As authors of the book reviewed by Randi Epstein (Testosterone: An Unauthorized Biography, Nature 574, 474–476; 2019), we wish to clarify two issues.

The first concerns Epstein’s assertion that testosterone and its precursor, DHEA, have a role in the maturation of ovarian cells. She suggests that “DHEA might boost fertility directly or as a mediator of oestrogen production”. But our reading of the evidence indicates that DHEA’s positive effect on fertility is not because it mediates oestrogen production but because it is converted to testosterone. In our book, we describe studies in animal models showing that blocking the conversion of DHEA to oestrogen doesn’t reduce DHEA’s effects, whereas knocking out androgen receptors creates major fertility problems in females, including premature ovarian failure.

The second issue concerns Epstein’s implication that our case for testosterone’s role in ovulation rests on interviews with a single clinician. In fact, our conclusions are based on more than a dozen studies in non-human animals, and on a comprehensive analysis of original research and review articles on the use of DHEA or other androgens to boost the response to fertility treatment in women. The interview with the clinician simply served as a ‘hook’ for the story.