Oral contraceptives (OCs) are classified according to the dosage of ethinyloestradiol (EE) and type of progestogen, and whether the dosages of EE and progestogen stay the same during the cycle, or change in a phasic manner. Ultimately, there is no statistically significant difference in efficacy between high-dose and low-dose OCs. There is also no difference in efficacy between monophasic and multiphasic products, which, other than having a lower hormone content, have no benefit over monophasic products.

Several medications, such as rifampicin, some of the anticonvulsants and certain human immunodeficiency virus (HIV) medications, may reduce the efficacy of OCs. Higher-dose OC preparations are recommended in patients taking these concomitant drugs.

The effectiveness of OCs with typical use is largely dependent on compliance, which is influenced by bleeding patterns and side-effects. In this regard, the composition of an OC may play a significant role. The dosage of EE and type of progestogen may relate to specific non-contraceptive benefits, such as improvement in dysfunctional uterine bleeding, dysmenorrhoea, premenstrual tension, endometriosis, iron deficiency anaemia, hyperandrogenism and acne. The third- generation progestogens and anti-androgens are generally regarded as more “skin friendly”.

The cardiovascular safety of OCs has long been controversial, and although complications such as myocardial infarction and stroke have been reduced over the years with lower EE dosages, the risk of venous thromboembolism (VTE) has not decreased consistently. In fact, some of the low-dose products containing third-generation progestogens and anti-androgens may be associated with a higher risk of VTE.

Breast cancer is another controversial issue that is associated with OC use. Epidemiological studies do not report an increased risk, whereas other meta-analyses do. The risk may be amplified by genetic susceptibility, although data on the subject are not consistent.

An increased risk of hepatic adenoma and cervical cancer has also been noted with OC use, but the latter seems to be dependent on persistent human papillomavirus infection. On the other hand, ovarian and endometrial cancers are reduced by the use of OCs, although genetic susceptibility may also modify the risk.

As indicated by several studies on risk factors relating to the safety of contraceptives, the choice of contraceptive is more complicated in patients with certain medical conditions. This is because the physiological changes and side-effects that are associated with the method may increase the risk of morbidity or mortality in these women. Before starting on a contraceptive, the woman should undergo a risk-benefit assessment to ensure the safety of the method. This is also true for OCs, and in this regard, the latest World Health Organization (WHO) safety categories may be consulted.