This problem is solved, just not in pill form.

There's an old solution that allows men to reduce their sperm count, down to an effective-zero: raise the temperature of the testicles to be body temperature.

In ancient times bread bakers were known to not father as many children, until they stopped working the ovens. The heat shock protein disrupts sperm production for longer periods of time. HSP forms at 104 degrees, iirc.

One of my previous comments about this: https://news.ycombinator.com/item?id=28023798