Abstract
Long acting injectable hormonal contraceptives are among the most effective fertility regulating agents developed; yet they are also among the most controversial because of animal data indicating a possible carcinogenic potential in several species. A critical analysis of these animal findings has revealed, in all instances, the existence of specific mechanisms not occurring in the human. For this reason, most national and international scientific bodies who have reviewed this issue have concluded that there are no toxicological reasons for not using long acting hormonal contraceptives. Long acting agents can be divided into 2 separate groups: those having a duration of action of one month, which are composed of a long acting oestrogen and a progestagen, and those lasting for several months which consist of only a progestagen. Among the injectable progestagen-only contraceptives tested, only 2 have so far reached the international market: depot medroxyprogesterone acetate (DMPA), which has been administered at 3- or 6-month intervals and norethisterone enanthate, which has been injected at intervals ranging between 2 and 3 months. The most important side effect observed with these 2 agents is a complete disruption of the menstrual bleeding pattern, leading - in some cases - to total amenorrhoea, which is more frequent with depot medroxyprogesterone acetate than with norethisterone enanthate. The latter, however, has a shorter duration of action with a higher pregnancy rate than the former. Other adverse reactions are rare and of no real importance. Metabolic effects with progestagen-only injectable preparations are, in general, mild and less marked than with combined oestrogen-progestagen formulations. Recent investigations have shown that the return of fertility following their use is delayed but in no way impaired. Monthly injectable oestrogen-progestagen combinations have been tested to a more limited extent and these agents are available only in a very few countries. Their main advantage over progestagen-only preparations is that they allow a reasonable menstrual bleeding pattern in the majority of cases. Their obvious disadvantage is that they contain a long acting oestrogen.
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