and the POP must be taken continuously.

Effectiveness

When taken correctly, the progestogen-only pill is over 99% effective at preventing pregnancy. However, typical use, which may include missed pills or taking the pill at varying times, reduces its effectiveness to about 91%.

Side Effects

Common side effects of the progestogen-only pill include irregular menstrual bleeding, headaches, breast tenderness, and mood changes. Some women may experience no periods at all, while others may have more frequent or prolonged bleeding.

Advantages and Disadvantages

Advantages

• Suitable for women who cannot take estrogen.
• Can be used during breastfeeding.
• Lower risk of thrombosis compared to combined pills.

Disadvantages

• Requires strict adherence to daily timing.
• May cause irregular bleeding patterns.
• Does not protect against sexually transmitted infections (STIs).

Related Pages

• Combined oral contraceptive pill
• Contraception
• Hormonal contraception
• Family planning