Fertility vs Contraception: What's the Role of Testosterone?

Whenever I counsel a clinically hypogonadal patient about his options for optimizing his testosterone level, I always mention the possibility (probability, really) of inducing infertility with any testosterone product, whether injected, implanted or applied to the skin or gums.  Of course, the follow up question that's raised is whether or not the infertility is reversible.

Should any patient express even a hint or desire for future fertility, I always dissuade him against using a testosterone product as this will most likely induce pituitary suppression of FSH and thus sperm production.  Instead, I ask him to consider off-label use of some prescription medication to stimulate his testicles into producing more testosterone & sperm.  That way, he wins on both counts.

On the other hand, regardless of gonadal state, there is an interest in reversible male hormonal contraception, similar to that offered to women.  This is where testosterone has another role or purpose, that of specifically inducing infertility via azoospermia (no sperm).  But still, the question is asked, how long will it take to recover sperm production, and to what degree will this occur?  And will baseline sperm production affect the time to recovery?

In a study published online in the International Journal of Andrology earlier this summer, the authors concluded that injectable testosterone undecanoate (TU) is able to suppress sperm production below 1 million/ejaculate in 3 out of 4 men 20-45yo and even induce azoospermia in 1 out of 2 while failing to achieve either goal in approximately 1 out of 4 with baseline normal sperm counts.

In men with baseline low sperm counts, TU was able to suppress sperm production below 1 million/ejaculate in over two-thirds of this group, while inducing azoospermia in close to half; however, close to 1 out of 3 failed to achieve either goal.

So the good news is that sperm counts returned to baseline within 6 months of cessation of the intervention.  The bad news is that the TU regimen used was not able to achieve contraception in all patients.  From reading the study, it's not clear to me that the authors considered individualizing the regimen to achieve azoospermia rather than consider adding a progestin.

Ignoring the issue of intended contraception, one can then feel comfortable that younger men with hypogonadism can expect resolution of their induced infertility within 24 weeks of stopping testosterone therapy.  Given my druthers, I'd still suggest continuing with (way) off-label use of either clomiphene or human chorionic gonadotropin to stimulate both testosterone & sperm production in anyone who wants to maintain his fertility.  That way, the patient doesn't have to give up one goal to achieve the other.