This, the authors believe, may be the reason for the observed increase in susceptibility to SIV infection. The authors point out that the results of this animal study cannot be used to predict the effect of progestogens in human beings. To do that, carefully designed epidemiological studies will be needed.
All hormonal contraceptives contain a progestogen, either alone or in combination with an estrogen.
The observed thinning of the epithelium in the monkey study was due to progesterone alone. Thus, the concern raised in that study relates primarily to contraceptives that contain only a progestogen. At the present time information on the effect of currently used steroid hormone contraceptives on human vaginal epithelium is very limited. Some thinning of the epithelium has been observed under progestogen therapy. But there is no information at the present time to suggest that in women using progestogen-only contraceptives the epithelium is thinned to the same degree as seen in the monkeys in the study.