The contraceptive pill is an effective and safe method of preventing pregnancy. The progestins used for contraception are components of a combined hormonal contraceptive or used alone in progestin-only formulations. Progestin-only contraceptives are available as daily oral preparations, subcutaneous or intramuscular injectables (every 1–3 months), subdermal implants (every 3–5 years), and intrauterine systems (every 3–5 years). Long-acting progestins are highly effective in typical use and have a shallow risk profile and few contraindications.
A new progestin-only, oestrogen-free contraceptive, drospirenone, in a dosage of 4 mg/day in a 24/4 regimen, has received regulatory approval in the USA and the EU. The molecule has antigonadotropic, antimineralocorticoid, antiestrogenic and antiandrogenic properties.
The regimen was chosen to improve the bleeding profile; maintain plasma oestradiol levels at those of the early follicular phase. It is necessary to avoid hypoestrogenism; and preserve efficacy even with a missed pill, as drospirenone has a half-life of 30–34 h.
Clinical studies have shown good efficacy, shallow cardiovascular side effects, a good bleeding pattern, and the maintenance of ovulation inhibition after scheduled 24 h delays in pill intake.