Testosterone undecanoate taken for 10 days does not cause azoospermia; problems in sperm production and transportation may lead to azoospermia. Testosterone undecanoate is used in testosterone supplementation therapy for primary or secondary hypogonadism and can be used to treat infertility due to disorders of spermatogenesis; taking testosterone undecanoate for 10 days will not cause azoospermia. There are many causes of azoospermia, including testicular spermatogenic dysfunction or a deficiency of hormones that affect the spermatogenic process in the testes can lead to the testes failing to produce sperm, and also disorders of vasovaginal obstruction can lead to sperm failing to exit the body. If you suspect azoospermia, you need to go to the hospital for a clear and relevant examination to find out the specific cause of the disease, and then choose the appropriate treatment plan.