A “gonadotoxin” is the term for a substance, drug, or chemical that is toxic to sperm or eggs. In the modern industrial world, most gonadotoxins have come into existence over the past 100 years, which is why sperm counts have been declining over this time frame. These include tobacco, alcohol, marijuana, supplements, many pharmaceuticals, and chemicals and hormones that are put into our food. Of course, chemotherapy and radiation are one of the most potent gonadotoxins, so men who have been treated for cancer often suffer from infertility. These days, of the most common unrecognized sources of very low and zero sperm counts among men of reproductive age are testosterone, anabolic steroids, and even many over-the-counter workout supplements and testosterone boosters. External sources (called “exogenous” sources, which means something a man takes as a pill, injection, powder, or cream) of androgens, such as testosterone or anything even remotely related to testosterone, completely shut down sperm production. If a man of reproductive age is found to have low testosterone, he should meet with an endocrinologist or urologist to discuss alternative ways of raising testosterone before starting testosterone. This is not something I do as a fertility urologist, although I am able to make recommendations and prescribe the antidote medications to the testosterone poison if a man is looking to conceive a child in the near term and has already been taking testosterone. Therefore, if a man has been found to have a low or zero sperm count during an infertility evaluation, and he has been taking any type of testosterone in the recent or sometimes even in the remote past, he needs to make an appointment with us to sort this out!